• State
  • Replies 7 replies
  • Subscribers 63 subscribers
  • Views 100 views
  • Users 0 members are here
Support feedback
Options
Options
Related

BQ25125: BQ25125 stops responding on i2c

Omar Kiyani
Prodigy 10 points
Part Number: BQ25125

Tool/software:

Hello,

I’m using the BQ25125 in my design and running into an I²C communication issue. The MCU is operating at 1.8V logic, and I can communicate with the BQ25125 without problems when VSYS is below 2.9V.

However, once I raise VSYS above 2.9V, the BQ25125 stops responding on I²C. The MCU is still running fine at 1.8V, but SDA/SCL transactions no longer get ACKs from the device.

Some details:

  • MCU I/O voltage: 1.8V

  • BQ25125 powered normally from battery/VSYS

  • I²C lines pulled up to 1.8V

  • Communication is fine at lower VSYS values

  • Issue only occurs when VSYS > 2.9V

  • 1.8V is sourced from LDO of BQ25125

  • VBAT and charger is connected
  • 0
    TI__Genius 17885 points

    Hi,

    Can you please share the schematic of your BQ25125 implementation.

    Omar Kiyani said:
    Issue only occurs when VSYS > 2.9V

    This VSYS voltage is changed via I2C register change?

    Also, what are your VIN and VBAT voltages during this testing?

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 10 points

    Hi Juan, 

    I can share a schematic screenshot:

    Yes, I change VSYS from the I2C register.
    VIN (USB) is around 5.1V
    VBAT is around 3.8 or 3.9 depending on the SOC of the battery but as our charger is always connected for this test, VBAT is not in UVLO.

    Thanks for your response!
    Omar

  • 0 in reply to Omar Kiyani
    TI__Genius 17885 points

    Hi Omar,

    It's unexpected that raising the VSYS configuration while power is available should cause I2C to fail. Can you provide any waveforms for when VSYS is configured above 2.9V? Can you confirm the voltage on VSYS at the time?

    Also, is there a load present during this testing? 

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 10 points

    Hi Juan, 

    While reading through BQ25125 FAQ I came across this.

    The datasheet does not mention this anywhere! 

    Also look here:

    My pullups are 1v8. It should work! 

    The datasheet and FAQ are at odds to each other.

  • 0 in reply to Omar Kiyani
    TI__Genius 17885 points

    Hi Omar,

    The I2C should work with external pull ups to 1.8V, though I'll confirm this behavior. I believe this more relates to the SYS Good signal internal to the device. It requires that the SYS rail is able to output voltage close to the configured value in order to confirm that the SYS rail is good. The SYS rail is internally used to bias some I2C level shifters so if it is not good the device disables the I2C communication.

    When you configure your SYS rail to >2.9V, can you confirm the voltage present on the SYS rail matches the configured voltage?

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 10 points

    Hello Juan,

    Yes, if I configure the SYS rail to 3v3, the SYS rail measures 3v3 but I cannot communicate with the chip anymore. 

  • 0 in reply to Omar Kiyani
    TI__Genius 17885 points

    Thank you for the confirmation. On bench testing I've been unable to recreate this behavior, but I will try with a couple different set ups to confirm this.

    Best Regards,

    Juan Ospina