LP2950, LP2951, NCV2951
+V
in
8
V
in
Error
5
V
out
1
2
D1
D2
1.0
mF
20
Memory
V+
3.6 V
NiCad
NC
SNS
LP2951CN
3
#1
6
SD
V
O
T
GND FB
4
7
27 k
Early Warning
D3
Reset
mP
All diodes are 1N4148.
Early Warning flag on low input voltage.
Main output latches off at lower input voltages.
Battery backup on auxiliary output.
V
out
1
Main
Output
1.0
mF
Operation: Regulator #1’s V
out
is programmed one
diode drop above 5.0 V. Its error flag becomes active
when V
in
< 5.7 V. When V
in
drops below 5.3 V, the
error flag of regulator #2 becomes active and via Q1
latches the main output “off”. When V
in
again exceeds
5.7 V, regulator #1 is back in regulation and the early
warning signal rises, unlatching regulator #2 via D3.
2.7 M
Q1
2N3906
D4
330 k
5
Error
8
V
in
V
DD
2
SNS
LP2951CN
#2
3
6
SD
V
O
T
GND
4
FB
7
Figure 25. Regulator with Early Warning and Auxiliary Output
Current Limit
Section
680
2N3906
2N3906
470
+V
in
0.05
1000
mF
MJE2955
10 k
4.7 M
Error
Flag
5
Error
8
V
in
V
out
1
2
NC
47
4.7
mF
Tant
R1
V
out
@ 2.0 A
100
mF
.33
mF
SNS
LP2951CN
220
20 k
3
SD
V
O
T
6 NC
.01
mF
GND FB
4
7
0.033
mF
V
out
= 1.25V (1.0 + R1/R2)
R2
For 5.0 V output, use internal resistors. Wire Pin 6 to 7,
and wire Pin 2 to +V
out
Bus.
Figure 26. 2.0 A Low Dropout Regulator
http://onsemi.com
12
ONSEMI [ ON SEMICONDUCTOR ]
