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dc1887af

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.

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. Oncetheproperoutputvoltageisestablished,adjustthe

load and observe the output voltage regulation, ripple

voltage, efficiency and other parameters.

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.

Thiskeepsthesupercapacitorchargingtimetoaminimum.

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).

Figure 2. Measuring Input or Output Ripple

Figure 1. Proper Measurement Equipment Setup

+

–

GND

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.