Datasheet

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
SLUS215B − OCTOBER 1998 − REVISED FEBRUARY 2004
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
PEAK
CURRENT
LIMIT
OVER−
CURRENT
THRESHOLD
OVERLOAD
OUTPUT
CURRENT
IO (NOM)
V
O
(NOM)
R
OL
I
CL
OUTPUT
VOLTAGE
T
ON
T
ON
32 T
ON
32 T
ON
T
ON
32 T
ON
Figure 1. UCC383 Short-Circuit Timing
A capacitive load on the regulator’s output appears as a short-circuit during start-up. If the capacitance is too
large, the output voltage does not come into regulation during the initial t
ON
period and the UCC383 enters
pulsed mode operation. The peak current limit, t
ON
period, and load characteristics determine the maximum
value of output capacitor that can be charged. For a constant current load the maximum output capacitance is
given as follows:
C
OUT(max)
+
ǒ
I
CL
* I
LOAD
Ǔ
t
ON
V
OUT
Farads
For worst case calculations, the minimum values of on time (t
ON
) and peak current limit (I
CL
) should be used.
The adjustable version allows the t
ON
time to be adjusted with a capacitor on the CT pin:
t
ON(adj)
+ 750, 000 C
(
m Farad
)
microseconds
For a resistive load (R
LOAD
) the maximum output capacitor can be estimated from:
C
OUT(max)
+
t
ON(sec)
R
LOAD
ȏn
ȧ
ȡ
Ȣ
1
1*
VOUT
I
CL
R
LOAD
ȧ
ȣ
Ȥ
Farads
(1)
(2)
(3)