Datasheet

11
LT1317/LT1317B
APPLICATIONS INFORMATION
WUU
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Single Li-Ion Cell to 3.3V SEPIC Converter
TYPICAL APPLICATIO S
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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
V
IN
LT1317
LBI
LBO
200k
10µF
GND
10k
1317 F12
2N3906
V
REF

200mV
+
LBO
LBI
TO PROCESSOR
R1
1M
R2
100k
V
IN
LT1317
1317 F11
3.3V
GND
200mV
INTERNAL
REFERENCE
–
+
R1 =
V
LB
– 200mV
2µA
Figure 11. Setting Low-Battery Detector Trip Point
3.3V SEPIC Efficiency
V
IN
SW
FB
LT1317
L1A*
C3
1µF
L1B*
MBR0520
SHDN
33k
604k
1%
V
OUT

3.3V
250mA
1M
1%
3300pF
1317 TA03
C1, C2: AVX TPSC476M010
C3: AVX 1206YC106KAT
* COILTRONICS CTX20-1
V
C
GND
SINGLE
Li-ION
CELL
(2.7V TO
4.2V)
C1
47µF
+
C2
47µF
+
LOAD CURRENT (mA)
1
EFFICIENCY (%)
80
75
70
65
60
55
50
10 100 1000
1317 TA03a
V
IN
= 4.2V
V
IN
= 3.5V
V
IN
= 2.7V