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BQ25895: Review design buck/boost charging using BQ25895RTWR

Travis
Prodigy 10 points
Part Number: BQ25895

Tool/software:

Hi

I am new to circuit design so I am unsure of my circuit using BQ25895RTWR especially in regards to buck/boost for circuit power and charging.

Can anyone please confirm I am on the correct path attached is SCH.

Thank you. SCH_Sender_2024-06-11-2.pdf

  • 0
    TI__Mastermind 31100 points

    Hi Travis,

    Thank you for reaching out via E2E. Please see my comments below on schematic review. 

    - BTST capacitor (C40 in your schematic) must be 47nF as mentioned in the pin functions table in the BQ25895 datasheet. 

    -If DSEL pin function is not to be used please leave it floating. In your current schematic you have it connected to GND via a 0ohm resistor. 

    -PMID pin should not be connected to same node as SW pin and inductor. The only component or pin which should be connected to the node from SW to the inductor is the capacitor from BTST to SW. 

    -You appear to be missing a resistor in parallel to the NTC connected from TS to GND. Figure 8-6 on datasheet page 23 illustrates the required circuit at TS pin. Additionally, the 100nF cap C41 is not needed at TS pin. 

    All other connections related to the BQ25895 device look good. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 10 points

    Thank you for your help much appreciated.

  • 0 in reply to Garrett Kreger
    Prodigy 10 points

    Hi Garrett,

    Please see attached I have made changes you suggested. Still not 100% sure on the PMID pin and if I have done it correctly now.

    SCH_Sender_1_2024-06-12.pdf

  • +1 in reply to Travis
    TI__Mastermind 31100 points

    Hi Travis, 

    I have reviewed the updated schematic and it mostly looks good. Regarding the PMID pin it is now correctly connected to just a capacitor to GND, but C35 and C34 can be removed from the node connected to SW pin. 

    With those two capacitors removed the BQ25895 portion of your schematic looks good. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 10 points

    Hi Garret,

    Thank you for you previous help I have received the sample PCB and everything is working as expected except I have one issue.

    When powering from off with the battery the BQ25895RTWR is not starting switching I was getting 0.5V then randomly jump up to 1V. If power from USB no problem or if leave battery connected then unplug USB no problem.

    But just as I was writing this and was going to test with scope it has started working! I thought it may have been the WAKE so I had removed R11 (was there for this purpose) and it did not work. But just now it is powering up from off with battery no problems.

    Just wondering what could of been causing this issue was it the ship mode? or any other idea as not sure if intermittent fault.

    Once again thank you for your help I appreciate it. SCH_Sender_6_2024-07-04.pdf

  • 0 in reply to Travis
    TI__Guru 57331 points

    Hi,

    We will check and get back to you soon.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    TI__Mastermind 31100 points

    Hi Travis, 

    Thank you for your patience. Please see my comments below. 

    Travis said:
    BQ25895RTWR is not starting switching I was getting 0.5V then randomly jump up to 1V.

    Where are you measuring 0.5V,1V? PMID or SYS? 

    If you were in ship mode you would not see battery voltage at any output pin. 

    Best Regards,

    Garrett