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BQ25170: Device turns on and off while charging battery.

Josh Laube
Prodigy 10 points
Part Number: BQ25170

Tool/software:

I have a design for BQ25170 that is almost identical to the application note for charging a single cell Li-po battery but when supplied with 5V for VIN the chip appears to turn on and off at a period of around 2 seconds. I have populated only the schematic seen below on a board and the problem still persists. The battery connected at VBAT is 1200mAh though I have also tried a 2200mAh one with the same results. Given enough time the battery will eventually charge up through the sequence of short pulses but it takes much longer than it should and the STAT pin turns on and off with the charger. When the battery voltage gets around 4V it does go into a continuous charge mode per the datasheet. What needs to be tweaked to get this to work without pulsing when the battery voltage is from 3.4 to 4 V?

Here is what it looks like with the oscilloscope measuring VBAT:

And here is the board layout:

  • 0
    TI__Guru 69441 points

    Hello

    The schematic and layout look OK.

    2 seconds is a time used by the TS pin / NTC.   What voltage are you seeing on the TS pin should be about 0.380mV?

  • 0 in reply to Bill Johns
    Prodigy 10 points

    The voltage at the TS pin measured around 200mV when the thermistor was on the board, I assume you mean it should be around 380mV? The resistance I am measuring across RT1 is 9 kOhm at room temp so it seems odd that that would cause the issue.

    I took off the thermistor and replaced it with a 10k resistor and powered up the board again, the TS pin is now sitting at 378mV and battery is charge is behaving as expected so it must be some issue with the thermistor. Since the design doesn't really need to check the battery temperature I will stick with the 10k resistor for now.

    Thank you!