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TPS61253: 375mAH battery -TPS61253 - BQ25895 chip - load circuit does not boot up

Aniket Jangam
Prodigy 10 points
Part Number: TPS61253
Other Parts Discussed in Thread: BQ25895, ,

Hello all,
I am using TPS61253 Boost IC to boost 3.8V from 375mAH Li-Ion battery to operate a load of 2A and also charge the backup Li-Ion battery of 115mAH using BQ25895 chip. Looks like battery is not able to deliver the necessary current and the load circuit does not boot up correctly. Is there a way to fix this issue?
If I use an external supply at 4.7V and 3A. the complete circuit works, charges the backup battery and is stable. So I am guessing the issue is the current limitation from the 375mAH battery.
Appreciate if anyone could guide me to the correct way of doing this.

Regards,
AJ

  • 0
    TI__Mastermind 34201 points

    Hello AJ,

    Have you ever test the TPS61253A device output voltage? Is the device switching?

    Please share the schematic and layout so that I can check if the issue is related to that. Thank you.

  • 0 in reply to Zack Liu
    Prodigy 10 points

    Hello Zack,
    since the current limit of the TPS61253A is upto 1.5A and there is an inbuilt Booster in the BQ25895, I am thinking to get rid of the TPS61253A. But I am having issues with getting the BQ25895 boost circuit going when the load is attached. The boosting works only when there is no load. As soon as I connect the load, the voltage drops around 2.5V. I read in the forums that this might be due to the "resistive connection to the VBAT pin", so as to avoid that I soldered a wire right on the VBATT pin of the component, but still the drop to 2.5V exists. 
    I do not need the 3.1A completely, so I do not have a diode in between SW and the PMID pin. I have a 47uF cap on the PMID pin, which I think should be enough to handle the 2.4A output to the load.

    Could you let me know what is happening here?

  • 0 in reply to Aniket Jangam
    TI__Mastermind 34201 points

    Hello AJ,

    I'm the applications engineer that supports the boost device TPS61253A. So I'm not familiar with the BQ charger device.

    I'm very glad to debug the boost converter with you if you can share the schematic and layout.

  • 0 in reply to Aniket Jangam
    TI__Guru** 103175 points

    Hello AJ,

    As Zack mentioned, the schematic will help us understand your system better and allow us to give more suggestions. The bq25895 does have a boost feature to supply 5V at the PMID node for OTG functionality, but it cannot take a low input voltage on VBUS and boost it to charge the battery. There is also a delay to switch from charge to the OTG, it is not a seamless switchover.

    The bq25895 charger can boost from the BAT to PMID, or it can charge from VBUS to BAT, but it cannot do both at the same time.

    Sincerely,

    Wyatt Keller