VSENSE
VOUT
VCONTROL
VPOWER
CS5257A-1 2.5V @ 7A
300mF
5V
Load
124
1%
124
1%
0.1mF
5V
100mF
5V
10mF
10V
3.3V
5.0V
Adjust
Features
Package Options
CS5257A-1
7A LDO 5-Pin Adjustable Linear Regulator
CS5257A-1
Description
Applications Diagram
5 Lead TO-220
1
1. VSENSE
2. Adjust
3. VOUT
4. VCONTROL
5. VPOWER
Tab = VOUT
1
Rev. 4/5/99
This new very low dropout regula-
tor is designed to power the next
generation of advanced micropro-
cessors. To achieve very low
dropout, the internal pass transistor
is powered separately from the con-
trol circuitry. Furthermore, with the
control and power inputs tied
together, this device can be used in
single supply configuration and
still offer a better dropout voltage
than conventional PNP-NPN based
LDO regulators. In this mode the
dropout is determined by the mini-
mum control voltage.
It is supplied in five-terminal
TO-220 and D2PAK packages,
allowing for the implementation of
a remote-sense pin permitting very
accurate regulation of output volt-
age directly at the load, where it
counts, rather than at the regulator.
This remote sensing feature virtual-
ly eliminates output voltage varia-
tions due to load changes and resis-
tive voltage drops. Typical load
regulation measured at the sense
pin is 1mV for an output voltage of
2.5V with a load step of 10mA to
7A.
The very fast transient loop
response easily meets the needs of
the latest microprocessors. In addi-
tion, a small capacitor on the Adjust
pin will further improve the tran-
sient capabilities.
Internal protection circuitry pro-
vides for Òbust-proofÓ operation,
similar to three-terminal regulators.
This circuitry, which includes over-
current, short circuit, supply
sequencing and overtemperature
protection will self protect the regu-
lator under all fault conditions.
The CS5257A-1 is ideal for generat-
ing a secondary 2-2.5V low voltage
supply on a motherboard where
both 5V and 3.3V are already avail-
able.
■1.25V to 5V VOUT at 7A
■VPOWER Dropout < 0.35V @ 7A
■VCONTROL Dropout < 1.10V @
7A
■1.5% Trimmed Reference
■Fast Transient Response
■Remote Voltage Sensing
■Thermal Shutdown
■Current Limit
■Short Circuit Protection
■Drop-In Replacement for
LT1580
■Backwards Compatible with
3-pin Regulators
1
5 Lead D2PAK
Cherry Semiconductor Corporation
2000 South County Trail, East Greenwich, RI 02818
Tel: (401)885-3600 Fax: (401)885-5786
Email: info@cherry-semi.com
Web Site: www.cherry-semi.com
A Company
¨
Electrical Characteristics: 0¡C ² TA² 70¡C, 0¡C ² TJ² 150¡C, VSENSE = VOUT and VAdj = 0V; unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
CS5257A-1
2
Absolute Maximum Ratings
VPOWER Input Voltage .................................................................................................................................................................6V
VCONTROL Input Voltage ...........................................................................................................................................................13V
Operating Junction Temperature Range...........................................................................................................0¡C ² TJ² 150¡C
Storage Temperature Range................................................................................................................................-65¡C to +150¡C
Lead Temperature Soldering
Wave Solder (through hole styles only) .....................................................................................10 sec. max, 260¡C peak
Reflow (SMD styles only) ......................................................................................60 sec. max above 183¡C, 230¡C peak
ESD Damage Threshold............................................................................................................................................................2kV
