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BQ25060: behavior when battery is not connected

li tony
Prodigy 10 points
Part Number: BQ25060
Other Parts Discussed in Thread: CSD25484F4

Hi team,

In our design, We are using bq25060 in power path mode. This is our schematic.

If the battery is NOT connected, after the first time apply 5v on the IN pin, the voltage on OUT and BGATE pin are close to 5v and the BAT pin voltage is 0 volte. But when we remove the power supply and apply it again, the  OUT and BAT pin voltage is about 4.2v. At the same time, we observe a 10hz square wave on the BGATE pin with an amplitude of 4.2v.

 is this the expected behavior of bq25060? Why do we see the 4.2v on the BAT pin only when we remove and apply the power again?

thanks 

Tony

  • 0
    TI__Mastermind 23410 points

    Hi Tony,

    It sounds like the device could be charging the capacitors on BAT since that can act as very small battery. Would you be able to share waveforms of the VBAT for these two situations? Are you discharging the BAT pin before inserting the power supply and seeing the 10 Hz square wave? 

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    Hi Anthony,

    Thanks for your reply. 

    If the battery is not connected, during the first power cycle, the VBAT is always 0v. 

    When I saw the 10hz square wave, I did not discharge any pin of the bq25060. Your reply makes sense, it looks like the IC charging the capacitor on VBAT when I apply the power supply the second time. Here is the waveform of the VBAT.

    Before I apply the 5v on the IN pin, discharging the BAT pin doesn't change the behavior, the VBAT and VOUT become 4.2v. 

    BUT, if i discharge the OUT pin, before applying 5V, the voltage on OUT and BGATE is always close to 5V.  And the VBAT is very close to zero.



    Is this the normal behavior/voltage of BQ25060? But if the VBAT is always zero, it can not wake up a fully empty battery(high Z mode).

    thanks

  • 0 in reply to li tony
    Prodigy 10 points

    Here is the waveform of BGATE when I apply 5v on the IN pin for the first time. I can see a small pulse of 2ms. I think this corresponds to what the datasheet said “The device sources a small current out of BGATE for 2ms and monitors the voltage.”. but the voltage is too low, only 0.7v. and then BGATE remains 5V.

    without discharging any pin, if I apply the 5v on the IN pin. The waveform is shown below, there is still a small 2ms pulse, the voltage is about 1.2v. but it is still lower then logical high of the device.

    The BGATE is connected to the gate of p mosfet CSD25484F4. Does the BGATE level correct?

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    Hi Anthony,

    We tested the BQ25060 with another P MOSFET TSM2301ACX RFG. the waveform is different with those using CSD25484F4 mosfet.

    Using TSM2301ACX , the BGATE waveform looks like :

    the 2ms pulse is about 5v. and we got voltage on BAT pin.

     

    Does the mosfet selection affect the functionality of BQ25060?

    thanks for you help

  • 0 in reply to li tony
    TI__Mastermind 23410 points

    Hi Li,

    Apologies for the delay.

    The BQ25060 looks to be working as intended but the as the CSD25484F4 does not have enough voltage on GATE pin, it is not able to open the FET completely. The TSM2301ACX  doesn't appear to have that behavior here. I'd have to look at the datasheets to be sure but it is most likely related to the FET. 

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 10 points

    Thanks for your reply. 

    This is also what we are suspecting. If the problem is related to the FET, could you give us some suggestions? What would be the technical specification of the FET?

    Best regards

    Tony

  • 0 in reply to li tony
    TI__Mastermind 23410 points

    Hi Tony,

    I'm currently out of office. I recommend the FET that we use on the EVM (NTR4101PT1G) or similar. I'll be able to look through the differences when I return to the office in a week. I appreciate your patience.

    Best Regards,

    Anthony Pham