UCC281-3/-5/-ADJ

UCC381-3/-5/-ADJ

SLUS214B -JANUARY 2001

FEATURES

• Precision Positive Linear Voltage

Regulation

• 0.5V Dropout at 1A

• Guaranteed Reverse Input/ Output

Voltage Isolation with Low Leakage

• Low Quiescent Current Irrespective of

Load

• Adjustable Output Voltage Version

• Fixed Versions for 3.3V and 5V

Outputs

• Logic Shutdown Capability

• Short Circuit Power Limit of

3%

• Remote Load Voltage for Accurate

Load Regulation

DESCRIPTION

The UCC381-3/-5/-ADJ family of positive linear series pass regulators is

tailored for low drop out applications where low quiescent power is impor-

tant. Fabricated with a BiCMOS technology ideally suited for low input to

output differential applications, the UCC381 will pass 1A while requiring

only 0.5V of input voltage headroom. Dropout voltage decreases linearly

with output current, so that dropout at 200mA is less than 100mV. Quies-

cent current is always less than 650

µA. To prevent reverse current conduc-

tion, on-chip circuitry limits the minimum forward voltage to typically 50mV.

Once the forward voltage limit is reached, the input-output differential volt-

age is maintained as the input voltage drops until undervoltage lockout dis-

ables the regulator.

UCC381-3 and UCC381-5 versions have on-chip resistor networks preset

to regulate either 3.3V or 5.0V, respectively. Furthermore, remote sensing

of the load voltage is possible by connecting the VOUTS pin directly at the

load. The output voltage is then regulated to 1.5% at room temperature and

better than 2.5% over temperature. The UCC381-ADJ version has a regu-

lated output voltage programmed by an external user-definable resistor ra-

tio.

(continued)

Low Dropout 1 Ampere Linear Regulator Family

1VOUT

2GND

7

GND

R2

R1

+

–

V

PUMP

UVLO

+

–

8

1.3/2.1A

CURRENT

REFERENCE

VIN

UCC381-ADJ

UCC381-3

UCC381-5

R2

R1

0

OPEN

82k

50k

150k

50k

4

3GND

6

GND

1.25V

VOUTS

VOLTAGE

AMPLIFIER

CURRENT

LIMIT

THERMAL

SHUTDOWN

REVERSE VOLTAGE

SENSE

3% DUTY CYCLE

CURRENT LIMIT TIMER

5

0.65V

CT*

SHUTDOWN FOR FIXED VERSIONS

*ADJ

VERSION

ONLY

BLOCK DIAGRAM

UDG-98112