Reference Voltage VCONTROL = 2.75V to 12V, VPOWER = 2.05V to 5.5V, 1.234 1.253 1.272 V
10mA ² IOUT ² 7A (-1.5%) (+1.5%)
Line Regulation VCONTROL = 2.5V to 12V, VPOWER = 1.75V to 5.5V, .02 .20 %
IOUT = 10mA
Load Regulation VCONTROL = 2.75V, VPOWER = 2.05V, .04 .20 %
(Note 3) IOUT = 10mA to 7A, with remote sense
Minimum Load Current VCONTROL = 5V, VPOWER = 3.3V, ÆVOUT = +1% 5 10 mA
(Note 1)
Control Pin Current VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 100mA 6 10 mA
(Note 2) VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 4A 30 60 mA
VCONTROL = 2.75V, VPOWER = 1.75V, IOUT = 4A 33 70 mA
VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 7A 60 180 mA
Adjust Pin Current VCONTROL = 2.75V, VPOWER = 2.05V, IOUT = 10mA 60 120 µA
Current Limit VCONTROL = 2.75V, VPOWER = 2.05V, ÆVOUT = -1.5% 7.1 10.0 A
Short Circuit Current VCONTROL = 2.75V, VPOWER = 2.05V, VOUT = 0V 5.0 9.0 A
Ripple Rejection VCONTROL = VPOWER = 3.25V, 60 80 dB
(Note 3) VRIPPLE = 1VP-P @ 120Hz, IOUT = 4A, CADJ = 0.1µF
Thermal Regulation 30ms Pulse, TA = 25¡C 0.002 %/W
VCONTROL Dropout Voltage VPOWER = 2.05V, IOUT = 100mA 1.00 1.15 V
(Minimum VCONTROL-VOUT)V
POWER = 2.05V, IOUT = 1A 1.00 1.15 V
(Note 4) VPOWER = 2.05V, IOUT = 2.75A 1.00 1.15 V
VPOWER = 2.05V, IOUT = 4A 1.00 1.15 V
VPOWER = 2.05V, IOUT = 7A 1.10 1.25 V
VPOWER Dropout Voltage VCONTROL = 2.75V, IOUT = 100mA .10 .15 V
(Minimum VPOWER-VOUT)V
CONTROL = 2.75V, IOUT = 1A .15 .20 V
(Note 4) VCONTROL = 2.75V, IOUT = 2.75A .20 .30 V
VCONTROL = 2.75V, IOUT = 4A .26 .40 V
VCONTROL = 2.75V, IOUT = 7A .35 .65 V
RMS Output Noise Freq = 10Hz to 10kHz, TA = 25¡C 0.003 %VOUT
Temperature Stability 0.5 %
Thermal Shutdown (Note 5) 150 180 210 ¡C
Thermal Shutdown Hysteresis 25 ¡C
VCONTROL Supply Only VCONTROL = 13V, VPOWER not connected, 50 mA
Output Current VADJUST = VOUT = VSENSE = 0V
CS5257A-1
Package Pin Description
PACKAGE PIN # PIN SYMBOL FUNCTION
3
Block Diagram
VCONTROL
BIAS
and
TSD
VREF EA IA VOUT
VSENSE
Adjust
-
+-
+
VPOWER
Electrical Characteristics: 0¡C ² TA² 70¡C, 0¡C ² TJ² 150¡C, VSENSE = VOUT and VAdj = 0V unless otherwise specified.
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VPOWER Supply Only VPOWER = 6V, VCONTROL not connected, 0.1 1 mA
Output Current VADJUST = VOUT = VSENSE = 0V
Note 1: The minimum load current is the minimum current required to maintain regulation. Normally the current in the resistor divider used to set
the output voltage is selected to meet the minimum load current requirement.
Note 2: The VCONTROL pin current is the drive current required for the output transistor. This current will track output current with roughly a 1:100
ratio. The minimum value is equal to the quiescent current of the device.
Note 3: This parameter is guaranteed by design and is not 100% production tested.
Note 4: Dropout is defined as either the minimum control voltage, (VCONTROL) or minimum power voltage (VPOWER) to output voltage differential
required to maintain 1.5% regulation at a particular load current.
Note 5: This parameter is guaranteed by design, but not parametrically tested in production. However, a 100% thermal shutdown functional test is
performed on each part.
5L TO-220
1V
SENSE This Kelvin sense pin allows for remote sensing of the output voltage at the
load for improved regulation. It is internally connected to the positive input
of the voltage sensing error amplifier.
2 Adjust This pin is connected to the low side of the internally trimmed 1.5% bandgap
reference voltage and carries a bias current of about 50µA. A resistor divider
from Adj to VOUT and from Adj to ground sets the output voltage. Also,
transient response can be improved by adding a small bypass capacitor from
this pin to ground.
3V
OUT This pin is connected to the emitter of the power pass transistor and pro-
vides a regulated voltage capable of sourcing 7A of current.
