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DEMO MANUAL DC1891A
QUICK START PROCEDURE
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0
1
2
3
Figure 3. Reducing the Input Voltage Range and Selecting
More Optimal MOSFET, Diode and Inductor Can Optimize the
Efficiency of DC1891A
OUTPUT LOAD STEP RESPONSE
The load step response of DC1891A is very fast even
though a relatively small amount of output capacitance
is present (188µF ceramic and 440µF electrolytic). The
load step transients are shown in Figure 4. To improve
load step response further or to reduce the output ripple,
more output capacitance can be added. Low ESR output
capacitors will have the greatest effect on reducing the
ripple and load step transients.
4
6V INPUT
12V INPUT
24V INPUT
48V INPUT
4
5
6
7
8
I
(A)
OUT
DC1891a F03
V
= 12V, V
= 12V
IN
OUT
I
= 1A
OUT
3A LOAD STEP
500µs/DIV
Figure 4. Fast Transient Response of DC1891A is Achieved with a
Small Amount of Output Capacitance
SOFT-START FUNCTION
The DC1891A features a soft-start circuit that controls the
inrush current and output voltage ramp at start-up. The
capacitor C
controls the start-up period. The start-up
SS
waveforms are shown in Figure 5.
V
= 12V, V
= 12V
IN
OUT
I
= 5A
OUT
START-UP
I
2A/DIV
IN
Figure 5. The DC1891A Ramps the Output Slowly at Start-Up
without Generating an Input Current Surge
V
200mV/DIV
OUT
I
2A/DIV
OUT
DC1891a F04
V
2V/DIV
OUT
50ms/DIV
DC1891a F05
dc1891af
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