19-1694; Rev 2; 12/07 KIT ATION EVALU E L B A IL AVA 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection Features The MAX4271/MAX4272/MAX4273 comprise a complete family of integrated 3V to 12V hot-swap controllers. They allow the safe insertion and removal of circuit cards into live backplanes. The discharged filter capacitors of the circuit card provide a low impedance to the live backplane. High inrush currents from the backplane to the circuit card can burn up connectors and components, or momentarily collapse the backplane power supply leading to a system reset. This family of hot-swap controllers prevents such problems by regulating the current to a preset limit when the board is plugged in, allowing the system to stabilize safely. After the startup cycle is completed, two on-chip comparators provide DualSpeed/BiLevelTM protection against short circuits, load glitches, and overcurrent conditions. In the event of a fault condition, the load is disconnected. Fault recovery is handled by unlatching (MAX4271), autoretry (MAX4272), or programmed (MAX4273) methods. The MAX4271 family includes many integrated features that reduce component count and design time. An onboard charge pump provides the gate drive for a lowcost, external n-FET. Integrated features like startup current regulation and current glitch protection eliminate external timing resistors and capacitors. Also featured are an open-drain status output to indicate a fault condition, and an adjustable overcurrent response time. The MAX4271 (latched fault protection) and MAX4272 (autoretry fault protection) come in 8-pin SO packages. The MAX4273 (full function) comes in the space-saving 16-pin QSOP package and 16-pin SO package. All parts are specified across the extended temperature range, and have an absolute maximum rating of 15V to provide extra protection against inductive kickback during board removal. Provide Safe Hot Swap for +3V to +12V Power Supplies with Few External Components Unique Current Regulation Architecture Minimizes n-FET Linear Mode Duration Autoretry Feature (MAX4272/MAX4273) DualSpeed/BiLevel Current Limit Protects Against Current Glitches and Short Circuits Power-On RESET (MAX4273) 15V Absolute Maximum Rating Protects Against Inductive Kickbacks During Board Removal Internal Charge Pump Generates Gate Drive for External n-MOSFET Status Output Pin Indicates Fault/Safe Condition Space-Saving 8-Pin SO, 16-Pin QSOP Packages DualSpeed/BiLevel is a trademark of Maxim Integrated Products. Pin Configurations appear at end of data sheet. ________________________Applications Base Stations RAID Remote-Access Servers Network Routers and Switches ISDN Ordering Information PART TEMP RANGE PINPACKAGE PKG CODE MAX4271ESA -40C to +85C 8 SO S8-1 MAX4272ESA -40C to +85C 8 SO S8-1 MAX4273EEE -40C to +85C 16 QSOP E16-1 MAX4273ESE -40C to +85C 16 SO E16-1 Typical Operating Circuit BACKPLANE VCC REMOVABLE CARD M1 N RSENSE 2.7V TO 13.2V VOUT CBOARD IN STAT GND ON SENSE GATE STAT CSPD ON MAX4271 MAX4272 CTIM GND CTIM ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 1 MAX4271/MAX4272/MAX4273 General Description MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection ABSOLUTE MAXIMUM RATINGS Current into INC, ON (Note 2) ............................................2mA Current into Any Other Pin ...............................................50mA Continuous Power Dissipation (TA = +70C) 8-Pin SO (derate 5.9mW/C above +70C)..................471mW 16-Pin QSOP (derate 8.3mW/C above +70C)...........667mW 16-Pin SO (derate 8.7mW/C above +70C)................696mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C IN to GND ............................................................................+15V STAT, OUTC, LLMON, AUXVCC to GND ...............-0.3V to +14V GATE to GND ..............................................-0.3V to (VIN + 8.5V) GATE to LLMON (Note 1).........................................-1V to +8.5V INC, ON to GND (Note 2) .........................................-1V to +14V CEXT to GND ...............................................-8.5V to (VIN + 0.3V) CSPD, CTON, REF to GND ...........-0.3V to the lower of (VIN + 0.3V) or +12V VSENSE, RTH, CTIM to GND.......................-0.3V to (VIN + 0.3V) Note 1: GATE can be pulled below LLMON, but current must be limited to 2mA. Note 2: INC and ON can be pulled below ground. Limiting the current to 2mA ensures that these pins are never lower than about -0.8V. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = +2.7V to +13.2V, TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = +5V and TA = +25C.) (Note 3) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS POWER SUPPLIES Input Voltage Range VIN Supply Current IQ 2.7 VON = VIN 0.6 13.2 V 1 mA CURRENT CONTROL Slow Comparator Threshold VSC,TH Slow Comparator Response Time tCSPD Fast Comparator Threshold VFC,TH TA = +25C VIN - VSENSE TA = TMIN to TMAX SENSE Input Bias Current IB,SENSE 55 56 mV 10 20 40 s CSPD = 100nF to GND 10 20 40 ms 45 50 55 MAX4273 only 5k on RTH to VIN TA = +25C TA = TMIN to TMAX 43.5 75k on RTH to VIN TA = +25C 675 TA = TMIN to TMAX 650 RTH = GND tFCD 50 CSPD = floating MAX4271/MAX4272 Fast Comparator Response Time 45 43.5 180 56 750 825 mV 840 200 220 10mV overdrive, from overload condition to gate discharging 350 VSENSE = VIN 0.2 10 ns A MOSFET DRIVER Startup Period (Notes 4, 5) tSTART Gate Charge Current IGATE 2 MAX4271/MAX4272 CTIM = 100nF 21 31 41 MAX4273 CTON = 100nF 21 31 41 ms No capacitor 5.5 s GATE = IN (Note 6) 100 A _______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection (VIN = +2.7V to +13.2V, TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = +5V and TA = +25C.) (Note 3) PARAMETER SYMBOL CONDITIONS MIN TYP Slow Turn-Off Time tSLOW,OFF Time from trigger to VGATE < 0.1V (triggered by either the ON input or the slow comparator), CGATE = 1000pF to GND Fast Turn-Off Time tFAST,OFF Time from current overload to VGATE < 0.1V (triggered by the fast comparator, during normal operation), CGATE = 1000pF to GND 15 Maximum Gate Protection Voltage Voltage at which internal zener clamp circuitry is triggered, measured with respect to VIN (MAX4271/MAX4272), measured with respect to VLLMON (MAX4273) 6.7 Minimum Gate Drive Voltage Measured with respect to VIN, IGATE = 8.5A VIN 5V MAX 60 s s 7.5 V VIN 2.7V 2.7 0.4 1 2.75 During startup (current regulation provided by fast comparator) 25 70 195 During normal discharge, due to a slow comparator fault in normal mode, or by ON going low 75 200 550 LLMON Overvoltage Threshold Startup is initiated only after VLLMON is less than this voltage (MAX4273) 0.1 GATE Overvoltage Threshold Startup is initiated only after VGATE is less than this voltage 0.1 LLMON Impedance Impedance to GND, after a fault (MAX4273) IGATE,DIS V 5 During fast discharge, due to a fast comparator fault in normal operation Gate Discharge Current UNITS mA A V 0.6 1 V k REFERENCE (MAX4273) Output Voltage VREF VREF, Load Regulation LOAD ON AND RESET COMPARATORS Threshold Voltage 1.164 IREF = 0 to 100A, VIN = 5V VIN = 5V, rising threshold at ON or INC