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BQ25895: Enquiry on BQ25895 connection

Poh Kok Keng
Genius 5512 points
Part Number: BQ25895

Dear Sir/Madam,

I am using BQ25895 is standalone mode without boost with power adaptor input 4 to 12V. Output is connected to a li-ion battery with 1S4P expected 3V to 4.2V.

Can I confirm the following:

1. if boost mode is not using, can I put OTG pin floating? is it an issue?

2. Can I leave QON floating?

3. On my board, I measure the TS is 3V, does this means I do not need to connect the thermistor between TS->GND pin? can I ignored the thermistor to save cost?

 I am facing intermittent battery does not start charging issue. Even after disconnecting and reconnecting the DC adapter, battery charging still does not start.

Do you have any troubleshooting guide to follow?

I have the schematic with me but it is private. Do let me know if I can send the schematic to you to check on the connection.

Best Regards,

kpk

  • 0
    TI__Expert 8230 points

    Hello kpk,

    See my comments below:

    • If boost mode is not used, OTG pin should be pulled high with a 10k Ohm resistor to ensure a fixed logic state at all times on the pin.
    • QON can be left floating as it has an internal pull down.
    • The thermistor can be omitted from the design to save cost, but a resistor network to fix the TS pin voltage should be used. Typically we recommend customers to use the following resistor network to fix the TS pin at a voltage corresponding at a normal charging temperature.

    Regarding the intermittent charging, what are the test conditions during this behavior? 

    Could you monitor the TS pin to verify the voltage is not fluctuating in and out of Hot/Cold window, disabling and enabling charging?

    Regarding the schematic, you can begin checking your schematic by comparing it with the bq25895 EVM schematic. You can also send me the schematic privately for further review.

    Hope this helps.

  • 0 in reply to Fernando Lopez
    Genius 5512 points
    Dear Sir,

    1. If OTG pin pull high, this will enabled boost mode right? Should we pull this to LOW instead?
    I already sent the schematic to you privately. thx

    Best Regards,
    kpk
  • 0 in reply to Poh Kok Keng
    TI__Expert 8230 points
    Hello kpk,

    Yes, OTG should be pulled low if not being used, sorry for the confusion.

    Thank you for the schematic, I will provide my comments regarding it shortly.