Other Parts Discussed in Thread: TPS629210
For an application, I am using TPS61094 in auto buck or boost mode having a supercap (1F, 3V ) as buck up power. I have set charging termination voltage to 2.5V and charging current to 10mA. I have also set the regulated output when in boost mode to 3.3V. This is the circuit I am using:
Everything works as expected so I added a small load (3-5mA) to the output for some longer term test. The load was driven from the 3.5V input so we never extract energy from the backup supply (super cap).
After some time (~4 hours later) I observed that the Voltage at SUP+ exceeded the termination voltage that I have set. I am using a scope and I am measuring 2.46V when the super cap stops charging. After 5 hours I am measuring 2.58V and after 7 hours I am measuring 2.64V.
Do you have any clue what condition might cause this behavior. I had the feeling that in this case the super cap will discharge because of the leakage current for 100mV below the set termination voltage and then charge back again to 2.46 volts. I can not understand how it is possible to go above the set termination voltage.
Thank you in advance!