Hysteresis VHYST Power-Supply Rejection Ratio PSRR Propagation Delay No load, VIN = 5V VREF, LINE 2.7V VIN 13.2V, no load Line Regulation tD,COMP 0.575 1.2 1.236 V 1 8 mV 0.6 3 mV 0.6 0.625 V 1 mV/V 3 2.7V VIN 13.2V 10mV overdrive, ON going positive or negative, INC going negative INC going positive mV s 10 100 150 200 ms _______________________________________________________________________________________ 3 MAX4271/MAX4272/MAX4273 ELECTRICAL CHARACTERISTICS (continued) MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection ELECTRICAL CHARACTERISTICS (continued) (VIN = +2.7V to +13.2V, TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = +5V and TA = +25C.) (Note 3) PARAMETER SYMBOL CONDITIONS Input can be driven to the absolute maximum limit without false output inversion Input Voltage Range Input Bias Current IB,COMP ON Pulse Width Low (Note 7) tRESTART MIN TYP -0.1 0.001 To unlatch a fault MAX4271, MAX4273 with CTIM = IN MAX UNITS 13.2 V 1 A s 20 DIGITAL OUTPUTS (STAT, OUTC) VSTAT 13.2, VOUTC 13.2 Output Leakage Current Output Voltage Low VOL ISINK = 1mA 1 A 0.4 V 2 s RETRY TIMING (MAX4272, MAX4273) Retry Timeout Period Default Retry Timeout Period tRETRY tRETRY (default) 100nF capacitor on CTIM (Note 5) 0.5 CTIM = no connection 1 176 s UNDERVOLTAGE LOCKOUT (UVLO) Threshold VUVLO Hysteresis VUVLO,HYST Delay tD,UVLO Startup is initiated when this threshold is exceeded at IN 2.25 2.67 100 Time the input voltage must exceed undervoltage lockout before startup is initiated 100 150 V mV 200 ms Note 3: All devices are 100% tested at TA = +25C. All temperature limits are guaranteed by design. Note 4: Startup period is the time during which the slow comparator is ignored and the fast comparator regulates the sense current. It is measured from the time ON is brought high. Note 5: Inferred from test with CTON = 10nF (MAX4273) and CTIM = 1nF. Note 6: The current available at GATE is a function of VGATE (see Typical Operating Characteristics). Note 7: Guaranteed by design. 4 _______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection 0.4 ON = GND 0.3 0.4 0.2 0.1 0.1 2 4 6 8 10 12 21 -15 10 35 60 180 85 0 2 6 8 10 12 14 TEMPERATURE (C) VIN (V) SLOW COMPARATOR THRESHOLD vs. INPUT VOLTAGE FAST COMPARATOR RESPONSE TIME vs. OVERDRIVE VOLTAGE FAST COMPARATOR RESPONSE TIME vs. TEMPERATURE 50.4 50.2 50.0 49.8 TA = +85C 49.6 400 RESPONSE TIME (ns) TA = -40C 49.4 500 450 VIN = 12V 350 VIN = 5V 300 VIN = 12V 400 350 VIN = 5V 300 VIN = 3V 250 250 VIN = 3V 49.2 49.0 2 4 6 8 10 12 200 200 14 1 10 100 1000 -40 -15 10 35 60 VIN (V) OVERDRIVE VOLTAGE (mV) TEMPERATURE (C) FAST COMPARATOR THRESHOLD vs. INPUT VOLTAGE TIME TO FAST DISCHARGE GATE vs. CGATE STARTUP PERIOD vs. INPUT VOLTAGE TA = -40C 204 202 TA = +25C 200 198 TA = +85C 196 194 10k 1k VIN = 12V 100 VIN = 5V 10 35 33 31 310 CTIM = 1nF TIME IN s 290 29 27 270 VIN = 3V 1 CTIM = 100nF TIME IN ms 330 tSTART (s) 206 NO EXTERNAL MOSFET DISCHARGE TO VGATE = 0.1V 85 MAX4271/3-09 350 MAX4271/3-08 208 100k TIME TO DISCHARGE GATE (s) MAX4271/3-07 210 18 MAX4271/3-06 TA = +25C 50.6 450 MAX4271/3-04 50.8 VFC,TH (mV) 4 19 VIN (V) 51.0 0 20 CSPD = 0 TIME IN s 190 0 -40 14 22 210 200 RESPONSE TIME (ns) 0 VIN = 3V 0.3 0.2 0 VSC,TH (mV) 0.5 23 CSPD = 110nF TIME IN ms 220 0.6 24 tCSPD (ms) 0.5 0.7 230 tCSPD (s) 0.6 VIN = 12V VIN = 5V 0.8 MAX4271/3-05 SUPPLY CURRENT (mA) 0.7 0.9 SUPPLY CURRENT (mA) ON = VIN IGATE = 10A ON = VIN MAX4271/3-03 240 MAX4271/3-02 0.9 0.8 1.0 MAX4271/3-01 1.0 SLOW COMPARATOR RESPONSE TIME vs. INPUT VOLTAGE SUPPLY CURRENT vs. TEMPERATURE 192 190 0 2 4 6 8 VIN (V) 10 12 14 0.1 0.01 0.1 1 10 CGATE (nF) 100 1000 25 250 0 2 4 6 8 10 12 14 VIN (V) _______________________________________________________________________________________ 5 tSTART (ms) SUPPLY CURRENT vs. INPUT VOLTAGE MAX4271/MAX4272/MAX4273 Typical Operating Characteristics (VIN = 5V, RSENSE = 100m, CBOARD = 47F, TA = +25C, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = 5V, RSENSE = 100m, CBOARD = 47F, TA = +25C, unless otherwise noted.) GATE CHARGE CURRENT vs. GATE VOLTAGE VIN = 3V 1.2 VIN = 12V 100 VGATE = 0 IGATE (A) 1.0 0.8 0.6 VIN = 12V 125 80 VIN = 5V 100 VIN = 5.0V VIN = 3.0V 60 VIN = 5V 75 40 50 20 25 VIN = 3V 0.4 0.2 0 0 2 4 6 8 10 12 14 16 18 20 2 4 6 8 10 12 14 16 18 20 -40 10 35 60 VGATE (V) TEMPERATURE (C) GATE VOLTAGE vs. INPUT VOLTAGE SLOW GATE DISCHARGE CURRENT vs. GATE VOLTAGE TIME TO CHARGE GATE vs. CGATE 300 IGATE (A) TA = +25C 15 TA = -40C 10 VIN = 3V 250 200 VIN = 5V 150 VIN = 12V 100 5 NO EXTERNAL MOSFET 0 0 2 4 6 8 10 12 0 14 2 4 6 8 100 VIN = 12V TO VGATE = 17V 10 1 VIN = 5V TO VGATE = 10V 0.1 VIN = 3V TO VGATE = 6V 0.01 TRIGGERED BY A FAULT OR BY ON FALLING 50 MAX4271/3-14 TA = +85C 350 0.001 0.01 10 12 14 16 18 20 0.1 1 10 100 VGATE (V) CGATE (nF) FAST GATE DISCHARGE CURRENT vs. VIN SLOW GATE DISCHARGE CURRENT vs. TEMPERATURE TIME TO SLOW DISCHARGE GATE vs. CGATE 350 VIN = 3V 300 IGATE (A) 3.0 2.5 250 200 150 2.0 VIN = 5V, 12V 100 1.5 FALLING VIN 0 1.0 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 VIN (V) VGATE = VIN TRIGGERED BY A FAULT OR BY ON FALLING 50 -40 -15 10 1000 TIME TO DISCHARGE GATE (ms) MAX4271/3-16 3.5 MAX4271/3-15 RISING VIN 400 100 NO EXTERNAL MOSFET DISCHARGE TO VGATE = 0.1V VIN = 12V 10 1 VIN = 5V 0.1 0.01 35 TEMPERATURE (C) 60 85 1000 MAX4271/3-17 VIN (V) 4.0 85 1000 TIME TO CHARGE GATE (ms) 20 400 MAX4271/3-13a IGATE = 10A 0 -15 VIN (V) 25 VGATE (V) 0 0 MAX4271/3-13 0 6 150 IGATE (A) 1.4 120 MAX4271/3-12 VIN = 12V MAX4271/3-10 FAST GATE DISCHARGE CURRENT (mA) 1.8 1.6 GATE CHARGE CURRENT vs. TEMPERATURE MAX4271/3-11 FAST GATE DISCHARGE CURRENT vs. VGATE FAST GATE DISCHARGE CURRENT (mA) MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection 0.001 0.01 VIN = 3V 0.1 1 10 CGATE (nF) _______________________________________________________________________________________ 100 1000 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection MAX4271/3-20 MAX4271/3-19 MAX4271/3-18 2.4 FAST GATE DISCHARGE CURRENT (mA) MAX4271/MAX4272 TURN-OFF TIME (EXTERNAL CGATE = 22nF, CBOARD = 470F) MAX4271/MAX4272 TURN-OFF TIME (CBOARD = 470F) FAST GATE DISCHARGE CURRENT vs. TEMPERATURE VIN = 3V VGATE = VIN 2.2 ON ON VGATE 2V/div ILOAD (1A/div) 2.0 ILOAD 1A/div 0 0 1.8 VOUT 2V/div 1.6 VOUT (2V/div) 1.4 VIN = 5V, 12V 1.2 VGATE (2V/div) 0 0 1.0 10 35 60 85 200s/div CBOARD = 470F, RSENSE = 100m, CGATE = 22nF, RS = 0 50s/div CBOARD = 470F, RSENSE = 100m, CGATE = 0 TEMPERATURE (C) MAX4273 TURN-OFF TIME (CBOARD = 470F) MAX4273 TURN-OFF TIME (EXTERNAL CGATE = 22nF, CBOARD = 470F) ON COMPARATOR THRESHOLD vs. INPUT VOLTAGE MAX4271/3-20b MAX4271/3-20a 0.605 ON ON VGATE 2V/div ILOAD 1A/div MAX4271/3-21 -15 VGATE 2V/div ILOAD 1A/div 0 0 VOUT 2V/div VOUT 2V/div 0 0 ON COMPARATOR THRESHOLD (V) -40 0.603 RISING 0.601 FALLING 0.599 0.597 0.595 50s/div 20s/div 0 2 4 6 8 10 12 14 VIN (V) UVLO THRESHOLD VOLTAGE vs. TEMPERATURE } } 0.6000 VIN = 3V 0.5975 155 RISING UVLO DELAY (ms) VIN = 5V 0.6025 2.55 UVLO THRESHOLD (V) VIN = 12V 0.6050 UVLO DELAY vs. TEMPERATURE 2.50 2.45 FALLING 2.40 -40 -15 10 35 TEMPERATURE (C) 60 85 VIN = 5V, 12V VIN = 3V 150 145 2.35 2.30 0.5950 160 MAX4271/3-26 2.60 MAX4271/3-22 0.6075 FALLING RISING ON COMPARATOR THRESHOLD (V) 0.6100 MAX4271/3-27 ON-COMPARATOR THRESHOLD vs. TEMPERATURE 140 -40 -15 10 35 TEMPERATURE (C) 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) _______________________________________________________________________________________ 7 MAX4271/MAX4272/MAX4273 Typical Operating Characteristics (continued) (VIN = 5V, RSENSE = 100m, CBOARD = 47F, TA = +25C, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = 5V, RSENSE = 100m, CBOARD = 47F, TA = +25C, unless otherwise noted.) INC THRESHOLD vs. INPUT VOLTAGE FALLING 0.595 0.575 1.2038 RISING 612 610 608 FALLING 6 8 10 12 14 1.2034 1.2032 1.2030 1.2028 1.2026 1.2024 602 1.2022 16 1.2020 -40 -15 INPUT VOLTAGE (V) 10 35 60 85 3 5 7 TEMPERATURE (C) 1.2035 950 CTIM = 100nF 945 RETRY TIMEOUT (ms) 1.2030 1.2025 1.2020 1.2015 940 935 930 1.2010 925 1.2005 920 1.2000 -40 -15 10 35 60 5 7 9 11 13 INPUT VOLTAGE (V) RETRY TIMEOUT PERIOD vs. TEMPERATURE STARTUP TIME (CBOARD = 470F) 15 MAX4271/3-34 MAX4271/3-33 990 RETRY PERIOD (ms) 3 85 TEMPERATURE (C) 995 12V ON VGATE 2V/div ILOAD 1A/div 985 980 VOUT 2V/div 5V 975 970 3V 965 -40 -15 10 35 TEMPERATURE (C) 8 11 RETRY TIMEOUT PERIOD vs. INPUT VOLTAGE MAX4271/3-31 1.2040 9 INPUT VOLTAGE (V) REFERENCE VOLTAGE vs. TEMPERATURE REFERENCE VOLTAGE (V) 1.2036 604 600 4 MAX4271/3-30 MAX4271/3-29 614 606 0.585 1.2040 MAX4271/3-32 0.605 616 THRESHOLD (mV) 0.615 618 REFERENCE VOLTAGE (V) RISING MAX4273 REFERENCE VOLTAGE vs. INPUT VOLTAGE INC THRESHOLD vs. TEMPERATURE 620 MAX4271/3-28 0.625 THRESHOLD (V) MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection 60 85 500s/div CBOARD = 470F, RSENSE = 100m, CTIM = 10nF, CGATE = 0 _______________________________________________________________________________________ 13 15 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection (VIN = 5V, RSENSE = 100m, CBOARD = 47F, TA = +25C, unless otherwise noted.) STARTUP TIME (CBOARD = 0) TURN-OFF TIME (CBOARD = 0) MAX4271/3-35 MAX4271/3-37 ON VGATE 2V/div ON VGATE 2V/div ILOAD 1A/div 0 VOUT 2V/div VOUT 2V/div 0 100s/div CBOARD = 0, RSENSE = 100m, CTIM = 10nF, CGATE = 0 50s/div CBOARD = 0, RSENSE = 100m, CGATE = 0, RS = 0 Pin Description PIN MAX4271 MAX4272 MAX4273 FUNCTION NAME Current-Sense Threshold Setting Input. Connect a resistor from RTH to VIN to set the fast comparator threshold. Bypass to VIN with 0.1F. Connect RTH to VIN to disable both the fast comparator and current regulation at startup. Short RTH to GND for a 200mV threshold. See Fast Comparator Threshold section. -- 1 RTH -- 2 AUXVCC 1 3 IN 2 4 SENSE Current-Sense Resistor Voltage Input. RSENSE is connected from IN to SENSE. 3 5 GATE Gate Drive Output. Connect to gate of external N-channel pass transistor. -- 6 -- 7 LLMON 4 8 GND Ground CEXT Auxiliary Supply Input. Supply input for short-circuit switchover. To use this, connect a 1F capacitor from AUXVCC to GND; otherwise, leave floating. See Auxiliary VCC section. Input Voltage. Connect to +2.7V to +13.2V supply; 15V absolute maximum voltage rating. External Gate Capacitance Connection. Connect a capacitor from CEXT to GATE to increase the gate charging time. This pin goes high impedance during a fast comparator fault for fast discharge. Load Line Monitor. Connect to the source of the external N-channel MOSFET. The external FET is turned on only when the load voltage is less than 100mV. -- 9 CTON Startup Timer Input. Leave floating or connect the timing capacitor from CTON to GND. See Startup and Retry Timers section. 5 10 CSPD Slow Comparator Speed Setting. Leave floating or connect the timing capacitor from CSPD to GND. See Slow Comparator Response Time section. _______________________________________________________________________________________ 9 MAX4271/MAX4272/MAX4273 Typical Operating Characteristics (continued) MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection Pin Description (continued) PIN MAX4271 MAX4272 MAX4273 FUNCTION NAME 6 11 CTIM Startup and Retry Timers Input. Controls the startup time and the autoretry time (32x startup time) in the MAX4272, only the autoretry time in the MAX4273, and only the startup time in the MAX4271. Leave floating or connect the timing capacitor from CTIM to GND. Connect to IN for latched mode (this prevents autoretry in MAX4273). See Startup and Retry Timers section. 7 12 STAT Status Output. High indicates startup completed with no fault (Table 1). STAT is an open-drain output. ON Comparator Input. Connect high for normal operation; connect low to force the MOSFET off. Comparator threshold VTH,ON = 0.6V allows for precise control over shutdown feature. Pulse ON low for 20s min to unlatch after a fault (MAX4273 in latched mode, or MAX4271). Negative pulses are ignored during autoretry (MAX4273 in autoretry mode, or MAX4272). See ON and Reset Comparators section. 8 13 ON -- 14 REF 1.2V Reference Output. Do not bypass with a capacitor to GND. -- 15 INC Uncommitted Comparator Input. Controls OUTC. -- 16 OUTC Uncommitted Comparator Output. OUTC goes high 150ms after INC goes high. OUTC goes low immediately after INC goes low. OUTC is an open-drain output. Detailed Description The MAX4271/MAX4272/MAX4273 are circuit breaker ICs designed for hot-swap applications where a line card is inserted into a live backplane. Normally, when a line card is plugged into a live backplane, the card's discharged filter capacitors provide a low impedance that can momentarily cause the main power supply to collapse. The MAX4271/MAX4272/MAX4273 are designed to reside either in the backplane or in the removable card to provide inrush current limiting and short-circuit protection. This is achieved by using an external N-channel MOSFET, an external current-sense resistor, and two on-chip comparators. Figures 1 and 2 show the functional diagrams. The timing and voltage levels for several critical parameters can be adjusted with external resistors, external capacitors, or by pin strapping. The timing components are optional; without them, the part is set to its nominal values, as shown in the Electrical Characteristics. The parameters that can be adjusted are: * Current-limit threshold * Slow comparator response time * Startup timer * Autoretry timeout period (time the part is shut down after an overcurrent event) * Fault management (latched/autoretry) * Current overload threshold Startup Mode CTIM (MAX4271/MAX4272) or CTON (MAX4273) sets the startup period (see Startup and Retry Timers). The startup period begins after three conditions are met: 1) 150ms after VIN exceeds the UVLO threshold (see Over/Undervoltage Lockouts) AND 2) 10s after VON >0.6V AND 3) The device is no longer in retry mode. During startup, the slow comparator is disabled and the inrush current can be limited in two ways: 1) Slow ramping of the current to the load by controlling the external MOSFET gate voltage OR 2) Limiting the current to the load by regulating the voltage across the external current-sense resistor * Fast comparator threshold 10 ______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection MAX4271/MAX4272/MAX4273 CSPD VIN CSPD IN 6A MAX4271 MAX4272 2.45V 6A VSC,TH 50mV SLOW COMPARATOR RSENSE INPUT UVLO VSC,TH 200mV FAST COMPARATOR 150ms DELAY ON VIN RISING SENSE GATE DRIVE DISCHARGE STAT CHARGE PUMP (1MHz) ENABLE VIN LOGIC CONTROL 0.1V 4A M1 GATE N GATE OVLO CTIM ON ON COMPARATOR CTIM 0.6V VOUT GND Figure 1. MAX4271/MAX4272 Functional Diagram Unlike other circuit breaker ICs, the MAX4271/ MAX4272/MAX4273 regulate the current to a preset level instead of completely turning off the external N-FET if an overcurrent condition occurs during startup. In startup mode, the gate drive current is limited to 100A and decreases with the increase of the gate voltage (see Gate Charge Current vs. Gate Voltage in the Typical Operating Characteristics). This allows the controller to slowly enhance the MOSFET. If the fast comparator detects an overcurrent, the gate voltage is momentarily discharged with a fixed 70A current until the load current through the sense resistor (RSENSE) decreases below its threshold point. This effectively regulates the inrush current during startup. Figure 3 shows the startup waveforms. STAT goes high at the end of the startup period if no fault condition is present. Normal Operation (DualSpeed/BiLevel) In normal operation (after the startup timer has expired), protection is provided by turning off the external MOSFET when a fault condition is encountered. DualSpeed/BiLevel fault protection incorporates two comparators with different thresholds and response times to monitor the current: 1) Slow comparator. This comparator has an externally set response time (from 20s to seconds) and a fixed 50mV threshold voltage. The slow comparator ignores low-amplitude momentary current glitches. After an extended overcurrent condition, a fault is generated and the MOSFET gate is slowly discharged. 2) Fast comparator. This comparator has a fixed 350ns response time and a 200mV threshold voltage (adjustable from 50mV to 750mV in MAX4273). The fast comparator turns off the MOSFET immediately after it detects a large amplitude event such as a short circuit. ______________________________________________________________________________________ 11 MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection CSPD VIN AUXVCC IN VIN 2.45V VFC,TH = 50mV 6A MAX4273 6A REF INPUT UVLO REF 1.2V 150ms DELAY ON VIN RISING RSENSE RTH VFC,TH = 200mV SLOW COMPARATOR RTH FAST COMPARATOR VFC,TH = 50mV TO 750mV 10A AUXVCC SENSE CEXT CEXT AUXVCC DISCHARGE ENABLE STAT CHARGE PUMP 1MHz 0.1V VIN LOGIC CONTROL Q1 GATE DRIVE 0.1V 4A GATE N GATE OVLO OUTPUT OVLO LLMON CTIM CTIM VIN 4A ON ON COMPARATOR CTON 0.6V CTON RESET COMPARATOR OUTC 150ms DELAY ON INC RISING INC 0.6V VOUT GND Figure 2. MAX4273 Functional Diagram 12 ______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection BiLevel Fault Protection Slow Comparator The slow comparator is disabled at startup while the external MOSFET is turning on. This allows the part to ignore the higher-than-normal inrush current charging the board capacitors when a card is first plugged in. If the slow comparator detects an overload condition while in normal operation (after startup is completed), it turns off the external MOSFET by discharging the gate capacitance with a 200A current. The slow comparator threshold is set at 50mV and has a default delay of 20s (CSPD floating), allowing it to ignore power-supply glitches and noise. The response time can be lengthened with an external capacitor at CSPD (Figure 10). If the overcurrent condition is not continuous, then the duration above the threshold minus the duration below must be greater than 20s (or the external programmed value) for the device to trip. When the current is above the threshold, CSPD is charged with a 6A current source. A fault is detected when CSPD is charged to the trip point of 1.2V. Therefore, a pulsing current with a duty cycle of 50% or greater (i.e., the current is above the threshold level > 50% of the time) is considered a fault condition even if it is never higher than the threshold for longer than the slow comparator's set response time. The discharge rate depends on the N-FET gate capacitance and the external capacitance at GATE. In the MAX4273, CEXT remains connected and capacitance to this point has to be discharged by the same current. This increases the discharge time. Once the fault condition is detected, the STAT pin goes low and the device goes into retry or latched mode. Fast Comparator The fast comparator behaves differently according to the operating mode. During startup, the fast comparator is part of a simple current regulator. When the sensed current is above the fast comparator threshold, the gate is discharged with a 70A current source. When the sensed current drops below the threshold, the charge pump turns on again. The sensed current will rise and fall near the threshold due to the fast comparator and charge-pump propagation delay. The gate voltage will be roughly sawtooth shaped, and the load current will present a 20% ripple. The ripple can be reduced by adding a capacitor from GATE to GND. STAT ON STAT tSTART VGATE VGATE 2.7V TO 6V 2.7V TO 6V VOUT VOUT VTH VGATE VOUT CBOARD = LARGE IFAST, SET ILIM CBOARD = 0 ILOAD ILOAD tON Figure 3. Startup Waveforms tOFF Figure 4. Response to a Fault Condition ______________________________________________________________________________________ 13 MAX4271/MAX4272/MAX4273 In each case, when a fault is encountered, the status pin (STAT) goes low, and for the MAX4273, the device discharges the output voltage through a 1k resistor from LLMON to GND. After a fault, the MAX4271 stays latched off and the MAX4272 enters retry mode, while the MAX4273 has selectable latched or retry mode. Figure 4 shows the waveforms of a fault condition. MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection If the sensed current is still high after the startup timer expires, the MOSFET gate is discharged completely as described below. In normal operation (after startup), the fast comparator is used as an emergency off switch. If the load current reaches the fast comparator threshold, the device quickly forces the MOSFET off completely. This could happen in the event of a serious current overload or a dead short. The fast comparator has a 350ns response time and discharges GATE with a 1mA current. Given a 1000pF gate capacitance and 12V gate voltage, the MOSFET will be off in about 12s. Any additional capacitance connected between GATE and GND to slow down the startup time also increases the turn-off time. In the MAX4273, CEXT goes high impedance during the fast discharge. This reduces the effective capacitance on GATE if a capacitor is used between GATE and CEXT, and allows the MOSFET to quickly turn off. In turn, this allows adjustment of the MOSFET charging time without affecting the fast discharge rate, although it does affect the slow discharge rate. The MAX4271/MAX4272 fast comparator threshold is set to four times the slow comparator threshold (i.e., 200mV). The MAX4273 fast comparator threshold is