Hello,
A TPS61260EVM-673 is used in order to evaluate the TPS61260 as a supercapacitor charger.
Output voltage was set a 4.0V with R2=143K instead of 182K.
Output current limit was set at 30mA with R3=6.8K instead of 2.0K.
The supercapacitor is formed with two CAP-XX HW203 (0.55F/90mOhm) in parallel (with 47K balancing resistors to VOUT and GND).
Voltage source is a primary lithium element (SAFT LS14500 3.6V with 50mA continuous max current).
VOUT is used to power a radio board (pulsed load 1A/400ms, 50s period)
The first day of evaluation the board was tested with good results so behavior and voltage values was exactly the same as computed previously.
24 hours later we measured the output voltage without powering the board. VOUT was 1.2V, corresponding to the voltage discharge in the balancing resistors. After connecting the voltage source we saw that the TPS61260 wasn't switching so the voltage remained constant.
After disconnecting the input source and discharging the output capacitor the voltage source was connected again and then VOUT rise and stabilize to 0.5V (Device Vref internal value is 500mV so TPS61260 behavior corresponding to VOUT directly connected to FB pin).
When I measure the middle node of the feedback resistor network R1/R2, the voltage is close to 0V but the ground resistor is not failed.
It seems that the TPS61260 is not anymore functional but i was not able to find in the datasheet a violating of any Absolute Maximum Rating.
The Supercap value is 1.1F so the device will support a extended period of time with VOUT>>VIN when the input source is disconnected but i suppose that a step-up regulator is designed to support this kind of situation.
Is anyone have an idea to explain the failure of the TPS61260?
Thanks and best regards