Datasheet
LT1952/LT1952-1
23
19521fe
36V to 72V Input, 3.3V 40A Converter
An LT1952-based synchronous forward converter provides
the ideal solution for power supplies requiring high efficiency
at low output voltages and high load currents. The 3.3V 40A
solution in Figure 18 achieves peak efficiencies of 92.5%
(Figure 17) by minimizing power loss due to rectification
at the output. Synchronous rectifier control output SOUT,
with programmable delay, optimizes timing control for a
secondary side synchronous MOSFET controller (LTC3900)
which results in high efficiency synchronous rectification.
The LT1952/LT1952-1 use a precision current limit threshold
at the OC pin combined with a soft-start hiccup mode to
provide low stress output short-circuit protection. The
maximum output current will vary only 10% over the full V
IN
range. During short-circuit the average power dissipation
of the circuit will be lower than 15% of maximum rated
power thanks to a soft-start controlled hiccup mode.
APPLICATIONS INFORMATION
This allows a significant reduction in power component
sizing using the LT1952-based converter.
OUTPUT CURRENT (A)
0 10
EFFICIENCY (%)
50
1952 F17
20
30
40
94
93
92
91
90
89
88
87
86
V
IN
= 48V
V
OUT
= 3.3V
f
OSC
= 300kHz
Figure 17. LT1952-Based Synchronous Forward Converter
Efficiency vs Load Current (For Circuit in Figure 18)
Figure 18. 36V to 72V, 3.3V at 40A Synchronous Forward Converter
•
••
••
LTC3900
8V
BIAS
V
U1
V
U1
220pF
BAT760
8V
BIAS
3
FG
5
CG
+V
IN
36V TO 72V
PA0912.002
BAS516
BCX55
V
OUT
3.3V, 40A
10k
10k
10k
1nF
8V
BIAS
1mF
15k
560Ω
C
OUT
100µF
3x
0.1µF
2.2mF
1nF
12V
Q2
PH3230
2x
Q3
PH3230
2x
+
–
18V
270Ω
PS2801
T2
Q4470-B
2.2nF
V
U1
18k
249k 80.6k
1µF
0.1µF
10k
10k
82k
47k
4
3
5
4
8
2
1
LT1009
LT1797
1952 F18
L1
SD_V
SEC
OUT
LT1952
7 14
R
OSC
V
IN
3 15
BLANK GND
9 8
SS_MAXDC PGND
5 13
DELAY
12
V
R
= 2.5V OC
6 11
COMP I
SENSE
1 10
FB = 1.23V SOUT
2 16
•
Si7846
1
GND
6
CS
+
2
V
CC
4
CS
–
7
SYNC
8
TIMER
370k
10mΩ
1µF
470Ω
39k
13.2k
115k
27k
0.22µF
0.1µF
10k59k
33k
2.2k
22k
L1: PA0713, PULSE ENGINEERING
ALL CAPACITORS X7R, CERAMIC, TDK
T2: COILCRAFT