4V
CONTROL This is the supply voltage for the regulator control circuitry. For the device
to regulate, this voltage should be between 1V and 1.25V (depending on the
output current) greater than the output voltage. The control pin current will
be about 1% of the output current.
5V
POWER This is the power input voltage. The pin is physically connected to the collec-
tor of the power pass transistor. For the device to regulate, this voltage
should be between 0.1V and 0.65V greater than the output voltage, depend-
ing on output current. The output load current of 7A is supplied through
this pin.
CS5257A-1
4
Typical Performance Characteristics
0 10 20 30 40 50 60 70 80 90 100 110120130
-0.150
-0.125
-0.100
-0.075
-0.050
-0.025
-0.000
0.025
0.050
0.075
0.100
TJ (°C)
Output Voltage Deviation (%)
I0=10mA
VCONTROL=2.75V,
VPOWER=2.05V
Reference Voltage vs Temperature
50
0
-50
-100
7
0
02 5
0
Time (ms)
Output Voltage Deviation (mV)Current (A)
100
134
COUT=330mF
CPOWER=110mF
CCONTROL=10mF
CADJUST=0.1mF
VCONTROL=5V
VPOWER=3.3V
VOUT=2.5V
Transient Response
0.0 0.5
0.0
15.0
Output Current (A)
VPOWER-VOUT (V)
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
14.0
13.0
12.0
6.0
5.0
4.0
3.0
2.0
1.0
11.0
10.0
7.0
8.0
9.0
VCONTROL=2.75V
Short Circuit Current vs VPOWER-VOUT
0.0
83.0
Adjust Pin Current (mA)
Temperature (C)
40.0 60.0 80.0 100.0
81.0
79.0
77.0
75.0
73.0
71.0
69.0
67.0
65.0
20.0 120.0 160.0140.0
Adjust Pin Current vs Temperature
1.0 3.0 4.0 5.0 6.0 7.0
800.000
Minimum Load Current (mA)
VCONTROL-VOUT (V)
9.0 10.0 11.02.0 8.0
850.000
900.000
950.000
1000.000
1050.000
1100.000
1150.000
1200.000
VPOWER =3.3V
D VOUT=+1%
Minimum Load Current vs VCONTROL-VOUT
3.002.000.00
0.000
0.060
0.070
0.080
0.090
0.100
Output Current (A)
Output Voltage Deviation (%)
1.00 4.00 6.005.00 7.00
0.010
0.020
0.050
0.040
0.030
VPOWER=2.05V
VCONTROL=2.75V
Load Regulation vs Output Current
CS5257A-1
5
Typical Performance Characteristics: continued
10.0
101
Frequency (Hz)
Ripple Rejection (dB)
20.0
30.0
40.00
60.0
70.0
80.0
90.0
102103104106
105
50.0
VIN-VOUT=2V
IOUT=4A
VRIPPLE=1VP-P
COUT=22mF
CADJ=0.1mF
Ripple Rejection vs Frequency
1.0 3.0 4.0 5.0 6.0 7.0
70.00
Adjust Pin Current (mA)
VCONTROL-VOUT (V)
9.0
71.00
72.00
73.00
74.00
75.00
10.0 11.02.0 8.0
VPOWER =2.05V
IL=10mA
Adjust Pin Current vs VCONTROL-VOUT
0.00
0.000
1.000
VPOWER Dropout Voltage (V)
Output Current (A)
1.00 2.00 3.00 4.00 5.00 6.00 7.00
0.900
0.800
0.700
0.600
0.500
0.400
0.300
0.200
0.100
VCONTROL =2.75V
VPOWER Dropout Voltage vs IOUT
0.50
70.00
Adjust Pin Current (mA)
VPOWER-VOUT (V)
2.50
71.00
72.00
73.00
74.00
75.00
3.50 4.501.50
VCONTROL=2.75V
IL=10mA
3.002.000.00
0.00
0.250
0.500
0.750
1.000
1.250
Output Current (A)
VCONTROL Drop Out Voltage (V)
VPOWER=2.05V
1.00 4.00 6.005.00 7.00
VCONTROL Dropout Voltage vs IOUT
Adjust Pin Current vs VPOWER - VOUT
0.50 1.50 2.50
915.500
Minimum Load Current (mA)
VPOWER-VOUT (V) 3.50 4.50
915.600
915.700
915.800
915.900
916.000
916.100
916.200
916.400
VCONTROL =5V
D VOUT=+1%
915.400
916.300
Minimum Load Current vs VPOWER-VOUT
CS5257A-1
6
Application Notes
Typical Performance Characteristics: continued
74.00
76.00
77.00
0.00 1.00 5.00 7.00
Output Current (A)
Adjust Pin Current (mA)
75.00
73.00
72.00
6.002.00 3.00 4.00 8.00
VPOWER=2.05
VCONTROL=2.75V
Adjust Pin Current vs Output Current
The CS5257A-1 linear regulator provides adjustable volt-
ages from 1.25V to 5V at currents up to 7A. The regulator
is protected against short circuits, and includes a thermal
shutdown circuit with hysteresis. The output, which is cur-
rent limited, consists of a PNP-NPN transistor pair and
requires an output capacitor for stability. A detailed pro-
cedure for selecting this capacitor is included in the
Stability Considerations section.
