LT1614 查看數據表（PDF） - Linear Technology

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LT1614

Inverting 600kHz Switching Regulator

Linear Technology 

LT1614

APPLICATIONS INFORMATION

Shutdown Pin

The LT1614 has a Shutdown pin (SHDN) that must be

grounded to shut the device down or tied to a voltage equal

or greater than VIN to operate. The shutdown circuit is

shown in Figure 13.

Note that allowing SHDN to float turns on both the start-

up current (Q2) and the shutdown current (Q3) for VIN >

2VBE. The LT1614 doesn’t know what to do in this situation

and behaves erratically. SHDN voltage above VIN is al-

lowed. This merely reverse-biases Q3’s base emitter junc-

tion, a benign condition. The low-battery detector is dis-

abled when SHDN is low.

VIN

SHDN

R2

400k

200k

Q1

Q3

SHUTDOWN

CURRENT

START-UP

CURRENT

Q2

1614 F13

Figure 13. Shutdown Circuit

Low-Battery Detector

The LT1614’s low-battery detector is a simple PNP input

gain stage with an open collector NPN output. The nega-

tive input of the gain stage is tied internally to a 200mV

reference. The positive input is the LBI pin. Arrangement

as a low-battery detector is straightforward. Figure 14

details hookup. R1 and R2 need only be low enough in

value so that the bias current of the LBI pin doesn’t cause

large errors. For R2, 100k is adequate. The 200mV refer-

ence can also be accessed as shown in Figure 15. The low-

battery detect is not operative when the device is shut

down.

R1

LBI

R2

100k

VIN

+

–

LT1614

LBO

3.3V

1M

TO PROCESSOR

200mV

INTERNAL

REFERENCE

GND

1614 F14

R1 = VLB – 200mV

2µA

Figure 14. Setting Low-Battery Detector Trip Point

200k

2N3906

VREF

200mV

+

10k

10µF

VIN

LBO

LT1614

LBI

GND

1614 F15

Figure 15. Accessing 200mV Reference

Coupled Inductors

The applications shown in this data sheet use two un-

coupled inductors because the Murata units specified are

small and inexpensive. This topology can also be used

with a coupled inductor as shown in Figure 16. Be sure to

get the phasing right.

VIN

5V

+

L1A

10µH •

C1

33µF

100k

VIN

SW

SHDN

LT1614

VC

NFB

GND

1nF

C3

1µF

L1B

• 10µH

69.8k

D1

24.9k

C1, C2: AVX TAJB336M010

C3: AVX 1206CY106

D1: MBR0520

L1: COILTRONICS CTX10-1

VOUT

– 5V

200mA

C2

33µF

1614 F16

Figure 16. 5V to – 5V Converter with Coupled Inductor

11

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