Linear Technology DC1544 Quick Start Manual

Boost, SEPIC, Flyback and Inverting Converter with 5A,
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
PARAMETER
Minimum Input Supply Voltage
Maximum Input Supply Voltage
Output Voltage Programmed
Switching Frequency
Guaranteed Maximum Output current
Input Undervoltage Lockout (falling)
Input Turn-on Voltage (rising)
Efficiency
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'.
Design files for this circuit board are available. Call
the LTC factory.
L , LT are trademarks of Linear Technology Corporation.
CONDITIONS
V = 4.5V-20V, I ≤ 600mA
IN LOAD
R = 41.2k
T
V = 4.5V-20V
IN
R1=200k, R2=95.3k
R1=200k, R2=95.3k
V = 12V, I = 600mA
IN LOAD
DEMO CIRCUIT 1544
QUICK START GUIDE
40V Switch
Figure 1. DC1544A 12VIN Efficiency
4.5
20
24
300
600
3.8
4.2
95
LT3957
LT3957
UNITS
V
V
V
kHz
mA
V
v
%
1