LT1952 데이터 시트보기 (PDF) - Linear Technology

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LT1952

Single Switch Synchronous Forward Controller

Linear Technology 

LT1952/LT1952-1

APPLICATIONS INFORMATION

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 VIN

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.

This allows a significant reduction in power component

sizing using the LT1952-based converter.

94

93

92

91

90

89

88

87

VIN = 48V

VOUT = 3.3V

86

fOSC = 300kHz

0

10

20

30

40

50

OUTPUT CURRENT (A)

1952 F17

Figure 17. LT1952-Based Synchronous Forward Converter

Efficiency vs Load Current (For Circuit in Figure 18)

0.22µF

0.1µF

+VIN

36V TO 72V

VU1

47k

82k

18V

BCX55

12V

PA0912.002

••

BAS516

0.1µF

Q2

PH3230

2x

Q3

PH3230

2x

L1

COUT

100µF

10k

3x

2.2mF

370k

13.2k

115k

27k

7

SD_VSEC

3

ROSC

9 BLANK LT1952

5

SS_MAXDC

59k 10k

6

33k

VR = 2.5V

1

COMP

2

FB = 1.23V

14

OUT

15

VIN

GND 8

13

PGND

DELAY 12

11

OC

10

ISENSE

16

SOUT

22k

2.2k

VU1

Si7846

BAT760

39k

1µF

10mΩ

470Ω

220pF

L1: PA0713, PULSE ENGINEERING

ALL CAPACITORS X7R, CERAMIC, TDK

T2: COILCRAFT

•

LTC3900

5 FG

CG 3

6 GND

CS+ 1

10k

1mF

4 VCC

CS– 2

10k

8V 8 SYNC TIMER 7

BIAS

15k

1nF

1nF

560Ω

8V

BIAS

249k 80.6k

T2

Q4470-B

VU1

PS2801

8V

BIAS

2.2nF

18k

270Ω

5

1

LT1797 2

4

10k

3 10k

1µF 8

VOUT

3.3V, 40A

0.1µF

4

LT1009

1952 F18

Figure 18. 36V to 72V, 3.3V at 40A Synchronous Forward Converter

19521fe

23

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