QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 993
500MA, 2.25 MHZ SYNCHRONOUS STEP-DOWN REGULATOR
2
QUICK START PROCEDURE
Demonstration Circuit 993 is easy to set up to evalu-
ate the performance of the LTC3542. For proper
measurement equipment configuration, set up the
circuit according to the diagram in
Figure 1
. Before
proceeding to test, insert shunts into the OFF position
of header JP3, which connects the RUN pin to ground
(GND), and thus, shuts down the circuit, and the 1.2V
output voltage header – JP4.
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 volt-
age 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 DC993 set up according to the proper meas-
urement and equipment in
Figure 1
, apply 3.3V at Vin
(Do not hot-plug Vin or increase Vin over the rated
maximum supply voltage of 5.5V, or the part may be
damaged.). Measure Vout; it should read 0V. If de-
sired, one can measure the shutdown supply current
at this point. The supply current will be approxi-
mately 1 uA, or less, in shutdown.
Turn on the circuit by inserting the shunt in header
JP3 into the ON position. The output voltage should
be regulating. Measure Vout - it should measure
1.2V +/- 2% (1.176V to 1.224V).
Vary the input voltage from 2.5V to 5.5V and adjust
the load current from 0 to 500 mA. Vout should read
between 1.2V +/- 4% (1.152V to 1.248V).
Measure the output ripple voltage at any output cur-
rent level; it usually will measure less than 30 mVAC.
Observe the voltage waveform at the switch node.
Verify the switching frequency is between 1.8 MHz
and 2.7 MHz (T = 0.555 us and 0.37 us), and that the
switch node waveform is rectangular in shape.
Insert header JP3 shunt into the OFF position and move
the 1.2V Vout shunt into any of the two remaining output
voltage option headers: 1.5V or 1.8V. Just as in the
1.2Vout test, the output voltage should read Vout +/- 2%
tolerance under static line and load conditions, and +/-
1% tolerance under dynamic line and load conditions
(+/- 2% total).
When finished, turn off the circuit by inserting the
shunt in header JP3 into the OFF position (connecting
the RUN pin to ground).