PAM2320
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3A LOW NOISE STEP-DOWN DC-DC CO NVERTE R
Description
The PAM2320 is a 3A step-down DC-DC converter. At heavy load,
the constant-frequency PWM control performs excellent stability and
transient response. No external compensation components are
required.
The PAM2320 supports a range of input voltages from 2.7V to 5.5V,
allowing the use of a single Li+/Li-polymer cell, multiple Alkaline/NiMH
cell, and other standard power sources. The output voltage is
adjustable from 0.6V to the input voltage. The PAM2320 employs
internal power switch and synchronous rectifier to minimize external
part count and realize high efficiency. During shutdown, the input is
disconnected from the output and the shutdown current is less than
1µA. Other key features include over-temperature and short circuit
protection, and under-voltage lockout to prevent deep battery
discharge.
The PAM2320 delivers 3A maximum output current while consuming
only 42µA of no-load quiescent current. Ultra-low RDS(ON) integrated
MOSFETs and 100% duty cycle operation make the PAM2320 an
ideal choice for high output voltage, high current applications which
require a low dropout threshold.
The PAM2320 is available in PSOP8 package.
Features
• Output Current: Up to 3A
• Output Voltage: 0.6V to VIN
• Input Voltage: 2.7 to 5.5V
• Efficiency up to 95%
• 42µA (typ) No Load Quiescent Current
• Shutdown Current: <1µA
• 100% Duty Cycle Operation
• 1.5MHz Switching Frequency
• Internal Soft Start
• No external Compensation Required
• Current Limit Protection
• Thermal Shutdown
• PSOP-8 Package
Pin Assignments
Applications
• 5V or 3.3V Point of Load Conversion
• Telecom/Networking Equipment
• Set Top Boxes
• Storage Equipment
• Video Cards
• DDR Power Supply
PAM2320
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Typical Applications Circuit
V2R
1R
16.0O ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛+×=
Pin Descriptions
Pin
Number PSOP-8
Pin Name Function
1 NC
Not Connected.
2 VIN
Bias supply. Chip main power supply pin.
3 SW
The drains of the internal main and synchronous power MOSFET.
4 GND
Ground
5 FB
Feedback voltage to internal error amplifier, the threshold voltage is 0.6V.
6 NC
Not Connected.
7 EN
Enable control input. Force this pin voltage above 1.5V, enables the chip, and below 0.3V shuts down
the device.
8 NC
Not Connected.
Functional Block Diagram
PAM2320
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Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.)
These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may
affect device reliability. All voltages are with respect to ground.
Parameter Rating Unit
Input Voltage VIN 6 V
SW Pin Voltage -0.3 to (VIN +0.3) V
FB Pin Voltage -0.3 to (VIN +0.3) V
EN Pin Voltage -0.3 to +6.0 V
Maximum Junction Temperature 150 °C
Storage Temperature Range -65 to +150 °C
Soldering Temperature 300, 5sec °C
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Parameter Rating Unit
Supply Voltage 2.7 to 5.5 V
Junction Temperature Range -40 to +125 °C
Ambient Temperature Range -40 to +85
Thermal Information
Parameter Symbol Package Max Unit
Thermal Resistance (Junction to Ambient) θJA PSOP-8 90
°C/W
Thermal Resistance (Junction to Case) θJC PSOP-8 14
Internal Power Dissipation (@TA= 25°C) PD PSOP-8 1100 mW
PAM2320
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Electrical Characteristics (@TA = +25°C, VIN = 3.6V, VO = 1.8V, CIN = 22µF, CO = 22µF, L = 2.2µH, unless otherwise specified.)
Parameter Symbol Test Conditions Min Typ Max Units
Input Voltage Range VIN 2.7 5.5 V
Output Voltage Range VO 0.6 VIN V
UVLO Threshold VUVLO
VIN Rising 2.4 2.5 V
Hysteresis 240 mV
VIN Falling 1.8 V
Regulated Output Voltage Accuracy VO I
O = 0 to 3A -3 +2 %
Regulated Feedback Voltage VFB 0.591 0.600 0.609 V
FB Leakage Current IFB V
O =1V 0.2 µA
Output Voltage Line Regulation LNR VIN = 2.5V to 5V 0.2 %/V
Output Voltage Load Regulation LDR IO = 0A to 3A 0.5 %/A
Quiescent Current IQ No Load 42 90 µA
Shutdown Current ISD V
EN = 0V 1 µA
Current Limit ILIM 4 A
Oscillator Frequency fOSC 1.2 1.5 1.8 MHz
Drain-Source On-State Resisitance RDS(ON) High Side 0.85 mΩ
Low Side 60 mΩ
High Efficiency η 95 95 %
Analog Soft-Start Time tS From enable to output regulation 0.5 3 ms
EN Threshold High VEH 1.5 V
EN Threshold Low VEL 0.3 V
EN Leakage Current IEN VIN = VEN = 0V -1.0 +1.0 µA
Over Temperature Protection OTP 150 °C
OTP Hysteresis OTH 30 °C
PAM2320
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Typical Performance Characteristics (@TA = +25°C, CIN = 33µF, CO = 22µF, unless otherwise specified.)
PAM2320
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Typical Performance Characteristics (cont.) (@TA = +25°C, CIN = 33µF, CO = 22µF, unless otherwise specified.)
