2
dc1736af
DEMO MANUAL DC1736A
QUICK START PROCEDURE
Demonstration circuit 1736A is easy to set up to evalu-
ate the performance of the LT3975. Refer to Figure 2 for
proper measurement equipment setup and follow the
procedure below:
NOTE. When measuring the input or output voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. Measure the input or output voltage
ripple by touching the probe tip directly across the V
IN
or V
OUT
and GND terminals. See Figure 3 for the proper
scope technique.
1. Place JP1 on the ON position.
2. Place JP2 on the RT FREQ position.
3. With power off, connect the input power supply to V
IN
and GND.
4. With power off, connect load from V
OUT
to GND.
5. Turn on the power at the input.
NOTE. Make sure that the input voltages do not exceed 42V.
6. Check for the proper output voltage (3.3V).
NOTE. If there is no output, temporarily disconnect the load
to make sure that the load is not set too high or is shorted.
7. Once the proper output voltages are established, adjust
the load within the operating ranges and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
8. An external clock can be added to the SYNC terminal
when SYNC function is used (JP2 on the SYNC posi-
tion). Please make sure that the SYNC frequency is at
least 20% higher than the set switching frequency. See
the data sheet section Synchronization.
LOAD CURRENT (A)
0
EFFICIENCY (%)
65
70
75
1.5
2.5
DC1735A F01
60
55
50
0.5
1
2
80
85
90
V
OUT
= 3.3V
V
IN
= 12V
f
SW
= 600kHz
Figure 1. Efficiency vs Load Current
