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BQ24170

Grant Downie
Prodigy 155 points
Other Parts Discussed in Thread: BQ24170

Hi,

I am using the BQ24170 with 12V input and 2-cell battery almost identical with the schematic (Same FETs, Diodes with a few resistor changes for charge current) and layout in SLUU463 "bq24170EVM". I have noticed that ACDRV is continuously turning on then off. The Same behavior is observed on BATDRV. I am checking all loaded parts on the board but if anyone has any ideas on how to narrow down the source of the problem that would be very helpfull. VREF is 3.3V and OVPSET is 1.2V. I have isolated the load and disconnected the battery however the behavior is the same.

Regards Grant

  • 0
    Prodigy 155 points

    Hi,

    A quick update. All parts have been checked and looks good.

    REGN is 6V and can be disabled by taking ISET pin to GND via FET same as EVM.

    If there is no battery connected and 12V input is connected the battery detection logic seems to think that the battery is connected and trys to charge. ACDRV is being turned on and off, same for BATDRV,

    If there is a battery connected and 12V input is connected the battery starts to charge. The charge current ramps up quicklt to 2A and continues until a component (not known) starts to smoke.

    Output capacitance on VBAT is 21uF.

    My question is what can cause cause false battery detection and charge current to continue to increase? 

    Regards Grant

  • 0 in reply to Grant Downie
    Prodigy 155 points

    Hi,

    Interestingly.

    If there is no battery connected and 12V input is connected the battery detection logic seems to think that the battery is connected and trys to charge. ACDRV is being turned on and off, same for BATDRV.

    If you start to wind the 12V input down close to the 2-cell regulation voltage you see ACDRV being turn on "high" and BATDRV being turned off "high". Winding the input back up exhinits the same ACDRV/BADRV off an don behavior.

    There is one exception to my layout and that is that i have used a common ground. That is the BQ24170 components are on top L1 and bottom L10 along with traces and reference planes "GND on L2 and L7. Other signals are on L3 and L6. L4 and L5 is VCC and GND. It is difficult to maintain a reference plane for signals if i have to cut up L2 and L7 to isolate AGND from DGND. 

    Regards Grant

  • 0 in reply to Grant Downie
    TI__Mastermind 31120 points

    I would use a EVM to see how your application works.

    For your circuit, I would monitor the input voltage and battery voltage and AVCC pin to see if the part is going into sleep mode or UVLO mode.

  • 0 in reply to Charles Mauney
    Prodigy 155 points

    Hi,

    I found that the PMOS pulldown resistor on the gate was too low. Removing allowed correct operation. 

    Regards Grant