Quick Start Procedure; Changing The Output Voltage - Linear Technology DC1887A Demo Manual

DEMO MANUAL DC1887A

Quick start proceDure

Demonstration circuit 1887 is easy to set up to evaluate
the performance of the LTC3128. For proper measure-
ment equipment setup refer to Figure 1 and follow the
procedure below:
NOTE: When measuring the input or output voltage
ripple, care must be taken to minimize the length of
oscilloscope probe ground lead. Measure the input
or output voltage ripple by connecting the probe tip
directly across the VIN or VOUT and GND terminals as
shown in Figure 2.
Figure 2. Measuring Input or Output Ripple
1. With power off, connect the input power supply to V
and GND.
2. Keep the load set to 0A or disconnected.
3. Turn the input power source on and slowly increase the
input voltage. Be careful not to exceed 5.5V.
2
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C
OUT
V GND
OUT
Figure 1. Proper Measurement Equipment Setup
NOTE: Make sure that the input voltage V
exceed 5.5V.
4. Set the input voltage to 3.3V and check for the proper
output voltage of 4.2V. If there is no output, temporarily
disconnect the load to make sure that the load is not
set too high.
5. Once the proper output voltage is established, adjust the
load and observe the output voltage regulation, ripple
voltage, efficiency and other parameters.
6. Note that the output voltage V
This is due to the current source nature of the LTC3128
power converter. As the output voltage increases the
output current will decrease in order to maintain the
input current below the preset limit.
The LTC3128 circuit maximizes the output current while
keeping the input current within the preset current limit.
This keeps the supercapacitor charging time to a minimum.
IN

CHANGING THE OUTPUT VOLTAGE

To change the output voltage from the programmed 4.2V,
change the voltage divider resistors connected to the
LTC3128 FB pin (see the schematic on page 5).
does not
IN
will vary with load.
OUT
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