5

UCC281-3/-5/-ADJ

UCC381-3/-5/-ADJ

Overview

The UCC381 family of low dropout linear (LDO) regula-

tors provide a regulated output voltage for applications

with up to 1A of load current. The regulator features a

low dropout voltage and short circuit protection, making

their use ideal for demanding high current applications

requiring fault tolerance.

Short Circuit Protection

The UCC381 provides unique short circuit protection

circuitry that reduces power dissipation during a fault.

When an overload situation is detected, the device en-

ters a pulsed mode of operation at 3% duty cycle re-

ducing the heat sink requirements during a fault. The

UCC381 has two current thresholds that determine its

behavior during a fault as shown in Fig. 1.

When the regulator current exceeds the Overcurrent

rent Limit, the regulator limits the current to peak cur-

is nominally 1 Amp greater than the overcurrent thresh-

old. The regulator will continue in pulsed mode until the

fault is cleared as illustrated in Fig. 1.

A capacitive load on the regulator’s output will appear as a

short circuit during start-up. If the capacitance is too large,

the output voltage will not come into regulation during the

characteristics determine the maximum value of output ca-

pacitor that can be charged. For a constant current load

the maximum output capacitance is given as follows:

CI

I

T

V

Farads

OUT

CL

LOAD

ON

OUT

max

=−

•

(1)

For worst case calculations the minimum values of on time

capacitor on the CT pin:

(

)

T

C

Farads

ON adj

µµ

sec

,

=•

660 000

(2)

can be estimated from:

()

C

T

Rn

V

IR

OUT

ON

LOAD

OUT

CL

LOAD

max

=

•

−

•



























l

1

1















Farads

(3)

APPLICATION INFORMATION

32T

ON

T

ON

T

ON

T

ON

32T

ON

32T

ON

V

O

(nom)

OUTPUT

VOLTAGE

I

OUTPUT

CURRENT

R

PEAK CURRENT

LIMIT

OVERCURRENT

THRESHOLD

OVERLOAD

Figure 1. UCC381 short circuit timing.

UDG-98150