UCC3912
APPLICATION INFORMATION (cont.)
UDG-93019-4
Figure 2. Load current, timing capacitor voltage, and output voltage of the UCC3912 under Fault conditions.
Estimating Maximum Load Capacitance
For hot swap applications, the rate at which the total
output capacitance can be charged depends on the
maximum output current available and the nature of the
load. For a constant-current current-limited controller,
the output will come up if the load asks for less than the
maximum available short-circuit current.
To guarantee recovery of a duty-cycle from a
short-circuited load condition, there is a maximum total
output capacitance which can be charged for a given
unit ON time (Fault time). The design value of ON or
Fault time can be adjusted by changing the timing ca-
pacitor C
T
.
For worst-case constant-current load of value just less
than the trip limit; C
OUT(max)
can be estimated from:
where V
OUT
is the output voltage.
For a resistive load of value RL, the value of C
OUT(max)
can
be estimated from:
3
28
•
10
•
CT
C
OUT
(
max
)
≈
1
RL
•
l
n
V
OUT
1
−
I
MAX
•
RL
C
OUT
(max)
≈
(
I
MAX
28
•
10
3
•
CT
−
I
LOAD
)
•
V
OUT
5
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