set to 200mV by connecting RTH to GND, is disabled by connecting RTH to IN, or is adjustable by an external resistor connected to IN (see Fast Comparator Threshold (RTH)). Latched/Autoretry The MAX4271 MOSFET driver stays latched off after a fault condition until it is reset by a negative-going pulse on the ON pin. The MAX4272 is periodically turned on after a fault condition with a timeout duration set by an external timing capacitor on CTIM. The MAX4273 has a selectable latched mode or retry mode. Connect CTIM to IN to set the device in latched mode, or use an external capacitor at CTIM to set the retry timeout. Pulse ON low for 20s (min) to restart after a fault (MAX4271/MAX4273 in latched mode). Negative pulses are ignored during autoretry (MAX4273 in autoretry mode, or MAX4272). The capacitor on CTIM affects the MAX4272's retry timeout period (time the part is shut down after an overcurrent event) and the startup time (see the Electrical Characteristics). The retry timeout period is fixed at 32 times the startup time in order to minimize power dissipation in the external MOSFET in case of a short-circuit condition (see MOSFET Thermal Considerations). This is not an issue for parts latched off during a fault condition since they stay off until commanded on. The MAX4273 configured in retry mode has a separate startup timer capacitor (CTON) and retry timeout capacitor (CTIM). This allows the user to change the ratio between startup time and retry timeout period. Status Output The status output is an open-drain output that goes low under the following conditions: * During the UVLO delay period * In startup * Forced off (ON <0.6V) * In an overcurrent condition * In the retry timeout period (or latched off, for the latched parts) STAT is high only if the part is in normal mode and no faults are present (Table 1). Figure 5 shows the status (STAT) output timing diagram. Over/Undervoltage Lockouts The UVLO prevents the MAX4271/MAX4272/MAX4273 from turning on the external MOSFET until VIN exceeds the lockout threshold (2.25V min) for 150ms. The UVLO protects the external MOSFET from insufficient gate drive voltage. The 150ms timeout ensures that the board is fully plugged into the backplane and that VIN Table 1. Status Output Truth Table PART IN STARTUP ON PIN OVERCURRENT CONDITION PART IN RETRY-TIMEOUT PERIOD (OR LATCHED OFF DUE TO OVERCURRENT CONDITION) STAT PIN (STATUS) Yes X X X X Low X Yes X X X Low X X Low X X Low X X X Yes X Low X X X X Yes Low No No High No No High IN UVLO DELAY PERIOD 14 ______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection A large board capacitance or a short startup period may prevent the MAX4272 from charging completely in one startup period. The MAX4272 responds to these conditions by charging the capacitor with bursts defined by a tON duty cycle and a period of tON + tRETRY. The charging will be complete after several retries unless the resistive load or current load excessively discharges the board capacitance during the retry timeout. This feature applies to the MAX4273 if LLMON is left floating or is connected to GND. To prevent multiple charging bursts, ensure that the tON timer exceeds the minimum time required to complete the charge of the board capacitance (see Component Selection). Applications Information Component Selection N-Channel MOSFET Select the external N-channel MOSFET according to the application's current level. Table 2 lists some recommended components. The MOSFET's on-resistance (RDS(ON)) should be chosen low enough to have a minimum voltage drop at full load to limit the MOSFET power dissipation. High RDS(ON) can cause output ripple if the board has pulsing loads or triggers an external undervoltage reset monitor at full load. Determine the device power-rating requirement to accommodate a short circuit on the board at startup with the device IN RSENSE MAX4271 MAX4272 SENSE VGD GATE GATE DRIVE CHARGE PUMP VGS Gate Overvoltage Protection New-generation MOSFETs have an absolute maximum rating of 8V for the gate-to-source voltage (VGS). To protect these MOSFETs, the MAX4271/MAX4272 limit the gate-to-drain voltage (the MAX4273 limits the gate-tosource voltage) to +7.5V with an internal zener diode. No protection is provided for negative V GS (MAX4271/ MAX4272). If GATE can be discharged to ground faster than the output voltage, an external small-signal protection diode (D1) can be used, as shown in Figure 6. The MAX4273 has the protection diode internal. ON VOUT D1 CBOARD Figure 6. External Gate-Source Protection Table 2. Recommended N-Channel MOSFETs PART NUMBER VIN O IRF7401 1.2V CTIM (CTON)* O VIN MMSF3300 MMSF5N02H NO FAULT CONDITIONS PRESENT 20m, 8 SO, 30V Motorola MTB60N05H *MAX4273 ONLY NDS8426A FDB8030L 22m, 8 SO, 20V 6m, D2PAK, 20V 30m, 8 SO, 20V 14m, D2PAK, 50V FDS6670A O DESCRIPTION 11m, 8 SO, 30V International Rectifier IRL3502S FAULT CONDITION, OR ON FALLING EDGE STAT MANUFACTURER IRF7413 tSTART M1 N 10m, 8 SO, 30V Fairchild 13.5m, 8 SO, 20V 4.5m, D2PAK, 30V Figure 5. Status (STAT) Output Timing Diagram ______________________________________________________________________________________ 15 MAX4271/MAX4272/MAX4273 is stable. Any input voltage transient at IN below the UVLO threshold will reset the device and initiate a startup sequence. These devices also have an overvoltage lockout (OVLO) feature that prevents the device from restarting after a fault condition if the discharge has not been completed. VGATE has to be discharged to below 0.1V. Additionally, the MAX4273 LLMON pin discharges the load line with a 1k pulldown and prevents startup until the load voltage is below 0.1V. Since the MAX4271/MAX4272 do not monitor the output voltage, a startup sequence can be initiated while the board capacitance is still charged. MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection configured in automatic retry mode (see MOSFET Thermal Considerations). Using the MAX4271/MAX4273 in latched mode allows the consideration of MOSFETs with higher RDS(ON) and lower power ratings. A MOSFET can typically withstand single-shot pulses with higher dissipation than the specified package rating. Low MOSFET gate capacitance is not necessary since the inrush current limiting is achieved by limiting the gate dv/dt. Table 3 lists some recommended manufacturers and components. Sense Resistor The slow comparator threshold voltage is set at 50mV. Select a sense resistor that causes a 50mV voltage drop at a current level above the maximum normal operating current; typically, set the overload current at 1.2 to 1.5 times the nominal load current. The fast comparator threshold is typically set at 200mV. This will set the fault current limit at four times the overload current limit. The MAX4273 fast comparator threshold can be set between 50mV and 750mV; see Table 4 for a detailed listing. Choose the sense resistor power rating according to the device configuration. If no retry mode is selected, PRSENSE = (IOVERLOAD)2 x RSENSE; if retry is selected, then PRSENSE = (IFAULT)2 x RSENSE x (tON/tRETRY). Fast Comparator Threshold (RTH) (MAX4273) The