QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
4
and small size. To achieve such high efficiency all of
the power components were carefully selected.
Please consult LT factory for assistance if any
changes to the circuit are required.
DC1317A-B (LT1952) 5V Output Efficiency
83%
85%
87%
89%
91%
93%
95%
0
10
20
30
Iout [A]
24V input
48V input
Figure 3. High efficiency of DC1317A
Figure 3. High efficiency of DC1317A
Figure 3. High efficiency of DC1317A
Figure 3. High efficiency of DC1317A----B a
B a
B a
B alllllows
lows
lows
lows
the board to be u
the board to be u
the board to be u
the board to be used in thermally critical appl
sed in thermally critical appl
sed in thermally critical appl
sed in thermally critical appli-
i-
i-
i-
cations
cations
cations
cations
OUTPUT LOAD STEP RES
OUTPUT LOAD STEP RES
OUTPUT LOAD STEP RES
OUTPUT LOAD STEP RESPONSE
PONSE
PONSE
PONSE
The load step response of DC1317A-B, shown in
Figure 4, is very fast even though relatively small
amount of output capacitance is present (300uF
ceramic and 470uF electrolytic). This is thanks to
fast error amplifier of LT4430, optimal amount of
current slope compensation of LT1952, fast opto
coupler and fast error amplifier of LT1952. If higher
load steps need to be handled more output capaci-
tance can be added in order to keep the voltage
transients at the desired level. Also, the loop re-
sponse can be improved further by faster loop
compensation.
Figure 4. Fast transient response of DC1317 is
Figure 4. Fast transient response of DC1317 is
Figure 4. Fast transient response of DC1317 is
Figure 4. Fast transient response of DC1317 is
ssssu
uu
uperior to many competing power modules
perior to many competing power modules
perior to many competing power modules
perior to many competing power modules
without the additional output capac
without the additional output capac
without the additional output capac
without the additional output capaciiiitors.
tors.
tors.
tors.
SOFT START FUNCTI
SOFT START FUNCTI
SOFT START FUNCTI
SOFT START FUNCTION
ON
ON
ON
The DC1317 features LT4430 opto coupler driver
that has soft start function which produces mono-
tonic startup ramp shown if Figure 5. 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 5. The LT4430 opto coupler driver pr
Figure 5. The LT4430 opto coupler driver pr
Figure 5. The LT4430 opto coupler driver pr
Figure 5. The LT4430 opto coupler driver pro-
o-
o-
o-
duces monotonic output voltage rise at startup
duces monotonic output voltage rise at startup
duces monotonic output voltage rise at startup
duces monotonic output voltage rise at startup
without ou
without ou
without ou
without outtttput voltage overshoot.
put voltage overshoot.
put voltage overshoot.
put voltage overshoot.
DEBUGGING AND TESTIN
DEBUGGING AND TESTIN
DEBUGGING AND TESTIN
DEBUGGING AND TESTING
G
G
G
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
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