BQ25890: VBAT data read back is inaccuracy

Jason,

Is VBUS applied or not?  If not, what is the MINSYS value?  When no VBUS is applied, the ADC is only accurate if V(BAT)>MINSYS value.  If your customer lowers the MINSYS to 3.0V (the lowest setting) does the ADC function properly.

Regards,
Jeff

Hi Jeff,

We confirm there is no VBUS applied during the time we captured error log.

We set the MINSYS to 3.0V at battery discharging period.

BTW, We tried to set the MINSYS back to default 3.5V (REG03), and using the 3.2V battery to power our device. At this time, the ADC of VBUS/VBAT/VSYS values were all 0x0. ADC conversion function was turned on.

BR,

Joseph

Joseph,

I'm not aware of any issues with the VBAT ADC.  Are the other ADC values accurate when no VBUS is applied? Does this happen on multiple boards/ICs?

Regards,

Jeff 

Hi Jeff,

According to our above error log, it indicates:

VSYS(REG0F) is 3.464V.

VBAT(REG0E) randomly changes from 3.684V to 3.804V within 18 seconds.

TBAT(REG10) is -18.288degC.

 None of these values are reasonable at that moment, because it was room temperature environment, and we made our device discharge.

Here is how BQ25890 works good to us.

VSYS is around 3.1V.

VBAT is around 3.1V.

TBAT is 28.85degC.

All these values fit real ambient temp and real battery voltage.

These abnormal values were ever found on 3 devices ( all manufactured at same sample build ). However, its quite hard to be reproduced.

BR,

Joseph

Joseph,

Where did you measure VBAT voltage by digital meter?

Thanks,

Ning.

Ning,

Remove the Battery from our device, and measure its voltage between Pack+ and Pack- directly.

BR,

Joseph

Hi All,

We confronted a more weird read values from the BQ25890.

The situation is:

1. Chamber is controlled at 40degC.

2. Adapter is plugged (QC2.0 standard).

*TIC refers to on board NTC placed near BQ25890.

Weird points I think:

1. Adapter is plugged but REG0B shows VBUS status is "No input".

2. VBAT is 4.844V. REG-6 register setting shows we correctly set limit to 4.208V, which refers to our VMAX value.

3. When ADC functions becomes abnormal, TBAT ( REG10) is -18.288, no matter room temp or 40 degC chamber.

Besides the wrong ADC values, "no input" status of VBUS will cause MCU mistakenly set VSYSMIN to 3.0V while there is a powering adapter.

BR,

Joseph