January 16, 2008
5A, 500kHz PowerWise® Synchronous Buck Regulator
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.
■ Input voltage range 2.95V to 5.5V
■ Accurate current limit minimizes inductor size
■ 97% efficiency with 500 kHz switching frequency
■ 32 mΩ integrated 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
■ eTSSOP-16 exposed pad package
■ Simple to design, high efficiency point of load regulation
from a 5V or 3.3V bus
■ High Performance DSPs, FPGAs, ASICs and
■ Broadband, Networking and Optical Communications
Typical Application Circuit
PowerWise® is a registered trademark of National Semiconductor Corporation.
© 2008 National Semiconductor Corporation 300302