LT1952

21

1952f

APPLICATIO S I FOR ATIO

Figure 16. 36V to 72V Input to 12V at 20A No ‘Optocoupler’ Synchronous ‘Bus Converter’

Figure 15. LT1952-Based Synchronous ‘Bus Converter’ Efficiency

vs Load Current (For Circuit in Figure 16)

48V to Isolated 12V, 20A (No Opto-Coupler)

‘Bus Converter’

The wide programmable range and accuracy of the LT1952

Volt-Second clamp makes the LT1952 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

uses 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 con-

verter in Figure 16 achieves a high 94% at 20A (Figure 15).

LOAD CURRENT (A)

4

96.0

95.5

95.0

94.5

94.0

93.5

93.0

10

12

14

8

6

161820

1952 F15

The solution is only slightly larger than 1/4 “brick” size and

uses only ceramic capacitors for high reliability.

•

•

•

LTC3900

8V

BIAS

220pF

8V

BIAS

3

FG

5

CG

36V TO 72V

T1

PA0815.002

BAS516

BCX55

12V, 20A

10k

10k

10k

1nF

1µF

15k

560Ω

L1: PA1494.242 PULSE ENGINEERING

T1: PULSE ENGINEERING

T2: COILCRAFT

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

OUT

LT1952

714

315

BLANK

GND

98

SS_MAXDC

PGND

513

DELAY

12

OC

611

COMP

110

FB

SOUT

216

PH21NQ15

2x

1

GND

6

2

4

7

SYNC

8

TIMER

370k

9mΩ

1µF

470Ω

39k

13.2k

115k

27k

0.47µF

0.1µF

10k

59k

12V Bus Converter Efficiency