USB-PD-CHG-EVM-01: How to Tell Current?

Eric Castle

Part Number: USB-PD-CHG-EVM-01
Other Parts Discussed in Thread: TPS25750, BQ25792

Hello,

Is it possible for an MCU to request the USB charge/discharge current (preferably battery side, but I'll take either) over I2C? For example, could the MCU send messages to either:

The TPS25750, or
The BQ25792 (using the "I2Cr" command to get the TPS25750 to relay the request)

Alternatively, I suppose a status of something like "charging", "discharging", or "idle" might be sufficient for my application (but current would be easier to work with from a controls perspective).

Thanks,

-Eric Castle

over 1 year ago

0 Michael Emanuel35 over 1 year ago

TI__Mastermind 29935 points

Hi Eric,

The BQ25792 has an IBAT ADC (REG0x33). It can be read using the I2Cr via the TPS25750. From the below post, "In charge mode, ADC only reports charge current going into the battery. If your system load is more than the input power can support and the battery has to supplement the system load so that current is flowing in reverse from BAT to SYS, the ADC reports zero. The ADC only reports discharge current in HiZ mode with IBAT enable bit and in OTG mode."

In addition, please see Section 9.3.11.1 Charging Status Indicator (STAT Pin) for how the STAT pin behaves.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1012422/bq25792-how-to-measure-ibat?tisearch=e2e-sitesearch&keymatch=bq25792%2520negative%2520ibat#

Regards,

Mike Emanuel

0 Eric Castle over 1 year ago in reply to Michael Emanuel35

Intellectual 710 points

Hi Mike,

Thanks for the info.

If I understand, we can read the charging current only if the total system current is enough to flow into the battery (otherwise it reads as zero).

If I want to know if USB charging is occurring, is there a register I could read? Or is the STAT pin the only way to get this information?

Thanks,

-Eric Castle

+1 Michael Emanuel35 over 1 year ago in reply to Eric Castle

TI__Mastermind 29935 points

Eric,

You are correct, you can only measure the charging current if it is going into the battery. If you are in supplement mode, the ADC reports 0.

REG1C Charger Status 1 has a bit field called CHG_STAT that indicates charge status.

Regards,

Mike Emanuel

Power management

Power management forum

USB-PD-CHG-EVM-01: How to Tell Current?