LT3957
1
DESCRIPTION
Demonstration circuit 1544 is a Boost, SEPIC, Flyback
and Inverting Converter with 5A, 40V Switch featuring
the LT3957. The LT3957 can be configured as a boost,
flyback, SEPIC, and inverting converter, but the demon-
stration circuit is assembled as a boost. The input volt-
age range is 4.5V to 20V and the output voltage is 24V
with 600mA over the entire input voltage range.
The LT3957 has an internal n-channel 5A, 40V power
switch for high voltage, power, and efficiency. The dual
paddle package provides excellent heat dissipation for
the internal power switch. The LT3957 current-mode
dc/dc converter features adjustable switching frequency,
soft-start, compensation, shutdown and undervoltage
lockout with hysteresis, and a feedback pin (FBX) that
can be used in both positive and negative applications. A
SYNC input can be used to synchronize the switching at
a frequency higher than the IC is programmed.
The demonstration circuit features small 1210 case size
ceramic input and output capacitors. The internal n-
channel power switch provides efficiency as high as 95%
in typical boost applications with 14.4W output.
The LT3957 datasheet gives a complete description of
the part, operation and applications information. The
datasheet must be read in conjunction with this Quick
Start Guide for demonstration circuit 1544A. The LT3957
is assembled in a 36-lead plastic UHE package with two
thermally enhanced pads for SW and GND. Proper board
layout is essential for both proper operation and maxi-
mum thermal performance. See the datasheet section
‘Layout Considerations’.
Figure 1.
DC1544A 12VIN Efficiency
Design files for this circuit board are available. Call
the LTC factory.
L
, LT are trademarks of Linear Technology Corporation.
PARAMETER
CONDITIONS
UNITS
Minimum Input Supply Voltage
4.5
V
Maximum Input Supply Voltage
20
V
Output Voltage Programmed
V
IN
= 4.5V-20V, I
LOAD
≤
600mA
24
V
Switching Frequency
R
T
= 41.2k
300
kHz
Guaranteed Maximum Output current
V
IN
= 4.5V-20V
600
mA
Input Undervoltage Lockout (falling)
R1=200k, R2=95.3k
3.8
V
Input Turn-on Voltage (rising)
R1=200k, R2=95.3k
4.2
v
Efficiency
V
IN
= 12V, I
LOAD
=
600mA
95
%
DEMO CIRCUIT 1544
QUICK START GUIDE
LT3957
Boost, SEPIC, Flyback and Inverting Converter with 5A,
40V Switch