fast comparator threshold is determined by the external resistor connected at RTH. To select threshold voltages between 50mV and 750mV, use resistor values between 5k and 75k according to Figure 7. Resistor values between 200 and 5k are not recommended. Setting the threshold voltage of the fast comparator below 50mV will effectively override the slow comparator operation. The MAX4273 fast comparator can be disabled by shorting the RTH pin to VIN (VIN 25mV or less). Ground RTH to set the threshold to 200mV internally. Startup and Retry Timers (CTIM, CTON) The startup (tSTART) and retry (tRETRY) timers are determined by the capacitors connected at CTIM and CTON. The capacitor connected to CTIM has two functions for the three devices as follows: DEVICE CTIM FUNCTION MAX4271 Startup time MAX4272 Startup time and sets retry timer MAX4273 Sets retry timer Table 3. Component Manufacturers COMPONENT MANUFACTURER Sense Resistors MOSFETS PHONE WEB Dale-Vishay 402-564-3131 IRC 704-264-8861 www.vishay.com www.irctt.com Fairchild 888-522-5372 www.fairchildsemi.com International Rectifier 310-322-3331 www.irf.com Motorola 602-244-3576 www.mot-sps.com/ppd/ Table 4. Current Levels vs. RSENSE RSENSE (m) 10 50 100 16 PART NUMBER OVERLOAD THRESHOLD SET BY SLOW COMPARATOR (A) FAULT CURRENT THRESHOLD SET BY FAST COMPARATOR (A) MAX4271/MAX4272 5 20 MAX4273 5 5 to 75 MAX4271/MAX4272 1 4 MAX4273 1 1 to 15 MAX4271/MAX4272 0.5 2 MAX4273 0.5 0.5 to 7.5 ______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection FAST COMPARATOR THRESHOLD VOLTAGE vs. RTH 800 RTH (k) = VTH,FC (mV)/10 700 VTH, FC (mV) 600 500 400 DISABLED FOR RTH < 200 300 200 INDETERMINATE, NOT RECOMMENDED FOR RTH < 5k 100 0 0 10 20 30 40 50 60 70 80 RTH (k) Figure 7. Fast Comparator Threshold vs. RTH Case A. Startup Without Current Regulation There are three ways to turn on the MOSFET without reaching the fast comparator current limit: 1) If the board capacitance is small, the inrush current is low. 2) If the gate capacitance is high, the MOSFET turns on slowly. 3) The fast comparator can be disabled (MAX4273 only). In all three cases, tON is determined only by the charge required to enhance the MOSFET. Effectively, the small gate-charging current limits the output voltage dv/dt. This time can be extended by connecting an external capacitor between GATE and GND (MAX4271/ MAX4272) (Figure 9) or between GATE and CEXT (MAX4273). The turn-on time is dominated by the external gate capacitance if this value is considerably higher than the MOSFET gate capacitance. Table 6 shows the timing required to enhance the recommended MOSFET with or without the external capacitor; Figure 3 shows the related waveforms and timing diagrams. (See Time to Charge Gate vs. C GATE and Startup Time with CBOARD = 0 in the Typical Operating Characteristics.) Remember that a high gate capacitance also increases the turn-off time (t OFF ), except in the case of a MAX4273 fast fault. If an external gate capacitor is not used, RS is not necessary. RS prevents MOSFET self-oscillations that can occur when CGATE is high while CBOARD is low. Electrical characteristics as specified by the manufacturer's data sheet are: FDS6670A: CISS = 3200pF, QT(MAX) = 50nC, RDS(ON) = 8.2m IRF7401: CISS = 1600pF, QT(MAX) = 48nC, RDS(ON) = 22m MMSF5N03HD: C ISS = 1200pF, Q T (MAX) = 21nC, RDS(ON) = 40m Table 5. Startup and Retry Timing Parameters PART tON DEFAULT (s) EXTERNALLY SET tRETRY DEFAULT (s) EXTERNALLY SET MAX4271 10 tON (ms) = 0.31 x CTIM (nF) MAX4272 10 tON (ms) = 0.31 x CTIM (nF) 320 tRETRY (ms) = 32 x tON = 10 x CTIM (nF) No retry available MAX4273* 10 tON (ms) = 0.31 x CTON (nF) 320 tRETRY (ms) =10 x CTIM (nF) *MAX4273 retry feature disabled by connecting CTIM to VIN. ______________________________________________________________________________________ 17 MAX4271/MAX4272/MAX4273 CTON determines the maximum time allowed to complete turn-on for the MAX4273. The default values for turn-on time (tON) and tRETRY are chosen by leaving these pins floating; they are 10s and 320s, respectively. These are also the minimum values (not controlled and dependent on stray capacitance). Longer timings are determined by the size of the capacitor according to Figure 8, and can be determined in Table 5, which lists the startup and retry timing parameters. Set the tON timer long enough to allow for the MOSFET to be enhanced and the load capacitor to be charged completely . There are two ways of completing the startup sequence. Case A describes a startup sequence that does not use the current-limiting feature and slowly turns on the MOSFET by limiting the gate dv/dt. Case B uses the currentlimiting feature and turns on the MOSFET as fast as possible while still preventing a high inrush current. Table 6. "No-Overcurrent" Turn-On Timing (Startup Without Current Limit) DEVICE CGATE (nF) VIN = 3V VIN = 5V VIN = 12V VIN = 3V VIN = 5V VIN = 12V 0 0.22 0.16 0.19 0.07 0.13 0.145 Fairchild FDS6670A International Rectifier IRF7401 Motorola MMSF5N03HD MOSFET tON (ms) MOSFET tOFF (ms) 22 2.3 2 3.2 0.54 1.1 1.95 0 0.175 0.130 0.16 0.075 0.13 0.16 22 1.9 1.8 3.5 0.54 1.1 2.0 0 0.101 0.074 0.073 0.033 0.067 0.085 22 2.0 1.8 3.2 0.470 1.0 1.95 RSENSE VOUT M1 VIN tON AND tRETRY vs. CTON AND CTIM CBOARD 10,000 tRETRY vs. CTIM (MAX4272/MAX4273) RS* 1000 tON AND tRETRY (ms) MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection RPULLUP 100 IN STAT SENSE GATE CGATE 10 ON 1 CSPD 0.01 tON vs. CTIM (MAX4271/MAX4272) tON vs. CTON (MAX4273) 0.1 0.01 0.1 1 10 100 1000 MAX4271 MAX4272 MAX4273 CTIM GND CSPD CTIM CAPACITANCE (nF) *OPTIONAL (SEE TEXT) Figure 8. Startup and Retry Timeout Figure 9. Operation with an External Capacitor Case B. Startup With Current Regulation ed current ripple but increases tOFF by increasing the gate delay (td) (Figure 4). The actual startup time is determined by the longer of the two timings of Case A and Case B. Set the startup timer tSTART at 2 tON to guarantee enough time for the output voltage to settle; also take into consideration device parameter variation. In applications where the board capacitance (CBOARD) at VOUT is high, the inrush current causes a voltage drop across RSENSE that exceeds the fast comparator threshold (VFC,TH). In this case, the current charging CBOARD can be considered constant and the turn-on time is determined by: tON = CBOARD VIN / IFAST,SET where the maximum load current IFAST,SET = VFC,TH / RSENSE. Figure 3 shows the waveforms and timing diagrams for a startup transient with current regulation. (See Startup Time (CBOARD = 470F) in the Typical Operating Characteristics.) When operating under this condition, an external gate capacitor is not required. Adding an external gate capacitor at GATE to GND reduces the regulat- 18 Retry The retry timer defines the dead time before the IC tries to restart a startup sequence following a fault detection. This feature is available on the MAX4272/MAX4273. Before selecting the retry timer value, determine how long a temporary high-current fault condition may be present. In the event of a permanent fault, the