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dc607afa
DEMO MANUAL DC607A
Description
LTC3722, LTC4440, LTC3901,
and LT1431
Isolated Full Bridge Converter
Demonstration circuit 607A is an isolated full bridge
converter featuring the
LTC3722
,
LTC4440
,
LTC3901
,
and
LT1431
. This circuit was designed to demonstrate the
phase-shifted full bridge power supply to generate 12V
at 35A from a typical telecom input voltage range of 36V
to 72V. Isolation voltage is 1500VDC. Fixed zero-voltage
transition timing was chosen because of the relatively fast
L
, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog
Devices, Inc. All other trademarks are the property of their respective owners.
performance summary
operating principles
bridge leg transition times with a 48V input. The DC607A
PCB layout includes options to implement adaptive timing.
Design files for this circuit board are available at
http://www.linear.com/demo/DC607A
Specifications are at T
A
= 25°C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Input Supply Range
36
72
V
V
OUT
Output Voltage
12.0
V
I
OUT
Output Current Range
V
IN
= 48V, 200LFM
0
35
A
f
SW
Switching (Clock) Frequency
200
kHz
V
OUT(P-P)
Output Ripple
V
IN
= 48V, I
OUT
= 35A (20MHz BW)
140
mV
P-P
I
REG
Output Regulation
Line and Load (36V to 72V, 0A to 35A)
±0.08
%
P
OUT
/P
IN
Efficiency
V
IN
= 48V, I
OUT
= 35A
>93.9
%
P
OUT
/P
IN
Efficiency
V
IN
= 48V, I
OUT
= 25A
>94.6
%
Isolation
Basic
1500
VDC
Approximate Size
Component Area × Top Component Height
4.3 × 2.9 × 0.4
Inches
The LTC3722 synchronous dual mode phase modulated
full bridge controller is used on the primary and works
together with the LTC3901 secondary side synchronous
driver to provide a synchronous rectified output. When an
input voltage is applied, the LTC3722 begins a controlled
soft-start of the output voltage. As this voltage begins
to rise, the LT1431 programmable reference is quickly
powered up via the output voltage. The LT1431 provides
feedback via opto-coupler ISO1 to set the output voltage
at 12V. The LTC4440 high voltage gate driver is used to
level shift the high side primary MOSFETs gate signals.
The LTC3722 provides precise control of gate signals to
primary MOSFETs and secondary MOSFETs via T3 and
U1 (LTC3901). The LTC3901 includes a timer and current
sense to limit reverse inductor current.
For large values of input inductance, a 100V, 47µF electro-
lytic capacitor can be added across the input terminals to
damp the input filter and provide adequate stability. See
Linear Technology Application Note 19 for a discussion
on input filter stability analysis. A recommended part is
the SUNCON 100ME47AX.
