MIC2950/2951
+V = 2
→
30V
I L
↓
LOAD
I L=
1.23V
R
Micrel
5V BUS
+V IN
8
VIN
VOUT
MIC2951
1
V
OUT
MIC2950Z
*V
OUT
≈5V
+
GND
1µF
SHUTDOWN 3 SD
INPUT
OFF
ON
0.1µF
FB
7
R
1%
1µF
GND
4
870 27
5-Volt Current Limiter
* MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,
DEPENDING ON LOAD CURRENT.
Low Drift Current Source
+V IN
8
+V IN
2
SENSE
D1
VOUT
1
D2
MEMORY
V+
20
MIC2951
#1
5
ERROR
GND
4
27kΩ
1µF
3.6V
NICAD
870 29
2.7MΩ
Q1
D4
D3
EARLY WARNING
RESET
8
+V IN
2
SENSE
VOUT
1
330kΩ
MAIN
OUTPUT
µP
VDO
MIC2951
#2
5
3
SD
ERROR
GND
4
+
1µf
Regulator with Early Warning and Auxiliary Output
• EARLY WARNING FLAG ON LOW INPUT VOLTAGE
• MAIN OUTPUT LATCHES OFF AT LOWER INPUT VOLTAGES
• BATTERY BACKUP ON AUXILIARY OUTPUT
OPERATION: REG. #1’S V
OUT
IS PROGRAMMED ONE DIODE DROP ABOVE 5 V.
ITS ERROR FLAG BECOMES ACTIVE WHEN V
IN
≤
5.7 V. WHEN V
IN
DROPS
BELOW 5.3 V, THE ERROR FLAG OF REG. #2 BECOMES ACTIVE AND VIA Q1
LATCHES THE MAIN OUTPUT OFF. WHEN V
IN
AGAIN EXCEEDS 5.7 V REG. #1
IS BACK IN REGULATION AND THE EARLY WARNING SIGNAL RISES,
UNLATCHING REG. #2 VIA D3.
3-60
February 1999
MICREL [ MICREL SEMICONDUCTOR ]