automatic retry will effectively force current pulses through the ______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection Additional External Gate Capacitance (CEXT) An external gate capacitance can be connected at GATE. This increases the time required to enhance the MOSFET and further limits the output rise time. In the MAX4271/MAX4272, connect the external capacitor between GATE and GND. In the MAX4273, the external capacitor can be connected between GATE and CEXT or GND. If the capacitor is connected to CEXT, it is discharged to ground during a slow comparator fault but it is left floating during a fast comparator fault; this allows the device to turn off the external MOSFET faster during critical faults. (CEXT is biased at VIN; therefore, use a nonpolarized capacitor). Capacitance connected from GATE to CEXT does little to decrease the regulated current ripple. Add a small capacitor (5nF) from GATE to GND. See the charging and discharging time vs. CGATE graphs in the Typical Operating Characteristics. Slow Comparator Response Time (CSPD) The slow comparator threshold is set at 50mV, and its response time is determined by the external capacitor connected to CSPD (Figure 10). A minimum response time of 20s (typ) is achieved by leaving this pin floating. This time is determined internally and is not affected by stray capacitance at CSPD (up to 100pF). Set the slow comparator response time to be longer than the normal operation load transients (see Slow Comparator). ON and Reset Comparators The ON comparator controls the ON/OFF function of these devices. The ON comparator is a precision voltage comparator that can be used for temperature monitoring or as an additional UVLO (Figure 11). The MAX4273 also features an uncommitted delayed comparator. This comparator can be used for voltage monitoring, power sequencing, or for generating a power-on reset signal for on-card microprocessors (Figure 12). Both comparator threshold voltages are set at VREF/2 = 0.6V with a 3mV (typ) hysteresis. The uncommitted comparator OUTC output is an opendrain output, and it is asserted low when its input voltage (INC) is below the threshold voltage. It goes into a high-impedance state 150ms after the voltage has risen above the threshold. The delay for negative-going edges is 10s. Figure 13 shows the MAX4273 used to monitor precisely the temperature of an external device such as the MOSFET. This configuration uses the uncommitted comparator to set the UVLO at a higher level by running its output into the ON comparator's input. The ON comparator initiates startup when its input voltage (VON) rises above the threshold voltage and turns off the MOSFET when the voltage falls below the threshold. The propagation delay is 10s going high or low. The ON comparator is also used to reset the MAX4271/MAX4273 (when CTIM = V IN) after a fault condition (see Latched/Autoretry). SLOW COMPARATOR RESPONSE TIME vs. CSPD VREF MAX4271 MAX4272 MAX4273 1000 R1 RESPONSE TIME (ms) 100 ON tCSPD (ms) = 0.2 x CSPD (nF) LOGIC CONTROL 10 NTC 1 R2 0.6V 0.1 0.01 0.01 0.1 1 10 100 1000 CSPD (nF) Figure 10. Slow Comparator Response Time vs. CSPD R1 = R2 (VREF / O.6 - 1) R2 = VALUE OF THE NTC RESISTOR AT THE LIMIT TEMPERATURE VREF = ANY REFERENCE VOLTAGE AVAILABLE OR VIN Figure 11. Temperature Monitoring and Protection ______________________________________________________________________________________ 19 MAX4271/MAX4272/MAX4273 MOSFET with a duty cycle equal to tON/tRETRY and with a current equal to IFAST,SET. Therefore, particular care has to be taken when choosing between immediate retry and board space needed to manage the power dissipation capabilities of the MOSFET (see Thermal Considerations). The duty cycle is fixed to 1/32 for the MAX4272, but can be varied in the MAX4273 by choosing CTIM and CTON independently. MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection VIN BACKPLANE REMOVABLE CARD VCC IN SENSE 10k GATE LLMON P INC SENSE GATE IN MAX4273 OUTC RESET ON MAX4271 MAX4272 MAX4273 Figure 12. Power-On Reset VOUT VIN RESET 1M NTC IN SENSE INC GATE REF MAX4273 ON OUTC GND Figure 14. Fail-Safe Connector LLMON gate drive until the MOSFET is turned off and the main supply recovers. The 1F capacitor is charged from VIN through an internal switch during normal operation. Maximum Load Capacitance Figure 13. Power-On Reset and Temperature The ON and INC comparator inputs and the STAT and OUTC can be pulled to voltages up to 14V independently of VIN, thus allowing parts to be daisy-chained and not be turned on through the internal protection diodes. In some applications, it is useful to use connectors with staggered leads. In Figure 14, the ON pin forces the removable board to be powered up only when all connections are made. Auxiliary VCC The auxiliary VCC is available on the MAX4273 and is used to sustain the input voltage required for the device to operate during a short-circuit condition on the board. When a short occurs, the main system power supply could collapse and the MAX4273 will not have enough voltage to keep the gate drive operational and turn off the external MOSFET. If the fault is not removed, the system could remain in a sustained short-circuit state. Connect a 1F capacitor from the AUXVCC pin to GND. This capacitor will deliver the necessary energy to the 20 The MAX4271/MAX4272/MAX4273 can be used on the backplane to regulate current upon insertion of a removable card (Figure 16). This allows multiple cards with different input capacitance to be inserted into the same slot even if the card doesn't have on-board hotswap protection. The MAX4271/MAX4272/MAX4273 current-limiting feature is active during the startup period set by CTIM. The startup period can be triggered if VIN is connected to ON through a trace on the card. Once tSTART has expired (timed out), the load capacitance has to be charged or a fault condition is detected. To ensure startup with a fixed CTIM, tSTART has to be longer than the time required to charge the board capacitance. The maximum load capacitance is calculated as follows: CBOARD < tSTART IFAST,SET / VIN Input Transients The voltage at VIN must be above the UVLO during inrush and fault conditions. When a short condition occurs on the board, the fault current can be higher than the fast comparator current limit. The gate voltage ______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection MAX4271/MAX4272/MAX4273 VIN 100k IN * * * * * * SENSE GATE ON LLMON P INC MAX4273 OUTC RESET Figure 15. Adjustable Undervoltage Lockout and Output Voltage Reset Generator is discharged immediately, but note that the MOSFET is not completely off until VGS < VTH. If the main system power supply collapses below UVLO, the MAX4271/ MAX4272/MAX4273 will force the device to restart in startup mode with a 150ms delay once the supply has recovered. The main system power supply must be able to deliver this fault current without excessive voltage drop. The MOSFET is turned off in a very short time; therefore, the resulting dv/dt can be considerable. The backplane delivering the power to the external