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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
LM20123
L
R
F
VCC
C
VCC
V
OUT
PGND
P
GOOD
R
PG
EN
C
C2
C
IN
C
BYP
User's Guide
SNVA272B–October 2007–Revised May 2013
AN-1686 LM20123 Evaluation Board
1 Introduction
The LM20123 is a full featured buck switching regulator capable of driving up to 3A of load current. The
nominal 1.5 MHz switching frequency of the LM20123 reduces the size of the power stage components
while still allowing for highly efficient operation. The LM20123 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 LM20123, and the precision enable
pin can be used to easily sequence the LM20123 in applications with sequencing requirements. The
LM20123 is available in an HTSSOP-16 package with an exposed pad for enhanced thermal performance.
The LM20123 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 LM20123
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 LM20123 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
SNVA272B–October 2007–Revised May 2013 AN-1686 LM20123 Evaluation Board
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