DEMO MANUAL DC1735A LTC3226EUD 2-Cell Supercap Charger With Backup PowerPath Controller DESCRIPTION Demonstration circuit DC1735A is a 2-cell supercap the supercapacitors and provides up to 2A peak output current with an adjustable output voltage. When the input charger with a backup PowerPath controller, featuring supply falls below the resistor programma-ble power-fail the LTC 3226. It includes a charge-pump supercapacitor threshold, the LTC3226 automatically enters a backup state charger with programmable output voltage, a low drop- in which the supercapacitors power the output through out regulator and a power-fail comparator for switching the LDO. The LTC3226 is available in a 16-lead, 3mm between normal and backup modes. The constant-input 3mm QFN surface mount package with an exposed pad. current supercapacitor charger is designed to charge two supercapacitors in series to a resistor programmable out- Design files for this circuit board are available at put voltage from a 2.5V to 5.3V input supply. The charger DEMO MANUAL DC1735A OPERATING PRINCIPLE tor stack. This pin is pulled to ground until the CPO pin comparator which monitors V under all operating OUT voltage rises within 7.5% of the programmed value. Once modes via the RST FB pin and reports the status via an open-drain NMPS transistor on the RST pin. At any time, the CPO pin is above this threshold, the CAPGOOD pin if V falls below 7.5% from its programmed value, it goes high impedance. The output of the PFI comparator OUT pulls the RST pin low almost instantaneously. also drives the gate of an open-drain N-channel MOSFET to report the status via the PFO pin. In normal mode the However, on the rising edge, the comparator waits 290ms PFO pin is high impedance, but in backup mode the pin after V crosses the threshold voltage before making OUT is pulled down to ground. The LTC3226 contains a RESET the RST high impedance. 6 6 C = 1.2F SC CPO C = 47F OUT 5 5 I = 2A LOAD CPO 4 4 V IN V OUT 3 3 V V IN MID 2 2 BACKUP BACKUP MODE MODE 1 1 (LDO IN (LDO IN DROPOUT) REGULATION) 1x 2x 0 0 MODE MODE R = 33.2k PROG PFO (2V/DIV) C = 1.2F SC 1 1 dc1735A F01 0 0.4 0.8 1.2 1.6 2.0 TIME (5 SECONDS/DIV) TIME (SECONDS) dc1735A F02 Figure 1. Charge Profile with Equal Value Supercapacitors Figure 2. Normal-to-Backup Mode Switchover QUICK START PROCEDURE Refer to Figure 3 for the proper measurement equipment 2. Connect the power supply to the V terminals, turn IN setup and jumper settings, and follow the procedure below. the power supply on, and increase the voltage to 2V while monitoring the input current. If the input current NOTE. When measuring the input or output voltage ripple, is less than 5mA, increase the voltage until the point at care must be taken to avoid a long ground lead on the which PFO goes high. Verify that V is between 3.53V IN oscilloscope probe. Measure the input or output voltage and 3.65V, the input current is approximately 320mA, ripple by touching the probe tip directly across the V IN the output voltage is approximately equal to the input or V and GND terminals. See Figure 4 for the proper OUT voltage and the voltage on the CPO pin is rising. scope probe technique. 3. Monitor the voltage on CPO and CAPGOOD. Verify that 1. Initial jumper, power supply and load settings: CAPGOOD goes high when CPO is at 4.6V and that CPO JP1 = EN Power Supply = OFF charges between 4.83V and 5.23V. Verify that V is MID JP2 = 110mA Load = Off one-half of CPO. Verify that RST is high. JP3 = 110mA Pulse Generator = OFF dc1735Af 2 VOLTAGE (V) 1V/DIV VOLTAGE (V)