VPOWER Function
The CS5257A-1 utilizes a two supply approach to maxi-
mize efficiency. The collector of the power device is
brought out to the VPOWER pin to minimize internal power
dissipation under high current loads. VCONTROL provides
power for the control circuitry and the drive for the output
NPN transistor. VCONTROL should be at least 1V greater
than the output voltage. Special care has been taken to
ensure that there are no supply sequencing problems. The
output voltage will not turn on until both supplies are
operating. If the control voltage comes up first, the output
current will be typically limited to about 3mA until the
power input voltage comes up. If the power input voltage
comes up first the output will not turn on at all until the
control voltage comes up. The output can never come up
unregulated.
The CS5257A-1 can also be used as a single supply device
with the control and power inputs tied together. In this
mode, the dropout will be determined by the minimum
control voltage.
Output Voltage Sensing
The CS5257A-1 five terminal linear regulator includes a
dedicated VSENSE function. This allows for true Kelvin
sensing of the output voltage. This feature can virtually
eliminate errors in the output voltage due to load regula-
tion. Regulation will be optimized at the point where the
sense pin is tied to the output.
Adjustable Operation
This LDO adjustable regulator has an output voltage range
of 1.25V to 5V. An external resistor divider sets the output
voltage as shown in Figure 1. The regulatorÕs voltage sens-
ing error amplifier maintains a fixed 1.253V reference
between the output pin and the adjust pin.
A resistor divider network R1and R2causes a fixed current
to flow to ground. This current creates a voltage across R2
that adds to the 1.253V across R1and sets the overall out-
put voltage. The adjust pin current (typically 50µA) also
flows through R2and adds a small error that should be
taken into account if precise adjustment of VOUT is neces-
sary. The output voltage is set according to the formula:
VOUT = 1.253V ´+ R2 ´ IADJ
The term IADJ ´R2represents the error added by the adjust
pin current. R1is chosen so that the minimum load current
is a least 10mA. R1and R2should be of the same composi-
tion for best tracking over temperature. The divider resis-
tors should be placed physically as close to the load as pos-
sible.
Figure 1: An external resistor divider sets the value of VOUT. The 1.253V
reference voltage drops across R1.
VSENSE
VOUT
VCONTROL
VPOWER
CS5257A-1
R1
Adjust
R2
R1+R2
R1
Design GuidelinesTheory of Operation
CS5257A-1
7
Application Notes: continued
While not required, a bypass capacitor connected between
the adjust pin and ground will improve transient response
and ripple rejection. A 0.1µF tantalum capacitor is recom-
mended for Òfirst cutÓ design. Value and type may be var-
ied to optimize performance vs. price.
Other Adjustable Operation Considerations
The CS5257A-1 linear regulator has an absolute maximum
specification of 6V for the voltage difference between VIN
and VOUT. However, the IC may be used to regulate volt-
ages in excess of 6V. The two main considerations in such a
design are the sequencing of power supplies and short cir-
cuit capability.
