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PVIN
SW
AGND
FB
PGOOD
R
FB1
R
FB2
C
OUT
EN
C
SS
SS/TRK
AVIN
C
F
C
C1
COMP
R
C1
V
IN
LM20133
L
R
F
VCC
C
VCC
V
OUT
PGND
P
GOOD
R
PG
EN
C
C2
SYNC
SYNC
C
IN
C
BYP
User's Guide
SNVA274B–October 2007–Revised May 2013
AN-1688 LM20133 Evaluation Board
1 Introduction
The LM20133 is a full featured buck switching regulator capable of driving up to 3A of load current. This
device features a clock synchronization input that allows the switching frequency to be synchronized to an
external clock source. The flexibilty to synchronize the switching frequency from 500 kHz to 1.5 MHz
allows the size of the power stage components to be reduced while still allowing for high efficiency. The
LM20133 is capable of converting an input voltage between 2.95 V and 5.5 V down to an output voltage
as low as 0.8 V. Fault protection features include cycle-by-cycle current limit, output power good, and
output over-voltage protection. The dual function soft-start/tracking pin can be used to control the startup
response of the LM20133, and the precision enable pin can be used to easily sequence the LM20133 in
applications with sequencing requirements. The LM20133 is available in a 16-pin HTSSOP package with
an exposed pad for enhanced thermal performance.
The LM20133 evaluation board has been designed to balance overall solution size with the efficiency of
the regulator. The evaluation board measures just under 1.3” x 1.1” on a two layer PCB, with all
components placed on the top layer. The power stage and compensation components of the LM20133
evaluation board have been optimized for an input voltage of 5 V, but for testing purposes, the input can
be varied across the entire operating range. The output voltage of the evaluation board is nominally 1.2 V,
but this voltage can be easily changed by replacing one of the feedback resistors (R
FB1
or R
FB2
). The
control loop compensation of the LM20133 evaluation board has been designed to provide a stable
solution over the entire input and output voltage range with a reasonable transient response. The EN pin
must be above 1.18 V (typ) on the board to initiate switching. If the EN function is not necessary, the EN
pin should be externally tied to V
IN
.
Figure 1. Evaluation Board Schematic
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1
SNVA274B–October 2007–Revised May 2013 AN-1688 LM20133 Evaluation Board
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