3
DEMO MANUAL DC2787A
Rev. 0
QUICK START PROCEDURE
Demonstration circuit 2787A is easy to set up to evaluate
the performance of the LTC7821. Refer to Figure 2 for
the proper measurement equipment setup and follow the
procedure below.
1. With power off, connect the input power supply to V
IN
(40V-60V) and GND (input return).
2. Connect the output loads between V
OUT
and GND
(Initial load: no load)
3. Connect the DVMs to the input and output.
4. Check the default jumper/switch position: SW1 (RUN):
OFF; JP2 (BIAS): ON.
5. Turn on the input power supply and adjust voltage to 48V;
NOTE. Make sure that the input voltage does not exceed 60V.
6. Turn on the switches: SW1: ON.
7. Check for the proper output voltages from
to VO_SNS−.
8. Once the proper output voltage is established, adjust
the loads within the operating range and measure the
efficiency, output ripple voltage and other parameters.
9. After completing all tests, adjust the load to 0A, power
off the input power supply.
Notes:
1. When measuring the output or input voltage ripple, do
not use the long ground lead on the oscilloscope probe.
See Figure 3 for the proper scope probe technique. Short,
stiff leads need to be soldered to the (+) and (−) terminals
of an output capacitor. The probe’s ground ring needs to
touch the (−) lead and the probe tip needs to touch the
(+) lead.
2. When doing the load step test with the on-board
dynamic load circuit, please make sure the load step-up
pulse duty cycle does not exceed 2% and the pulse dura-
tion is less than 500µs so that the temperature of the
MOSFETs Q20, Q21 in the dynamic load circuit stay in the
safe region. Instead of using the on-board dynamic load
circuit, an electric load can also be used for the load step
test, which does not have the 2% max duty cycle limit for
the load step.
