Datasheet

LT1952/LT1952-1
22
19521fe
48V to Isolated 12V, 20A (No Opto-Coupler)
‘Bus Converter’
The wide programmable range and accuracy of the
LT1952/LT1952-1 Volt-Second clamp makes the LT1952/
LT1952-1 an ideal choice for ‘Bus Converter’ applications
where the Volt-Second clamp provides line regulation for
the converter output. The 48V to 12V 20A ‘Bus Converter’
application in Figure16 shows a semi-regulated isolated
output without the need for an optocoupler, optocoupler
driver, reference or feedback network. Some ‘Bus Converter’
solutions run with a fixed 50% duty cycle resulting in an
output variation of 2-to-1 for applications with a 72V to
36V input range. The LT1952/LT1952-1 use an accurate
wide programmable range Volt-Second clamp to initially
program and then control power supply output voltage
to typically ±10% for the same 36V to 72V input range.
Efficiency for the LT1952 based bus converter in Figure 16
APPLICATIONS INFORMATION
achieves a high 94% at 20A (Figure 15). The solution is
only slightly larger than 1/4 “brick” size and uses only
ceramic capacitors for high reliability.
LOAD CURRENT (A)
4
EFFICIENCY (%)
96.0
95.5
95.0
94.5
94.0
93.5
93.0
10 12 1486 16 18 20
1952 F15
V
IN
= 48V
V
OUT
= 12V
Figure 15. LT1952-Based Synchronous ‘Bus Converter’
Efficiency vs Load Current (For Circuit in Figure 16)
Figure 16. 36V to 72V Input to 12V at 20A No ‘Optocoupler’ Synchronous ‘Bus Converter’
•
••
••
LTC3900
8V
BIAS
V
U1
V
U1
220pF
8V
BIAS
3
FG
5
CG
V
IN
36V TO 72V
T1
PA0815.002
BAS516
BCX55
V
OUT
12V, 20A
10k
10k
10k
C
T
1nF
1µF
R
T
15k
560W
L1: PA1494.242 PULSE ENGINEERING
T1: PULSE ENGINEERING
T2: COILCRAFT
C
OUT
33µF, 16V
X5R, TDK
3x
0.1µF
2.2µF, 100V
2x
1nF
BAT760
12V
Si7370
2x
PH4840
2x
18V
T2
Q4470-B
82k
47k
1952 F16
2.4µH
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
REF
OC
6 11
COMP I
SENSE
1 10
FB SOUT
2 16
•
PH21NQ15
2x
1
GND
6
CS
+
2
V
CC
4
CS
–
7
SYNC
8
TIMER
370k
9mΩ
1µF
470Ω
39k
13.2k
115k
27k
0.47µF
0.1µF
10k59k