LP2950, LP2951, NCV2951
+V
V
in
8
D2
in
1
2
Memory
V+
5
3
V
out
Error
D1
1.0 mF
20
SNS
LP2951CN
#1
3.6 V
NiCad
6
NC
SD
V
O
T
GND FB
4
7
Early Warning
27 k
All diodes are 1N4148.
D3
Reset
Early Warning flag on low input voltage.
Main output latches off at lower input voltages.
Battery backup on auxiliary output.
mP
2.7 M
D4
V
DD
Q1
2N3906
8
330 k
V
in
1
2
5
3
Operation: Regulator #1’s V is programmed one
diode drop above 5.0 V. Its error flag becomes active
V
out
out
Error
Main
Output
when V < 5.7 V. When V drops below 5.3 V, the
in
in
SNS
error flag of regulator #2 becomes active and via Q1
LP2951CN
#2
latches the main output “off”. When V again exceeds
1.0 mF
in
6
SD
V
O
T
5.7 V, regulator #1 is back in regulation and the early
warning signal rises, unlatching regulator #2 via D3.
GND FB
4
7
Figure 25. Regulator with Early Warning and Auxiliary Output
+V
in
Current Limit
Section
0.05
470
680
2N3906
1000 mF
2N3906
MJE2955
.33 mF
10 k
4.7 M
8
V
in
1
2
Error
Flag
5
3
V
out
Error
V
out
@ 2.0 A
NC 47
NC
SNS
LP2951CN
220
6
4.7 mF
Tant
SD
V
O
T
100 mF
R1
GND FB
4
20 k
.01 mF
7
R2
0.033 mF
V
out
= 1.25V (1.0 + R1/R2)
For 5.0 V output, use internal resistors. Wire Pin 6 to 7,
and wire Pin 2 to +V Bus.
out
Figure 26. 2.0 A Low Dropout Regulator
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