DEMO MANUAL DC2040A
LTC3355EUF
20V 1A Buck DC/DC with
Integrated SCAP Charger
and Backup Regulator
DESCRIPTION
Demonstration circuit 2040A is a 12V to 4V/1A regulator a 3F supercapacitor can provide a 4W output when the
with an integrated supercap charger and backup boost input power fails (~600ms).
regulator featuring the LTC 3355EUF. The LTC3355
Design files for this circuit board are available at
charges up a 3F supercapacitor from the output when the
DEMO MANUAL DC2040A
QUICK START PROCEDURE
Note: Without an external supply used for the LED pull-up
Refer to Figure 3 for the proper measurement equipment
power, PS2, the CPGOOD, RSTB, or PFOB LEDs will not
setup and jumper settings and follow the procedure below.
illuminate until VOUT has enough voltage.
Note: When measuring the input or output voltage ripple,
4. Set LD1 to 1A. Observe the voltage on VOUT.
care must be taken to avoid a long ground lead on the
oscilloscope probe. Measure the input or output voltage
5. With an oscilloscope, connect one probe to the PFOB
ripple by touching the probe tip directly across the VIN,
terminal with the vertical scale set to 2V/Div. Set another
VCAP, or VOUTx and GND terminals. See Figure 4 for
probe to the VOUT terminal with the vertical scale set
proper scope probe technique.
to 1V/Div and set a third probe on the VCAP terminal
with the scale set to 1V/Div.
1. Make sure the following jumpers are set as described
below:
6. Set the horizontal scale to 100ms/Div and set the
oscilloscope to trigger on the falling edge of PFOB in
MODE jumper, JP1, to the BURST position;
Normal trigger mode.
EN CHARGER jumper, JP2, to the EN position;
7. Turn off PS1 and observe how long the output is
PULL-UP PWR jumper, JP3, to the VOUT position.
maintained with 4W of power. Compare the results to
2. Set PS1 to 0V and LD1 = 0A.
Figure2.
3. Slowly increase PS1 until VIN is equal to 12V. Observe
8. The VOUT and VCAP voltages, the input current limit,
the voltage on VOUT and VCAP. The CPGOOD LED
charge current and boost peak current can all be re-
extinguishes as the VCAP voltage approaches the set
programmed via resistors. Please refer to the LTC3355
float voltage.
data sheet for more details.
Figure 3. Proper Measurement Equipment Setup for DC1468A
dc2040af
2