Power supply sequencing should be such that the VCON-
TROL supply is brought up coincidentally with or before the
VPOWER supply. This allows the IC to begin charging the
output capacitor as soon as the VPOWER to VOUT differential
is large enough that the pass transistor conducts. As VPOW-
ER increases, the pass transistor will remain in dropout, and
current is passed to the load until VOUT is in regulation.
Further increase in the supply voltage brings the pass tran-
sistor out of dropout. In this manner, any output voltage
less than 13V may be regulated, provided the VPOWER to
VOUT differential is less than 6V. In the case where VCON-
TROL and VPOWER are shorted, there is no theoretical limit
to the regulated voltage as long as the VPOWER to VOUT dif-
ferential of 6V is not exceeded.
There is a possibility of damaging the IC when VPOWER-VIN
is greater than 6V if a short circuit occurs. Short circuit con-
ditions will result in the immediate operation of the pass
transistor outside of its safe operating area. Over-voltage
stresses will then cause destruction of the pass transistor
before overcurrent or thermal shutdown circuitry can
become active. Additional circuitry may be required to
clamp the VPOWER to VOUT differential to less than 6V if fail
safe operation is required. One possible clamp circuit is
illustrated in Figure 2; however, the design of clamp cir-
cuitry must be done on an application by application basis.
Care must be taken to ensure the clamp actually protects
the design. Components used in the clamp design must be
able to withstand the short circuit condition indefinitely
while protecting the IC.
Figure 2: Example clamp circuitry for VPOWER -VOUT > 6V.
Stability Considerations
The output compensation capacitor helps determine three
main characteristics of a linear regulator: start-up delay,
load transient response, and loop stability.
The capacitor value and type is based on cost, availability,
size and temperature constraints. A tantalum or aluminum
electrolytic capacitor is best, since a film or ceramic capaci-
tor with almost zero ESR can cause instability. The alu-
minum electrolytic capacitor is the least expensive solution.
However, when the circuit operates at low temperatures,
both the value and ESR of the capacitor will vary consider-
ably. The capacitor manufacturer's data sheet provides this
information.
A 300µF tantalum capacitor will work for most applica-
tions, but with high current regulators such as the
CS5257A-1 the transient response and stability improve
with higher values of capacitor. The majority of applica-
tions for this regulator involve large changes in load cur-
rent so the output capacitor must supply the instantaneous
load current. The ESR of the output capacitor causes an
immediate drop in output voltage given by:
ÆV = ÆI ´ ESR.
For microprocessor applications it is customary to use an
output capacitor network consisting of several tantalum
and ceramic capacitors in parallel. This reduces the overall
ESR and reduces the instantaneous output voltage drop
under transient load conditions. The output capacitor net-
work should be as close to the load as possible for the best
results.
Protection Diodes
When large external capacitors are used with a linear
regulator it is sometimes necessary to add protection
diodes. If the input voltage of the regulator gets shorted,
the output capacitor will discharge into the output of the
regulator. The discharge current depends on the value of
the capacitor, the output voltage, and the rate at which
VCONTROL drops. In the CS5257A-1 regulator, the discharge
path is through a large junction and protection diodes are
not usually needed. If the regulator is used with large val-
ues of output capacitance and the input voltage is instanta-
neously shorted to ground, damage can occur. In this case,
a diode connected as shown in Figure 3 is recommended.
Use of the diode has the added benefit of bleeding VOUT to
ground if VCONTROL is shorted. This prevents an unregulat-
ed output from causing system damage.
Figure 3: Diode protection against VCONTROL short circuit conditions.
VSENSE
VOUT
VCONTROL
VPOWER
CS5257A-1
Adjust
External Supply
VControl
VPower
VAdjust
VOUT
VSENSE
8
CS5257A-1
Application Notes: continued
A rule of thumb useful in determining if a protection diode
is required is to solve for current
I= C ´ V , where
T
I is the current flow out of the load capacitance
when VCONTROL is shorted,
C is the value of load capacitance
V is the output voltage, and
T is the time duration required for VCONTROL
to transition from high to being shorted.
If the calculated current is greater than or equal to the typi-
cal short circuit current value provided in the specifica-
tions, serious thought should be given to the use of a pro-
tection diode.
Current Limit
The internal current limit circuit limits the output current
under excessive load conditions.
