LP2950
Figure 22. Regulator with Early Warning and Auxiliary Output
+V
in
8
V
D2
in
1
2
Memory
V+
5
3
V
Error
out
D1
1.0 µF
20
SNS
LP2951CN
#1
3.6 V
NiCad
6
NC
SD
V T
O
Gnd FB
4
7
Early Warning
Reset
27 k
All diodes are 1N4148.
D3
Early Warning flag on low input voltage.
µP
2.7 M
Main output latches off at lower input
voltages.
D4
V
DD
Q1
2N3906
8
V
in
Battery backup on auxiliary output.
330 k
1
2
5
3
Operation: Regulator #1’s V
programmed one diode drop above 5.0 V.
is
out
V
Error
out
Main
Output
Its error flag becomes active when V < 5.7
V. When V drops below 5.3 V, the error
in
flag of regulator #2 becomes active and via
in
SNS
LP2951CN
#2
1.0 µF
Q1 latches the main output “off”. When V
6
in
SD
V T
O
again exceeds 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 23. 2.0 A Low Dropout Regulator
+V
in
Current Limit
Section
0.05
470
680
2N3906
1000 µF
2N3906
MJE2955
.33 µF
10 k
4.7 M
8
V
in
1
2
Error
Flag
5
3
V
Error
out
V
out
@ 2.0 A
NC 47
NC
SNS
LP2951CN
220
6
4.7 µF
Tant
SD
V T
O
100 µF
R1
Gnd FB
20 k
.01 µF
4
7
R2
0.033 µF
V
= 1.25V (1.0 + R1/R2)
out
For 5.0 V output, use internal resistors. Wire Pin 6 to 7,
and wire Pin 2 to +V
out
Bus.
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