11

LT1317/LT1317B

Single Li-Ion Cell to 3.3V SEPIC Converter

TYPICAL APPLICATIO S

LOW-BATTERY DETECTOR

The LT1317’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

±5% reference. The positive input is the LBI pin. Arrange-

ment as a low-battery detector is straightforward.

Figure 11 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 reference can also be accessed as shown in

Figure 12. The low-battery detector remains active in

shutdown.

Figure 12. Accessing 200mV Reference

LT1317

LBI

LBO

200k

10

µF

GND

10k

1317 F12

2N3906

200mV

+

LBO

LBI

TO PROCESSOR

R1

1M

R2

100k

LT1317

1317 F11

3.3V

GND

200mV

INTERNAL

REFERENCE

–

+

R1 =

2

µA

Figure 11. Setting Low-Battery Detector Trip Point

3.3V SEPIC Efficiency

SW

FB

LT1317

L1A*

C3

1

µF

L1B*

MBR0520

SHDN

33k

604k

1%

3.3V

250mA

1M

1%

3300pF

1317 TA03

C1, C2: AVX TPSC476M010

C3: AVX 1206YC106KAT

* COILTRONICS CTX20-1

GND

SINGLE

Li-ION

CELL

(2.7V TO

4.2V)

C1

47

µF

+

C2

47

µF

+

LOAD CURRENT (mA)

1

80

75

70

65

60

55

50

10

100

1000

1317 TA03a