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BQ25890: Disable HV charging - Keep Max 5V from charger

Disco Inferno
Prodigy 90 points
Part Number: BQ25890
Other Parts Discussed in Thread: , BQ25895M

Hello,

I have a device that uses the BQ25890 charger chip.
The chip is connected to a USB C connector (D+/D- only) on the PCB.
The problem is that the charger is delivering 9V to the charger chip, I suppose this is because the chip and charger did a handshake and agreed on a high voltage.
I need the voltage to not go above 5.0-5.5 Volts.
The current should ideally be ~1050mA, but if it is restricted to 500mA that is also ok.
I have tried to restrict and disable the handshake, the MaxC and HV functions, but no matter what I do, the charger always delivers 9V to the device.
- Can you please explain how I can achieve this, how to disable the handshake and get the charger to default to maximum 5V?
- if this is not achievable, then can you please let me know if this is this achievable with the BQ25890H variant (keeping the current high and voltage to 5.0V maximum)?
Thanks kindly in advance for your reply and help.
Stuart
  • 0
    TI__Mastermind 24555 points

    Hi Stuart, 

    Thank you for reaching out via E2E. On the BQ25890 and BQ25890H HVDCP and MaxCharge functions need to be disabled in REG02 before the USB input is connected to prevent the charger IC from performing a handshake and negotiating to 9V. Therefore to ensure the device never operated with 9V input you would need to modify bits 2 and 3 in REG02 when being powered from the battery only because these functions are default enabled. 

    To simplify your design you will ideally want these bits in REG02 to be default set to disabled state. This is the case on the BQ25895M device, which is an IC from the same product family and has the same pin out as the BQ25890. 

    Please let me know if you have any additional questions. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 90 points

    Hi Garrett,

    This is what I tried to do but to no avail. Setting Reg02 to value 0X40 produces the same result. The battery is always connected and I remove and replace the USB cable. before and after programming, to check.

  • 0
    Prodigy 90 points

    To confirm the theory of operation: If I disable the HVEN and MaxC bits then it should never negotiate anything above 5V? Or do I need to disable the handshake process entirely?

  • 0 in reply to Disco Inferno
    TI__Mastermind 24555 points

    Hi Stuart, 

    Disco Inferno said:
    To confirm the theory of operation: If I disable the HVEN and MaxC bits then it should never negotiate anything above 5V?

    This is correct. With those two bits set to disabled state the BQ25890 will not attempt to negotiate a voltage above 5V. You do not need to disable the handshake process entirely.

    Referring to the figure included below taken from page 17 of the BQ25890H datasheet you can see that disabling MaxCharge and HVDCP will remove the adjustable high voltage adapter handshake block from the detection scheme. The D+/D- detection will still work to detect and set different current limits without requesting a voltage increase. 

    I also have a few questions regarding the testing you are performing to help with debug. 

    -How are you connecting the CC pins on your USB type C since they cannot connect to the BQ25890 device?

    -If you take a waveform of VBUS input power up do you observe VBUS initially at 5V before it steps up to 9V or does it start up directly at 9V?

    -When you set REG02 = 0x40 have you confirmed the device will read back a value of 0x40 from REG02 after configuration and do you have the watchdog disabled [REG07 bits 5:4]?

    Best Regards,

    Garrett