UCC284–5, UCC284–12, UCC284–ADJ, UCC384–5, UCC384–12, UCC384–ADJ

LOW-DROPOUT 0.5-A NEGATIVE LINEAR REGULATOR

SLUS234D – JANUARY 2000 – REVISED FEBRUARY 2002

6

POST OFFICE BOX 655303

APPLICATION INFORMATION

programming the output voltage on the UCC384 (continued)

UDG–99029

5

4

1

3

2

R1

R2

VOUT

VOUTS

GND

6

7

VIN

VIN

VIN

VIN

CIN

VIN

8

CT

SD/CT

COUT

VOUT

+

+

(+)

(–)

(+)

(–)

C1

UCC384–ADJ

1

µF

4.7

µF

0.015

µF

Figure 1. Typical Application Circuit

For the UCC384–ADJ, the output voltage is programmed by the following equation:

VOUT

+* 1.25

1

) R1

R2

(1)

When R1 or R2 are selected to be greater than about 100 k

Ω, a small ceramic capacitor should be placed across

R1 to cancel the input pole created by R1 and the parasitic capacitance appearing on VOUTS. Values of

approximately 20 pF should be adequate.

dropout performance

The UCC384 is tailored for low-dropout applications where low-quiescent power is important. Fabricated with

a BCDMOS technology ideally suited for low input-to-output differential applications, the UCC384 passes 0.5 A

while requiring only 0.2 V of headroom. The dropout voltage is dependent on operating conditions such as load

internal charge-pump that drives the MOSFET gate.

Figure 2 shows typical dropout voltages versus output voltage for the UCC384-5 V and -12 V versions as well

as the UCC384–ADJ version programmed between –3.3 V and –15 V. Since the dropout voltage is also affected

by output current, Figure 3 shows typical dropout voltages versus load current for different values of VOUT.

dropout voltages for the UCC384 over temperature under a full load of 0.5 A.

short-circuit protection

The UCC384 provides unique short-circuit protection circuitry that reduces power dissipation during a fault.

When an overcurrent condition is detected, the device enters a pulsed mode of operation, limiting the output

to a 2.5% duty cycle. This reduces the heat sink requirements during a fault. The operation of the UCC384 during

an overcurrent condition is shown in Figure 5.