Short Circuit Protection
The device includes short circuit protection circuitry that
clamps the output current at approximately two amperes
less than its current limit value. This provides for a current
foldback function, which reduces power dissipation under
a direct shorted load.
Thermal Shutdown
The thermal shutdown circuitry is guaranteed by design to
activate above a die junction temperature of approximately
150¡C and to shut down the regulator output. This circuit-
ry has 25¡C of typical hysteresis, thereby allowing the reg-
ulator to recover from a thermal fault automatically.
Calculating Power Dissipation
and Heat Sink Requirements
High power regulators such as the CS5257A-1 usually
operate at high junction temperatures. Therefore, it is
important to calculate the power dissipation and junction
temperatures accurately to ensure that an adequate heat
sink is used. Since the package tab is connected to Vout on
the CS5257A-1, electrical isolation may be required for
some applications. Also, as with all high power packages,
thermal compound in necessary to ensure proper heat
flow. For added safety, this high current LDO includes an
internal thermal shutdown circuit
The thermal characteristics of an IC depend on the follow-
ing four factors: junction temperature, ambient tempera-
ture, die power dissipation, and the thermal resistance
from the die junction to ambient air. The maximum junc-
tion temperature can be determined by:
TJ(max) = TA(max) + PD(max) ´RQJA
The maximum ambient temperature and the power dissi-
pation are determined by the design while the maximum
junction temperature and the thermal resistance depend on
the manufacturer and the package type. The maximum
power dissipation for a regulator is:
PD(max) = (VIN(max) -VOUT(min))IOUT(max) + VIN(max) ´ IIN(max)
A heat sink effectively increases the surface area of the
package to improve the flow of heat away from the IC and
into the surrounding air. Each material in the heat flow
path between the IC and the outside environment has a
thermal resistance which is measured in degrees per watt.
Like series electrical resistances, these thermal resistances
are summed to determine the total thermal resistance
between the die junction and the surrounding air, RQJA.
This total thermal resistance is comprised of three compo-
nents. These resistive terms are measured from junction to
case (RQJC), case to heat sink (RQCS), and heat sink to ambi-
ent air (RQSA). The equation is:
RQJA = RQJC + RQCS + RQSA
The value for RQJC is 1.4ûC/watt for the CS5257A-1 in both
the TO-220 and D2PAK packages. For a high current regu-
lator such as the CS5257A-1 the majority of heat is generat-
ed in the power transistor section. The value for RQSA
depends on the heat sink type, while the RQCS depends on
factors such as package type, heat sink interface (is an
insulator and thermal grease used?), and the contact area
between the heat sink and the package. Once these calcula-
tions are complete, the maximum permissible value of
RQJA can be calculated and the proper heat sink selected.
For further discussion on heat sink selection, see our
Cherry application note ÒThermal Management for Linear
Regulators.Ó
9
Rev. 4/5/99
Thermal Data 5L 5L
TO-220 D2PAK
RQJC typ 1.4 1.4 ûC/W
RQJA typ 50 10-50* ûC/W
*Depending on thermal properties of substrate. RqJA = RqJC + RqCA
Package Specification
PACKAGE THERMAL DATA
Ordering Information
Part Number Description
CS5257A-1GT5 5L TO-220 Straight
CS5257A-1GDP5 5L D2PAK
CS5257A-1GDPR5 5L D2PAK (tape & reel)
© 1999 Cherry Semiconductor Corporation
CS5257A-1
Cherry Semiconductor Corporation reserves the right to
make changes to the specifications without notice. Please
contact Cherry Semiconductor Corporation for the latest
available information.
PACKAGE DIMENSIONS IN mm (INCHES)
5 Lead D2PAK (DP)
1.70 (.067) REF
0.10 (.004)
0.00 (.000)
10.31 (.406)
10.05 (.396)
0.91 (.036)
0.66 (.026)
1.40 (.055)
1.14 (.045)
4.57 (.180)
4.31 (.170)
1.68 (.066)
1.40 (.055)
2.74(.108)
2.49(.098)
.254 (.010) REF
2.79 (.110)
2.29 (.090)
15.75 (.620)
14.73 (.580)
8.53 (.336)
8.28 (.326)
5 Lead TO-220 (T) Straight