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BQ25892: Charging does not stop at termination current when system is switched on

Paul Zimmer
Prodigy 10 points
Part Number: BQ25892
Other Parts Discussed in Thread: BQ27426,

Tool/software:

We are using the BQ25892 in combination with the BQ27426 Fuel Gauge to charge out LiPo battery. When the whole system is switched off, the charging stops at the specified 

  • ti,termination-current = <50000>;

 

means 50mA. When the system is switched on, it is charged until "infinity" - means the charging current in CV phase is dropping below these 50mA. As far as I could test it, the charging current goes down to 0.009 mA and there I stopped. 

For me it seems, that it is somehow comparing the overall incomming system current with the termination-current. This would mean that:

  • (Charging Current + System Current) > 50mA --> charging is not stopped. 

Do you know this behaviour? Or do you see a problem in the wiring, when focusing on the path from VBUS (USB-C charging cable) to VBAT_Fuel on the BAT pins to the Battery connector? 

Any idea or help is highly appreciated, as I am in a complete dead end of my investigations. 

 

  • 0
    TI__Mastermind 31140 points

    Hi Paul, 

    Thank you for reaching out via E2E. 

    Firstly, the minimum allowable termination current threshold on the BQ25892 is 64mA. This is stated on page 41 of the datasheet in table 9-14 which outlines the ITERM register setting.  Can you please help to confirm whether ITERM is indeed set to 0000b (64mA)? 

    The BQ25892 is designed such that battery charging can terminate while there is still significant system current draw. Charge current + system current > 50mA should not be the cause for a lack of termination. 

    If possible can you provide a waveform of VBAT and charge current with the device approaching termination threshold? It would also be helpful to review a register dump from BQ25892 with the device in CV phase to verify there is not a condition/fault which would be preventing termination. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 10 points

    Hi Garrett, 

    Thank you very much for your answer. 

    This helped me digging deeper in the registers of our charger. There I found that the I ICHGR current is just too high and additionally reactive to the current that is drawn from parts of the system. 

    In the end it turned out that we have mistakenly one komponent still hanging on the VBAT_Fuel line and therefore it could have never worked. 

    Thank you for pushing me into the right direction on this. 

    Best, 

    Paul