LT1171HVC datasheet(10/20 Pages) LINER

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LT1170/LT1171/LT1172

Flyback Converter

LCD Contrast Supply

1170/1/2 TA03

2000

µF

C4*

100

µF

0.15

µF

3.74k

1.24k

VIN

20V TO 30V

1.5k

*REQUIRED IF INPUT LEADS

≥ 2"

LT1170

VIN

VSW

OPTIONAL

FILTER

µH

100

µF

VOUT

VSNUB

CLAMP TURN-ON

SPIKE

PRIMARY FLYBACK VOLTAGE =

LT1170 SWITCH VOLTAGE

AREA “a” = AREA “b” TO MAINTAIN

ZERO DC VOLTS ACROSS PRIMARY

SECONDARY VOLTAGE

AREA “c” = AREA “d” TO MAINTAIN

ZERO DC VOLTS ACROSS SECONDARY

PRIMARY CURRENT

SECONDARY CURRENT

LT1170 SWITCH CURRENT

SNUBBER DIODE CURRENT

VOUT + Vf

VIN

VOUT + Vf

N • VIN

∆I

IPRI

IPRI/N

IPRI

t =

(IPRI)(LL)

VSNUB

N* = 1/3

25V

MUR110

GND

0.047

µF

VOUT

–10V TO –26V

1170/1/2 TA04

15k

OPTIONAL

SHUTDOWN

100k

200k

µF

TANTALUM

1N914

0.0047

µF

C2***

µF

TANTALUM

VN2222

5V*

L1**

µH

VBAT*

3V TO 20V

VIN

VSW

LT1172

GND

***

D2, D3 = ER82.004 600mA SCHOTTKY. OTHER FAST SWITCHING TYPES MAY BE USED.

VIN AND BATTERY MAY BE TIED TOGETHER. MAXIMUM VALUE FOR VBAT IS EQUAL TO THE NEGATIVE OUTPUT + 1V. WITH HIGHER

BATTERY VOLTAGES, HIGHEST EFFICIENCY IS OBTAINED BY RUNNING THE LT1172 VIN PIN FROM 5V. SHUTTING OFF THE 5V SUPPLY

WILL AUTOMATICALLY TURN OFF THE LT1172. EFFICIENCY IS ABOUT 80% AT IOUT = 25mA.

R1, R2, R3 ARE MADE LARGE TO MINIMIZE BATTERY DRAIN IN SHUTDOWN, WHICH IS APPROXIMATELY VBAT /(R1 + R2 + R3).

FOR HIGH EFFICIENCY, L1 SHOULD BE MADE ON A FERRITE OR MOLYPERMALLOY CORE. PEAK INDUCTOR CURRENTS ARE ABOUT

600mA AT POUT = 0.7Ω. INDUCTOR SERIES RESISTANCE SHOULD BE LESS THAN 0.4Ω FOR HIGH EFFICIENCY.

OUTPUT RIPPLE IS ABOUT 200mVP-P TO 400mVP-P WITH C2 = 2µF TANTALUM. IF LOWER RIPPLE IS DESIRED, INCREASE C2, OR ADD

A 10

Ω , 1µF TANTALUM OUTPUT FILTER.

TYPICAL APPLICATIO S

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