LT1952/LT1952-1

21

19521fd

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

96.0

95.5

95.0

94.5

94.0

93.5

93.0

10

12

14

8

616

18

20

1952 F15

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

220pF

8V

BIAS

3

FG

5

CG

36V TO 72V

T1

PA0815.002

BAS516

BCX55

12V, 20A

10k

10k

10k

1nF

1μF

15k

560W

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