card must have a fairly low inductance to limit the voltage transients caused by the removal of a fault. Bypassing the input with a small capacitor alleviates false UVLO trips due to these transients. BACKPLANE REMOVABLE CARD WITH NO HOT-INSERTION PROTECTION VOUT VIN IN CTIM SENSE MAX4271 MAX4272 MAX4273 GATE CBOARD ON MOSFET Thermal Considerations During normal operation, the MOSFET dissipates little power, it is fully turned on, and its RDS(ON) is minimal. The power dissipated in normal operation is P D = ILOAD2 x RDS(ON). A considerable amount of power is dissipated during the startup and turn-off transients. The design must take into consideration the worst-case scenario of a continuous short-circuit fault present on the board. Two cases need to be considered: 1) The single turn-on with the device latched after a fault (when using MAX4271 or MAX4273 in latched mode) 2) The continuous automatic retry (when using the MAX4272 or MAX4273 in retry mode) Use the following equation to calculate the maximum transient thermal resistance (in C/W) required for an output short to ground: ZJA (max) = (TJMAX - TA) / (VIN IFAST, SET) Figure 16. Using the MAX4271/MAX4272/MAX4273 on a Backplane MOSFET manufacturers typically include curves for the transient thermal resistance, Z JA , of the package (Figure 17). Find the thermal impedance of the MOSFET by using t START as the pulse duration and by choosing the single pulse curve for latched mode parts or by choosing the duty cycle = 0.03 curve for the MAX4272 (the duty cycle is fixed at 32:1). If the ZJA required is less than that of the package, reduce tSTART, reduce IFAST,SET, use a heatsink on the MOSFET, or choose one with better thermal characteristics. ______________________________________________________________________________________ 21 100 D = 0.50 THERMAL RESPONSE (ZJA) MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection 10 0.20 0.10 0.05 PDM 0.02 1 0.01 t1 SINGLE PULSE (THERMAL RESPONSE) t2 NOTES: 1. DUTY FACTOR D = t1 / t2 2. PEAK TJ = PDM X ZJA + TA 0.1 0.0001 0.001 0.01 0.1 1 10 100 t1, RECTANGULAR PULSE DURATION (s) Figure 17. Example Curves (from IRF7413A) for Maximum Effective Transient Thermal Impedance, Junction to Ambient For the MAX4273 in retry mode, the duty cycle can be adjusted. Use the MOSFET ZJA curve and the tSTART pulse duration to choose a maximum duty cycle, D. Calculate the retry time: tRETRY = tSTART / D Use Figure 8 to determine CTIM given tRETRY. Design Procedure (MAX4273) GIVEN: * Hot-swap 5V supply to a 1000F card * MOSFET IRF7413A: RDS(on) = 0.0135 * Operating current = 4A The MOSFET pulsed drain current limit is 58A. Another consideration for setting the current limit is the system requirement. Systems may glitch if 58A load transients are present. For this example, the load transient will be limited to 10A: System current limit = 10A Current-sense resistor = 10m Fast comparator threshold = 10m 10A = 100mV Select RTH from Figure 7, RTH = 10k 3) Set Startup timer. Startup current = System current limit = 10A * Overload current = 5A VIN = 5V * System current limit = 10A CBOARD = 1000F * Retry enabled tON = 1000F 5V / 10A = 500s PROCEDURE: Give a factor of 2 guardband on the startup timer. 1) Select the current sense resistor: tSTART = 2 tON = 1.0ms Slow comparator threshold = 50mV Overload current = 5A Current-sense resistor value = 50mV/5A = 10m VIN = 5V. The device will initiate a slow fault if the load current is greater than 5A for longer than 20s after startup. IMAX = 10A. 2) Set fast comparator threshold (RTH). 22 From Figure 8, CTON = 3000pF. 4) Select Retry Timeout. Peak junction temperature, TJ = 150CJ Peak ambient temperature, TA = 85CA ______________________________________________________________________________________ 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection ZJA = (150C - 85C) / (5V 10A) = 1.30C/W Using t START = 1ms as the pulse duration, use Figure 17 to select a duty cycle. The duty cycle should be about 0.01 or less. This implies tRETRY = tSTART / 0.01 = 100ms. From Figure 8, CTIM = 10nF. HIGH-CURRENT PATH SENSE RESISTOR MAX4271 MAX4272 MAX4273 Layout Considerations To take full tracking advantage of the switch response time to an output fault condition, it is important to keep all traces as short as possible and to maximize the high-current trace dimensions to reduce the effect of undesirable parasitic inductance. Place the MAX4271/ MAX4272/MAX4273 close to the card's connector. Use a ground plane to minimize impedance and inductance. Minimize the current-sense resistor trace length (<10mm), and ensure accurate current sensing with Kelvin connections (Figure 18). When the output is short circuited, the voltage drop across the external MOSFET becomes large. Hence, the power dissipation across the switch increases, as does the die temperature. An efficient way to achieve good power dissipation on a surface-mount package is to lay out two copper pads directly under the MOSFET package on both sides of the board. Connect the two pads to the ground plane through vias, and use enlarged copper mounting pads on the top side of the board. Figure 18. Kelvin Connections for the Current-Sense Resistors Pin Configurations TOP VIEW RTH 1 IN 1 8 ON SENSE 2 7 STAT 6 AUXVCC 2 15 INC IN 3 14 REF SENSE 4 GATE 3 MAX4271 MAX4272 GND 4 5 16 OUTC MAX4273 13 ON GATE 5 12 STAT CTIM CEXT 6 11 CTIM CSPD LLMON 7 10 CSPD 9 GND 8 CTON SO QSOP/SO ______________________________________________________________________________________ 23 MAX4271/MAX4272/MAX4273 Calculate the MOSFET thermal resistance required for a short to ground. Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) DIM A A1 B C e E H L N E H INCHES MILLIMETERS MAX MIN 0.069 0.053 0.010 0.004 0.014 0.019 0.007 0.010 0.050 BSC 0.150 0.157 0.228 0.244 0.016 0.050 MAX MIN 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 1.27 BSC 3.80 4.00 5.80 6.20 0.40 SOICN .EPS MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection 1.27 VARIATIONS: 1 INCHES TOP VIEW DIM D D D MIN 0.189 0.337 0.386 MAX 0.197 0.344 0.394 MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.00 N MS012 8 AA 14 AB 16 AC D A B e C 0-8 A1 L FRONT VIEW SIDE VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, .150" SOIC APPROVAL DOCUMENT CONTROL NO. 21-0041 24 ______________________________________________________________________________________ REV. B 1 1 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection QSOP.EPS ______________________________________________________________________________________ 25 MAX4271/MAX4272/MAX4273 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) MAX4271/MAX4272/MAX4273 3V to 12V Current-Limiting Hot-Swap Controllers with Autoretry, DualSpeed/BiLevel Fault Protection Revision History REVISION NUMBER REVISION DATE DESCRIPTION PAGES CHANGED 0 4/00 Initial release -- 1 7/00 Removed future product designation for MAX4273 1 1a 4/01 Updated footer 1 12/07 Included Package codes in Ordering Information table, Updated Note 5 and Package Outlines 2 1, 4, 24 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.