Datasheet
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 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
programming the output voltage on the UCC384 (continued)
UDG–99029
5
4
1
32
R1
R2
VOUT
VOUTS
GND
6 7
VIN VIN VIN VIN
CIN
VIN
8
CT
SD/CT
COUT
VOUT
+
+
(+)
(–)
(+)
(–)
C1
UCC384–ADJ
1
µ
F
4.7
µ
F
0.015
µ
F
Figure 1. Typical Application Circuit
For the UCC384–ADJ, the output voltage is programmed by the following equation:
VOUT +*1.25
ǒ
1 )
R1
R2
Ǔ
(1)
When R1 or R2 are selected to be greater than about 100 kΩ, 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
current, input and load voltages, and temperature. The UCC384 achieves a low R
DS
(on) through the use of an
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.
Operating temperatures also affect the R
DS
(on) and the dropout voltage of the UCC384. Figure 4 shows typical
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.