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Original question:

BQ25798: Not able to charge battery beyond 4A

BQ25798: Not able to charge battery from 2nd input.

Iz Olmez
Prodigy 90 points
Part Number: BQ25798
Other Parts Discussed in Thread: TPS25751,

Tool/software:

Hi,

I have previously communicated with Christopher Lim on this subject:

Using the evaluation module, I have not been able to charge beyond 4 A. We had a separate discussion about that earlier.

I now have my own design with TPS25751 for USB-C front-end, and a 2nd 20VDC input switched into the VBUS input of the charger by two external back-to back MOSFET circuits (excerpt below)

I am able to write the configuration file that I generate using the online config tool, into the EEPROM and able to negotiate 20V from USB-C, charger switches to the USB input  and charge up to 4A with USB-C port connected (PPHV above)

When the 2nd input is connected (UAI-20V above) only, meaning USB-C input is disconnected, charger switches to the 2nd input. ACDRV2 asserted, MOSFET is switched, I measure 20V at VBUS input pins. Good.

BUT charger never comes ON!  What am I missing? Is the charger not supposed to charge from the 2nd input? I do not se any mention of that on the data sheet.

Thank you,

_Iz

  • 0
    TI__Guru**** 171246 points

    Hi LZ,

    The TPS25751 firmware sets the charger's EN_CHG bit = 0 if no USB-C port is connected.  TI's power interface team is working on a fix for the firmware. I will move this post to them.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 90 points

    Hi Jeff,

    Thank you for the reply. When can I have my hands on this new firmware? OR, how can I set this bit myself?

    Actually, it would be good to learn how to set particular bits using the I2C tool. I am using Aardwark TotalPhase Flash Center tool to program the flash, but I also have Control Center tool.

    Thank you,

    Iz

  • 0 in reply to Iz Olmez
    TI__Guru**** 171246 points

    Hi LZ,

    Your EP can I2C write a 1 to REG0x0F[5] to the charger at 0x6B in order to enable charge.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Mastermind 32252 points

    Hi LZ, 

    The TPS25751 integrated I2C control is optimized for a single-input use-case with BQ25798. Therefore, when the USB-C cable is disconnected, the PD sets the BQ to a safe state and disables charging. 

    The TPS25751 supports I2C passthrough where it will write to the BQ through the PD I2Cc interface via a 4CC command 'I2Cw'

    Please let me know if you have additional questions/concerns. 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 90 points

    Hi Jeff,

    I have played with writing the EN_CHG bit and was able to charge from input 2, but it reverts back to =0 if I switch inputs. I want to be able to charge using either input, regardless of which one plugged in first.

    You mentioned initially that:

    "The TPS25751 firmware sets the charger's EN_CHG bit = 0 if no USB-C port is connected.  TI's power interface team is working on a fix for the firmware"

    I need this bit to stay EN_CHG=1 in either case, when input 1 is plugged in, or when input 2 is plugged in, so that I can charge from either port. 

    Since I cannot make the bit file using the online config tool with this EN_CHG bit always asserted, could you please make me a bit file for CAT24C512 (see my earlier schematic) with these parameters:

    USB-PD= sink, 20V, 100W

    charge current limit=5A

    charge termination current= no preference

    pre- charge current= no preference

    charge voltage = 14.6V

    EN_CHG=1 on either VAC1 or VAC2 present.

    Thank you,

    Iz

  • 0 in reply to Iz Olmez
    TI__Mastermind 32252 points

    Hi LZ, 

    Unfortunately, we currently do not have an optimized solution that is suitable for dual-inputs. The TPS25751 integrated I2C control is optimized for a single USB-C input to BQ. 

    For applications with PD+BQ with dual-inputs, we highly recommend the MCU control the BQ for a more simple/efficient solution. 

    Please let me know if you have additional questions/concerns. 

    Best Regards, 

    Aya Khedr