Soft Start Function - Linear Technology DC1317A Quick Start Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
DC1317A-G-18V 18V Output Efficiency,
95%
94%
93%
92%
91%
90%
89%
0 1
Figure 4. The efficiency of modified DC1317A-G
demo board for 18V output.
OUTPUT LOAD STEP RESPONSE
The load step response of DC1317A-G is very fast
even though relatively small amount of output ca-
pacitance is present (200uF ceramic and 220uF
electrolytic). This is thanks to fast error amplifier of
LT4430, optimal amount of current slope compen-
sation of LT1952, fast opto coupler and fast error
amplifier of LT1952. If higher load steps need to be
handled more output capacitance can be added in
order to keep the voltage transients at the desired
level. The load step transients are shown in Figure
5.
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12V input
24V input
2 3 4 5 6 7
Iout [A]
Figure 5. Fast transient response of DC1317A-F is
8
superior to many competing power modules with-
out the additional output capacitors.

SOFT START FUNCTION

The DC1317 features LT4430 opto coupler driver
that has soft start function which produces mono-
tonic startup ramp shown if Figure 6. The rise time
of output voltage is controlled by capacitor C19 that
is connected to OC (Overshoot Control) pin of
LT4430. Also, the soft-start function will prevent
input current surges even with full load at the out-
put.
Figure 6. The LT4430 opto coupler driver pro-
duces monotonic output voltage rise at startup
without output voltage overshoot.
DEBUGGING AND TESTING
The DC1317 can easily be tested and debugged by
powering the bias circuit separately from the main
power circuit. To place DC1317 into debug mode
4