DC1887A Analog Devices

DEMO MANUAL DC1887A LTC3128 High Efficiency 2-Cell Supercapacitor Charger and Balancer Converter Description Demonstration circuit 1887 is a DC/DC supercapacitor The DC1887 has a small circuit footprint. It is a high per- buck-boost charger and balancer converter featuring the formance and cost effective solution for charging and LTC 3128. The DC1887A operates over 1.72V to 5.5V input balancing supercapacitors. Please read the LTC3128 data and charges the output up to 5.5V. Also, the LTC3128 has sheet along with this manual. 2% precision input current limit, which allows the circuit to Design files for this circuit board are available at operate effectively with current limited input power sources DEMO MANUAL DC1887A Quick s p D Demonstration circuit 1887 is easy to set up to evaluate NOTE: Make sure that the input voltage V does not IN the performance of the LTC3128. For proper measure- exceed 5.5V. ment equipment setup refer to Figure 1 and follow the 4. Set the input voltage to 3.3V and check for the proper procedure below: output voltage of 4.2V. If there is no output, temporarily NOTE: When measuring the input or output voltage disconnect the load to make sure that the load is not ripple, care must be taken to minimize the length of set too high. oscilloscope probe ground lead. Measure the input 5. Once the proper output voltage is established, adjust the or output voltage ripple by connecting the probe tip load and observe the output voltage regulation, ripple directly across the VIN or VOUT and GND terminals as voltage, efficiency and other parameters. shown in Figure 2. 6. Note that the output voltage V will vary with load. OUT 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. + C OUT The LTC3128 circuit maximizes the output current while V GND OUT keeping the input current within the preset current limit. Figure 2. Measuring Input or Output Ripple This keeps the supercapacitor charging time to a minimum. 1. With power off, connect the input power supply to V IN CHANGING THE OUTPUT VOLTAGE and GND. To change the output voltage from the programmed 4.2V, 2. Keep the load set to 0A or disconnected. change the voltage divider resistors connected to the 3. Turn the input power source on and slowly increase the LTC3128 FB pin (see the schematic on page 5). input voltage. Be careful not to exceed 5.5V. Figure 1. Proper Measurement Equipment Setup dc1887af 2 ure roce tart