LT1949 LINER [Linear Technology], LT1949 Datasheet - Page 6

• Manufacturer Part Number: LT1949
• Description: 600kHz, 1A Switch PWM DC/DC Converter
• Manufacturer: LINER [Linear Technology]

OPERATIO
APPLICATIONS
LT1949
Low-Battery Detector
The LT1949’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
ment as a low-battery detector is straightforward.
6
5% reference. The positive input is the LBI pin. Arrange-
Figure 5. Setting Low-Battery Detector Trip Point
R1
R2
100k
LBI
U
GND
U
200mV
INTERNAL
REFERENCE
–
+
V
IN
INFORMATION
U
LT1949
LBO
1949 F05
GROUND PLANE
Figure 4. Recommended Component Placement for Boost
Converter. Note Direct High Current Paths Using Wide PC
Traces. Minimize Trace Area at Pin 1 (V
Use Multiple Vias to Tie Pin 4 Copper to Ground Plane. Use
Vias at One Location Only to Avoid Introducing Switching
Currents into the Ground Plane
SHUTDOWN
W
3.3V
MULTIPLE
R1
VIAs
1M
R1 =
R2
GND
V
TO PROCESSOR
LB
U
– 200mV
2 A
1
2
3
4
LT1949
C2
LBI
LBO
Figure 5 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 6. The low-battery detector remains active in
shutdown.
8
7
6
5
V
C1
OUT
+
C
) and Pin 2 (FB).
200mV
Figure 6. Accessing 200mV Reference
V
2N3906
REF
V
L1
IN
10k
1949 F04
+
200k
10 F
LBO
LBI
LT1949
GND
V
IN
1949 F06