2
dc1864af
DEMO MANUAL DC1864A
QUICK START PROCEDURE
Demonstration circuit 1864 is easy to set up to evaluate the
performance of the LTC3621-2. For proper measurement
equipment configuration, set up the circuit according to
the diagram in Figure 1. Before proceeding to test, check
that the shunts are inserted into the correct locations:
1.2V position of the output voltage header JP3, into the
BM (Burst Mode operation) position of MODE header JP2,
and into the ON position of RUN header JP1.
When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscil
-
loscope probe.
Measure the input or output voltage ripple
by touching the probe tip directly across the VIN or VOUT
and GND terminals. See Figure 2 for proper scope probe
measurement technique.
With the DC1864 set up according to the proper measure
-
ment configuration
and equipment in Figure 1, apply 5V at
VIN (Do not hot-plug VIN or increase VIN over the rated
maximum supply voltage of 17V, or the part may be dam
-
aged.). Measure V
OUT
; it should read 1.2V. (If desired, the
quiescent current of the circuit can be monitored now by
swapping the shunt in header JP1 into the OFF position.)
The
output voltage should be regulating. Draw 500mA out
of the output and measure V
OUT
— it should measure 1.2V
±2% (1.176V to 1.224V). Verify the switching frequency
is between 1.8MHz and 2.6MHz (t = 55ns and 38ns), and
that the switch node waveform is rectangular in shape.
Vary the input voltage from 2.7V to 17V and the load cur
-
rent from
0
to 1A. V
OUT
should regulate around 1.2V ±3%
(1.164V to 1.236V). Measure the output ripple voltage; it
should measure less than 20mV AC.
Set the input voltage to 12V and the output current to than
100mA. Observe the Burst Mode operation at the switch
node (the pad of the inductor opposite from the output),
and measure the output ripple voltage. It should measure
less than 100mV. Change the shunt position on the MODE
header from BM to PS (pulse-skipping mode) and observe
the voltage waveform at the switch pins. To achieve forced
continuous operation, insert two 100k resistors at the
pads for R1 and R2. These resistors develop a voltage of
INTV
CC
/2 at the MODE pin, which is the voltage setting
for forced continuous operation.
Insert the JP1 shunt into the OFF position and move the
shunt in
the 1.2V output JP3 header into any of the re-
maining output
voltage option headers: 1.8V (JP4), 2.5V
(JP5), 3.3V (JP6) or 5V (JP7). Just as in the 1.2V V
OUT
test, the output voltage should read V
OUT
±2% tolerance
under static line and load conditions and ±1% tolerance
under dynamic line and load conditions (±3% total). Also,
the circuit switch operation in Burst or pulse-skipping
mode operation will remain the same. There is an extra
output voltage header, JP8, to allow the user to easily set
the output to their desired value
When finished, turn off the circuit by inserting the shunt
in header JP1 into the OFF position.
