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National Semiconductor Electronic Components Datasheet

LM20125 Datasheet

Synchronous Buck Regulator

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LM20125 pdf
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January 16, 2008
LM20125
5A, 500kHz PowerWise® Synchronous Buck Regulator
General Description
The LM20125 is a full featured 500 kHz synchronous buck
regulator capable of delivering up to 5A of continuous output
current. The current mode control loop can be compensated
to be stable with virtually any type of output capacitor. For
most cases, compensating the device only requires two ex-
ternal components, providing maximum flexibility and ease of
use. The device is optimized to work over the input voltage
range of 2.95V to 5.5V making it suited for a wide variety of
low voltage systems.
The device features internal over voltage protection (OVP)
and over current protection (OCP) circuits for increased sys-
tem reliability. A precision enable pin and integrated UVLO
allows the turn-on of the device to be tightly controlled and
sequenced. Start-up inrush currents are limited by both an
internally fixed and externally adjustable Soft-Start circuit.
Fault detection and supply sequencing is possible with the
integrated power good circuit.
The LM20125 is designed to work well in multi-rail power
supply architectures. The output voltage of the device can be
configured to track a higher voltage rail using the SS/TRK pin.
If the output of the LM20125 is pre-biased at startup it will not
sink current to pull the output low until the internal soft-start
ramp exceeds the voltage at the feedback pin.
The LM20125 is offered in a 16-pin eTSSOP package with an
exposed pad that can be soldered to the PCB, eliminating the
need for bulky heatsinks.
Features
Input voltage range 2.95V to 5.5V
Accurate current limit minimizes inductor size
97% efficiency with 500 kHz switching frequency
32 mintegrated FET switches
Starts up into pre-biased loads
Output voltage tracking
Peak current mode control
Adjustable output voltage down to 0.8V
Adjustable Soft-Start with external capacitor
Precision enable pin with hysteresis
Integrated OVP, UVLO, power good and thermal
shutdown
eTSSOP-16 exposed pad package
Applications
Simple to design, high efficiency point of load regulation
from a 5V or 3.3V bus
High Performance DSPs, FPGAs, ASICs and
microprocessors
Broadband, Networking and Optical Communications
Infrastructure
Typical Application Circuit
PowerWise® is a registered trademark of National Semiconductor Corporation.
© 2008 National Semiconductor Corporation 300302
30030201
www.national.com


National Semiconductor Electronic Components Datasheet

LM20125 Datasheet

Synchronous Buck Regulator

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LM20125 pdf
www.DataShCeeot4Un.cnomection Diagram
Ordering Information
Order Number
LM20125MH
LM20125MHE
LM20125MHX
Package Type
eTSSOP-16
30030202
Top View
eTSSOP-16 Package
NSC Package Drawing
MXA16A
Package Marking
20125MH
Supplied As
92 Units of Rail
250 Units of Tape an Reel
2500 Units of Tape and Reel
Pin Descriptions
Pin #
1
2
3
4
5,16
6,7
8,9
10,11
12
13
14
15
EP
Name
SS/TRK
FB
PGOOD
COMP
NC
PVIN
SW
PGND
EN
VCC
AVIN
AGND
Exposed Pad
Description
Soft-Start or Tracking control input. An internal 5 µA current source charges an external capacitor to
set the soft-start ramp rate. If driven by a external source less than 800 mV, this pin overrides the
internal reference that sets the output voltage. If left open, an internal 1ms soft-start ramp is activated.
Feedback input to the error amplifier from the regulated output. This pin is connected to the inverting
input of the internal transconductance error amplifier. An 800 mV reference connected to the non-
inverting input of the error amplifier sets the closed loop regulation voltage at the FB pin.
Power good output signal. Open drain output indicating the output voltage is regulating within
tolerance. A pull-up resistor of 10 kto 100 kis recommend for most applications.
External compensation pin. Connect a resistor and capacitor to this pin to compensate the device.
These pins must be connected to GND to ensure proper operation.
Input voltage to the power switches inside the device. These pins should be connected together at the
device. A low ESR capacitor should be placed near these pins to stabilize the input voltage.
Switch pin. The PWM output of the internal power switches.
Power ground pin for the internal power switches.
Precision enable input for the device. An external voltage divider can be used to set the device turn-
on threshold. If not used the EN pin should be connected to PVIN.
Internal 2.7V sub-regulator. This pin should be bypassed with a 1 µF ceramic capacitor.
Analog input supply that generates the internal bias. Must be connected to VIN through a low pass
RC filter.
Quiet analog ground for the internal bias circuitry.
Exposed metal pad on the underside of the package with a weak electrical connection to ground. It is
recommended to connect this pad to the PC board ground plane in order to improve heat dissipation.
www.national.com
2


Part Number LM20125
Description Synchronous Buck Regulator
Maker National Semiconductor
Total Page 20 Pages
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