LT1952IGN Linear Technology, LT1952IGN Datasheet - Page 22

• Manufacturer Part Number: LT1952IGN
• Description: IC,SMPS CONTROLLER,CURRENT-MODE,SOP,16PIN,PLASTIC
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LT1952/LT1952-1
36V to 72V Input, 3.3V 40A Converter
An LT1952-based synchronous forward converter pro-
vides 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 efficien-
cies 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 con-
troller (LTC3900) which results in high efficiency synchro-
nous 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
average power dissipation of the circuit will be lower than
15% of maximum rated power thanks to a soft-start
22
0.22µF
0.1µF
115k
2.2k
59k
13.2k
27k
22k
10k
33k
370k
L1: PA0713, PULSE ENGINEERING
ALL CAPACITORS X7R, CERAMIC, TDK
T2: COILCRAFT
U
7
3
9
5
6
1
2
SD_V
R
BLANK
SS_MAXDC
V
COMP
FB = 1.23V
OSC
R
= 2.5V
36V TO 72V
IN
SEC
U
range. During short circuit the
LT1952
+V
Figure 18. 36V to 72V, 3.3V at 40A Synchronous Forward Converter
IN
DELAY
I
PGND
SENSE
SOUT
GND
W
OUT
V
47k
82k
OC
IN
14
15
8
13
12
11
10
16
V
U1
18V
BAT760
U
470Ω
39k
BCX55
12V
V
U1
1µF
220pF
BAS516
2.2µF
Si7846
0.1µF
10mΩ
controlled hiccup mode. This allows a significant reduc-
tion in power component sizing using the LT1952-based
converter.
PA0912.002
Figure 17. LT1952-Based Synchronous Forward Converter
•
•
•
Efficiency vs Load Current (For Circuit in Figure 18)
V
U1
1nF
Q4470-B
1µF
• •
T2
94
93
92
91
90
89
88
87
86
BIAS
8V
PS2801
0
Q2
PH3230
2x
560Ω
5
6
4
8
10
FG
GND
V
SYNC
CC
270Ω
LTC3900
BIAS
OUTPUT CURRENT (A)
8V
PH3230
TIMER
20
CS
CS
Q3
2x
LT1797
CG
+
–
15k
2.2nF
1
3
1
2
7
BIAS
30
8V
5
2
249k
18k
V
V
f
OSC
1nF
–
+
IN
OUT
L1
4
3
= 48V
40
10k
= 300kHz
= 3.3V
10k
10k
80.6k
1µF
1952 F17
10k
50
LT1009
8
4
C
100µF
3x
OUT
10k
0.1µF
1952 F18
V
3.3V, 40A
OUT
19521fb