Linear Technology DC1317A-B Quick Start Manual page 4

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
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
95%
93%
91%
89%
87%
85%
83%
0
Figure 3. High efficiency of DC1317A Figure 3. High efficiency of DC1317A Figure 3. High efficiency of DC1317A- - - - B a Figure 3. High efficiency of DC1317A
the board to be used in thermally critical appl the board to be u the board to be u the board to be u
cations cations
cations cations
OUTPUT LOAD STEP RES OUTPUT LOAD STEP RES OUTPUT LOAD STEP RES OUTPUT LOAD STEP RESPONSE
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.
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24V input
48V input
10 20
Iout [A]
B al l l l lows B a B a
sed in thermally critical appli- i- i- i- sed in thermally critical appl sed in thermally critical appl
PONSE PONSE PONSE
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
s s s s u u u u perior 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 capaci i i i tors. without the additional output capac
without the additional output capac without the additional output capac
SOFT START FUNCTION SOFT START FUNCTI SOFT START FUNCTI SOFT START FUNCTI
The DC1317 features LT4430 opto coupler driver
30
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
lows lows lows
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 pro- o- o- o- Figure 5. The LT4430 opto coupler driver pr Figure 5. The LT4430 opto coupler driver pr
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 out t t t put voltage overshoot. without ou without ou without ou
DEBUGGING AND TESTING G G G DEBUGGING AND TESTIN DEBUGGING AND TESTIN DEBUGGING AND TESTIN
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
ON ON ON
put voltage overshoot. put voltage overshoot. put voltage overshoot.
tors.
tors. tors.
4