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BQ25895: BQ25895 Query

Bino Mani
Prodigy 90 points
Part Number: BQ25895

Tool/software:

Hello Ti Support Team,


I have a query related to BQ25895. I am designing a battery operated medical device and I want to know whether BQ25895 can boost the battery voltage if external supplied isn't supplied. And what can be the boost voltage using battery?

Looking forward for a quick response.

Regards,
Bino Mani

  • 0
    TI__Mastermind 31120 points

    Hi Bino, 

    Please see my comments below. 

    Yes the BQ25895 can be configured to boost the battery voltage anytime an external supply is not connected at VBUS. The boost mode output is the PMID pin. Details on boost mode operation can be found in datasheet section 8.2.5 on page 19. 

    Boost mode output voltage is default set to 5.1V, but can be configured to a value in the range of 4.55V to 5.51V via 'BOOSTV' bits in REG0A. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 90 points

    Hello garrett,

    Just to avoid any confusion what should be the value of BOOSTV if I want 5V?

  • 0 in reply to Bino Mani
    Prodigy 90 points

    And my battery voltage range is 3.0V to 4.2V, 4000mAh

  • 0 in reply to Bino Mani
    TI__Mastermind 31120 points

    Hi Bino, 

    Due to the minimum bit set size of 64mV for the BOOSTV register setting you have the following options near 5V: 4.998V (0111b), 5.062V (1000b), 5.126V (default, 1001b). 

    The BOOSTV default setting is slightly above 5V on BQ25895 device to take into account the +/-3% voltage regulation accuracy (listed on page 9 of the datasheet 'V(otg_reg_acc)'). You are free to lower the BOOSTV setting if you believe 5.126V is too large a voltage for your end application. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 90 points

    Hello Garrett,

    Thanks for the details.

    Could you tell me the voltage support for I2C, CE, OTG, INT. I want to provide the pull up for each pin so I need to confirm the voltage range for each range.

  • 0 in reply to Bino Mani
    TI__Mastermind 31120 points

    Hi Bino, 

    The maximum allowable pullup voltage for all the pins you list is 7V. This information is stated in the Absolute Maximum Ratings table on datasheet page 6. The minimum required pullup voltage for each pin is 1.3V. This spec is 'VIH' (input high threshold)  and is shown for each pin on datasheet page 10. 

    For your reference common pullup voltages used by other customers is 1.8V or 3.3V. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 90 points

    Hello garrett,

    I have purchased BQ25895EVM from digikey. And tried supplying battery voltage(3.7V) at the J4(BAT & GND) and I am getting 5.1V at PMID voltage. BUt once I connect the load at the J2(PMID & GND), the voltage drops. I have connected load till1A. At 1A load, the voltage at PMID drops to 0V.

    COuld you help me?

    Below are the chnages I did in the EVK:
    - Remove the shunt connector from JP2 
    - Set R19 to 118.6ohm
    - Remove the shunt connector from JP4 

  • 0 in reply to Bino Mani
    TI__Mastermind 31120 points

    Hi Bino, 

    I have tested a BQ25895EVM with the same changes you list and I am able to connect a load > 1A at PMID without issue. 

    My best theory as to why boost mode is turning off is maybe your battery voltage is dropping below batlowv threshold (3V) with a load applied. Please monitor the battery voltage at TP5 on the EVM as you are increasing the PMID load. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 90 points

    Hello Garrett,


    Is there any way to set the current at PMID pin? I could get the current till 2.5A load at 5V PMID output. And I need till 3.1A.

  • 0 in reply to Bino Mani
    TI__Guru 57341 points

    Hi,

    No.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 90 points

    Hello Ning,

    Could you help me figure out what is the reason that I couldn't achieve 3.1A  at PMID pin?

    Regards,
    Bino Mani

  • 0 in reply to Bino Mani
    TI__Guru 57341 points

    Hi Bino,

    1. What are your test conditions such as VBUS (voltage at VBUS pin), IVBUS (actual OTG load), VBAT (voltage at BAT pin), IBAT, VSYS, ISYS when you try to enable OTG?

    2. What are all the register readings when you can't achieve 3.1A PMID?

    3. Are you testing with real battery or battery simulator?

    Thanks,

    Ning.