bq2002T Fast Charge Management IC: Fast charge times out & goes to the top-off mode in less than one minute (about 55 seconds). If I momentarily disconnect and reconnect the charger input it charges for another 55 seconds and then again goes to top-off. The 55 second time is quite repeatable.
The measured voltage at the TM (timer mode select) pin is 2.41V when the measured supply (Vcc) is 5.09V, so the fast charge should last 320 minutes.
The measured TS (temperature sensor) voltage is 1.68V and does not change significantly, so it is not near the high or low cut-off values. The thermistor circuit is similar to the DV2002 evaluation board and includes a 100Kohm/0.027ufd filter on the TS pin.
The BATT pin measured voltage is typically around 1.3 volts, well short of the 2V cut-off value.
The circuit uses a 2N3904 to control an LM317 regulator (set up as a constant current source) in a circuit similar to the DV2002 board.
I have isolated the charger/battery circuit from all other circuitry on my board, so nothing else is powered, drawing current or generating electrical noise. I am charging three 1.2V NiMH AA cells in series.
I have run this test on two different circuit boards (two different bq2002T ICs) with the same result.
Does anyone have suggestions or have had a similar experience? (I did see one somewhat-similar post already in this forum, although in that post the cut-off time was less than an hour rather than less than a minute.)
Thank you.