QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 992
MONOLITHIC SYNCHRONOUS BUCK REGULATOR
2
QUICK START PROCEDURE
Demonstration circuit 992 is created to evaluate the
performance of the LTC3549. For proper measure-
ment equipment configuration, set up the circuit ac-
cording to the diagram in Figure 1. Before proceeding
to test, insert jumper JP1 shunt into the off position,
connecting the RUN pin to ground (GND), which
shuts down the circuit. Also insert shunts into the
Pulse-Skip position of jumper JP2, and into the 1.2V
output voltage position.
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 out-
put voltage ripple by touching the probe tip directly
across the Vin or Vout and GND terminals. See
Figure 2 for proper scope probe technique.
1.
Apply 3.6V at Vin and set the load to 50 mA.
Measure Vout; it should read 0V. If desired, one
can measure the shutdown supply current at this
point. The supply current will be approximately 1
uA in shutdown.
2.
Turn on the circuit by inserting the shunt in jumper
JP1 into the ON position. The output voltage
should be regulating. Measure Vout - it should
measure 1.2V +/- 2% (1.176V to 1.224V).
3.
Vary the input voltage from 1.6V to 5.5V and adjust
the load current from 0 to 250 mA. Vout should
read between 1.2V +/- 4% (1.152V to 1.248V).
Measure the output ripple voltage at any output
current level above 50 mA; it will measure less
than 20 mVAC.
The Burst-Mode
TM
and Pulse-Skip
capability of the LTC3549 can also be observed
now by setting the JP2 jumper shunt into either the
Pulse-Skip position or the Burst-Mode
TM
position,
and decreasing the load current below ~40 mA.
4.
Observe the voltage waveform at the switch node.
Verify the switching frequency is between 1.8 MHz
and 2.7 MHz (T = 0.556 us and 0.37 us), and that
the switch node waveform is rectangular in shape.
Insert jumper JP1 shunt into the OFF position and
move the 1.2V Vout shunt into any of the remaining
output voltage options: 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 another +/- 2% tolerance under dynamic line and
load conditions (+/- 4% total). When finished, turn off
the circuit by inserting the jumper JP1 shunt into the
OFF position.