PAM2320
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Typical Performance Characteristics (cont.) (@TA = +25°C, CIN = 33µF, CO = 22µF, unless otherwise specified.)
PAM2320
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Application Information
The basic PAM2320 application circuit is shown in Page 2. External component selection is determined by the load requirement, selecting L first
and then CIN and COUT.
Inductor Selection
For most applications, the value of the inductor will fall in the range of 1μH to 3.3μH. Its value is chosen based on the desired ripple current and
efficiency. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher VIN or VOUT also increases
the ripple current as shown in equation 3A reasonable starting point for setting ripple current is ΔIL = 1.2A (40% of 3A).
()( )
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−=
ΔV
V
1
V
Lf
1
I
IN
OUT
OUTL Equation (1)
The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation.
Thus, a 4.2A rated inductor should be enough for most applications (3A + 1.2A). For better efficiency, choose a low DC-resistance inductor.
VO 1.2V 1.5V 1.8V 2.5V 3.3V
L 1µH 1.5µH 2.2µH 2.2µH 3.3µH
CIN and COUT Selection
In continuous mode, the source current of the top MOSFET is a square wave of duty cycle VOUT/VIN. To prevent large voltage transients, a low
ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given by:
()
[]
V
VVV
II
required
C
IN
2/1
OUTINOUT
OMAXRMS
IN
−
≅
This formula has a maximum at VIN = 2VOUT, where IRMS =IOUT /2. This simple worst-case condition is commonly used for design because even
significant deviations do not offer much relief. Note that the capacitor manufacturer's ripple current ratings are often based on 2000 hours of life.
This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Consult the
manufacturer if there is any question.
The selection of COUT is driven by the required effective series resistance (ESR).
Typically, once the ESR requirement for COUT has been met, the RMS current rating generally far exceeds the IRIPPLE (P-P) requirement. The
output ripple ΔVOUT is determined by:
()
C
f8/1ESR
IV OUT
LOUT +
Δ
≈
Δ
Where f = operating frequency, COUT = output capacitance and ΔIL = ripple current in the inductor. For a fixed output voltage, the output ripple is
highest at maximum input voltage since ΔIL increases with input voltage.
Using Ceramic Input and Output Capacitors
Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and
low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size.
When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formul ations. These dielectrics have the best
temperature and voltage characteristics of all the ceramics for a given value and size.
Thermal Consideration
Thermal protection limits power dissipation in the PAM2320. When the junction temperature exceeds +150°C, the OTP (Over Temperature
Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature
drops below +120°C.
For continuous operation, the junction temperature should be maintained below +125°C. The power dissipation is defined as:
()
()
VIIF
t
V
RVVRV
IP INQOS
SW
IN
L)ON(DSOINH)ON(DSO
2
OD ++
−+
=
IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses.
PAM2320
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Application Information (cont.)
For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:
VIRIP INQH)ON(DS
2
OD +=
Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input
voltage range. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding airflow
and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula:
θ
−
=
JA
A)MAX(J
D
TT
P
Where TJ(max) is the maximum allowable junction temperature +125°C. TA is the ambient temperature and θJA is the thermal resistance from the
junction to the ambient. Based on the standard JEDEC for a two layers thermal test board, the thermal resistance θJA of SOP-8(EP) 90°C/W
respectively. The maximum power dissipation at TA = +25°C can be calculated by following formula:
P
D = (125°C - 25°C) /90°C/W = 1.11W (SOP-8)
Setting the Output Voltage
The internal reference is 0.6V (Typical). The output voltage is calculated as below:
The output voltage is given by Table 1.
⎟
⎠
⎞
⎜
⎝
⎛+= 2R
1R
1x6.0
VO
Table 1: Resistor selection for output voltage setting.
VO R1 R2
1.2V 150k 150k
1.5V 225k 150k
1.8V 300k 150k
2.5V 475k 150k
3.3V 680k 150k
100% Duty Cycle Operation
As the input voltage approaches the output voltage, the converter turns the P-Channel transistor continuously on. In this mode the output voltage
is equal to the input voltage minus the voltage drop across the P-Channel transistor:
()
RRIVV LDSONLOADINOUT +−=
where RDS(ON) = P-Channel switch ON resistance, ILOAD = Output Current, RL = Inductor DC Resistance
UVLO and Soft-Start
The reference and the circuit remain reset until the VIN crosses its UVLO threshold.
The PAM2320 has an internal soft-start circuit that limits the in-rush current during start-up. This prevents possible voltage drops of the input
voltage and eliminates the output voltage overshoot. The soft-start make the output voltage rise up smoothly.
Short Circuit Protection
The switch peak current is limited cycle-by-cycle to a typical value of 4A. In the event of an output voltage short circuit, the device operates with
a frequency of 500kHz and minimum duty cycle, therefore the average input current is more smaller than current limit.
Thermal Shutdown
When the die temperature exceeds +150°C, a reset occurs and the reset remains until the temperature decrease to +120°C, at which time the
circuit can be restarted.
PAM2320
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Ordering Information
Part Number Output Voltage Package Type Standard Package
PAM2320BECADJR ADJ PSOP-8 25000 Units/Tape & Reel
Marking Information
PAM2320
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Package Outline Dimensions (All dimensions in mm.)
PSOP-8
PAM2320
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