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BQ25601RTWT

Habib Mousavizadeh
Prodigy 30 points
Other Parts Discussed in Thread: BQ25601, BQ2560, TPS22975

Hi,

There is an issue with the bq25601 on battery connection. We are using a single cell Li-Ion 3.7V battery connected to the BAT pin. The BATFET turns ON and the voltage appears on SYS pin but when it connects to the load the BATFET gets OFF and drops the voltage. However when I use the longer wire for my battery connector, it works fine. Wondering what is the issue?

  • 0
    TI__Genius 11850 points
    Hi Habib,

    Can you give me some more information about your test setup? Are the battery and the load the only things connected to the board?

    If possible, a waveform showing VBAT, IBAT, VSYS, and ISYS when you connect the load for both cases (incorrect behavior and correct behavior with the longer wire) would be very helpful.

    Also, is the BATFET_DIS bit being set and latching the BATFET off?

    Best regards,
    Angelo
  • 0 in reply to Angelo Zhang87
    Prodigy 80 points

    Hi Angelo,

    Here is the simplified block diagram: Looks like the BATFET of bq2560 tripping is due to the high inrush current. The rise time of the Load Switch is not high enough.

    Regards,

    Habib

  • 0 in reply to HABIB MOUSAVIZADEH
    TI__Genius 11850 points
    Hi Habib,

    Your attachment isn't showing up for me.

    Based on your description though, it sounds like Section 8.3.2 of the datasheet. When you connect the load, the discharge current through the BATFET is too high, so the BQ25601 turns off the BATFET, causing your VSYS to drop. If the BATFET_DIS bit is being set, then that would confirm our suspicions.

    Best regards,
    Angelo
  • 0 in reply to Angelo Zhang87
    Prodigy 80 points
    Hi Angelo, yes that is what happens and confirmed. Now we are looking at the best solution to prevent this from happening. Adding TPS22975 load switch with configurable rise time sounds is good solution. Any thought?
  • 0 in reply to HABIB MOUSAVIZADEH
    TI__Genius 11850 points
    Hi Habib,

    I agree; adding a load switch with a configurable rise time sounds like a good solution to decrease the discharge current through the BATFET. Sections 10.2.2 and 10.2.3 of the TPS22975 datasheet discuss how to choose an appropriate capacitor value to limit inrush current. This application report may also be helpful to you: www.ti.com/.../slva670a.pdf

    Best regards,
    Angelo
  • 0 in reply to Angelo Zhang87
    Prodigy 80 points

    Hi, Angelo,

    Thanks for your confirming this. However there is still one thing I'd like to get your thought on it. It is related to the section of 10.1.2 and 10.1.3 of the same data sheet on selecting the Cin and CL.

    Since our CL is too big (~2mF), I am wondering what would be the size of the Cin? the data sheet says it should be 10 times of the CL. Although the Cin is optional but CL can not be optional and it comes from my circuit's load capacitance. So how do you explain this? Do we really need such a big cap for Cin, in my case 20mF!!!

    Regards,

    Habib

  • 0 in reply to HABIB MOUSAVIZADEH
    TI__Genius 11850 points
    Hi Habib,

    Sorry, I'm not sure about this because I only support battery charger ICs. Please create a new thread asking about the TPS22975 and the appropriate team within TI will get back to you.

    Best regards,
    Angelo