LP2950/2951

Micrel

3

February 1999

3-45

Low Drift Current Source

5 Volt Current Limiter

LP2951

FB

SD

1

3

7

GND

4

VIN

8

OUT

V

SHUTDOWN

INPUT

LOAD

+V = 2 → 30V

IL↓

IL=

1.23

R

0.1

µF

1

µF

1%

R

* MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV,

DEPENDING ON LOAD CURRENT.

LP2950Z

OUT

GND

+V IN

*V

= 5V

OUT

V

+V

1

µF

+

IN

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

ITS ERROR FLAG BECOMES ACTIVE WHEN V

WHEN V

BELOW 5.3 V, THE ERROR FLAG OF REG. #2 BECOMES ACTIVE AND VIA Q1

LATCHES THE MAIN OUTPUT OFF. WHEN V

IS BACK IN REGULATION AND THE EARLY WARNING SIGNAL RISES,

UNLATCHING REG. #2 VIA D3.

LP2951

#1

SENSE

V

ERROR

GND

20

27k

Ω

4

5

1

8

OUT

+VIN

2

LP2951

#2

SENSE

V

ERROR

GND

+

4

5

1

8

OUT

+VIN

2

MEMORY

V+

D 2

D 1

2.7M

Ω

D 3

D 4

330k

Ω

RESET

EARLY WARNING

µP

VDO

SD

3

Q1

1

µf

MAIN

OUTPUT

1

µF

+VIN

3.6V

NICAD