Linear DC768 Quick Start Manual page 2

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 768
QUICK START PROCEDURE
Demonstration Circuit 768 is easy to set up to evalu-
ate the performance of the LTC3415. For proper
measurement equipment configuration, set up the
circuit according to the diagram in Figure 1. Before
proceeding to test, make sure the jumper shunts are
in the appropriate header according to the legend in
Figure 1, except for one exception: insert jumper JP5
shunt into the off position, which connects the RUN
pin to ground (GND), and thus, shuts down the cir-
cuit.
When measuring the input or output voltage
NOTE:
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 Fig-
ure 2 for proper scope probe technique.
With the DC768 set up according to the proper
1.
measurement 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.).
should read 0V. If desired, one can measure the
shutdown supply current at this point. The supply
current will be approximately 400 uA, or less, in
shutdown.
Turn on the circuit by inserting the shunt in header
2.
JP5 into the ON position. The output voltage
should be regulating. Measure Vout - it should
measure 1.2V +/- 1.5% (1.182V to 1.218V).
15A POLYPHASE MONOLITHIC SYNCHRONOUS BUCK REGULATOR
Measure Vout; it
Vary the input voltage from 2.5V to 5.5V and adjust
3.
the load current from 0 to 15A. Vout should read
between 1.2V +/- 3% (1.164V to 1.236V).
Measure the output ripple voltage at any output
4.
current level; it usually will measure less than 20
mVAC.
Observe the voltage waveform at the switch node.
5.
Verify the switching frequency is between 1.3 MHz
and 1.7 MHz (T = 0.769 us and 0.588 us), and that
the switch node waveform is rectangular in shape.
Insert jumper JP5 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 +/- 1.5% toler-
ance under static line and load conditions, and another
+/- 1.5% tolerance under dynamic line and load condi-
tions (+/- 3% total).
TM
The Burst-Mode or pulse-skipping operation modes
of the LTC3415 can also be observed now by chang-
ing the position of the shunt in header JP7. 1 or 2
MHz operating frequencies can be activated by re-
positioning the JP6 shunt. The tables below show
the extra features, such as margining and spread
spectrum.
When finished, turn off the circuit (connecting the
RUN pin to ground) by inserting the shunt in header
JP5 into the OFF position.
2