
SLUS317B JANUARY 2000 REVISED FEBRUARY 2004
5
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
pin descriptions (continued)
Figure 1
DROPOUT VOLTAGE (V
B
V
OUT
)
vs
LOAD CURRENT
3
IL Load Current A
2
1
0
1.7
1.8
1.9
1.6
V
TJ = 27 C
Figure 2
DROPOUT VOLTAGE (V
IN
V
OUT
)
vs
LOAD CURRENT
3 A
2 A
1 A
100 mA
100
200
300
400
IL - Load Current - A
V
TJ = 27 C
APPLICATION INFORMATION
The UC382 is easy to use. The adjustable version requires two 0.1% resistors to set the output voltage. The
fixed versions of the UC382 require no external resistors. All versions of the UC382 require decoupling
capacitors on the input and output. In a typical application, VB and VIN are driven from switching power supplies
which may have large filter capacitors at their outputs. If the UC382 is further than 12 inches from the power
supply, it is recommended to add local decoupling as close as possible to the linear regulator.
Decouple the output of the UC382 with at least 100
μ
F of high-quality tantalum or Sanyo OSCON capacitors
close to the VOUT pin for maximum stability. Many applications involving Ultra-Fast GTL or BTL applications
require additional capacitance close to the load. The exact amount will vary according to speed and magnitude
of the load transients and the tolerance allowed for transients on VOUT. When specifying the decoupling
capacitors, the series resistance of the capacitor bank is an important factor in its ability to filter load transients.
The UC382 allows for Kelvin sensing the voltage at the load. This improves regulation performance and
eliminates the voltage drops due to wire-trace resistance. This voltage drop must be added to the headroom
(VIN to VOUT and VB to VOUT). The dropout of 450 mV is measured at the pins and does not include additional
drops due to trace resistance. The minimum load current is 10 mA.
Two or more UC382’s may be used in parallel. While stable, this arrangement does degrade the transient
response.