BQ25638: BQ25638 Charging query

Hi Star,

We will check and get back to you.

Thanks,

Ning.

Hi Star,

We need additional information to be sure of the causes of these behaviors: 

Star Xu said:

The 10-30mA VBUS input has a set current value input, but the battery terminal does not. current value. What is the reason for this phenomenon?

For your first question, what are VREG, VRECHG, ITERM, and EN_TERM set to?  And what does the CHG_STAT register state?

Star Xu said:

ICHG configures 3200mA, 3.0V and enters fast charging to 3.5V. The fast charging current is 3.2A. When it reaches 3.5V, the fast charging current will jump to about 3.4A.

What is the reason for this phenomenon?

For your second question:

• What VIN voltage and current is connected?
• What is VSYSMIN set to? 
• What does CHG_STAT state?
• Are VSYS_STAT, VINDPM_STAT, or IINDPM_STAT set to 1? 
• What method is used and what accuracy do you estimate for your fast charge measurement?

Thank you!

Katherine Huckabay 

Hi TI team，

For your first question, what are VREG, VRECHG, ITERM, and EN_TERM set to?  And what does the CHG_STAT register state?

A:VREG=4.2V,VRECHG=4.0V(VRECHG bit  set to 1),EN_TERM set to 1.The CHG_STAT is Fast Charge (CC).

For your second question:

• What VIN voltage and current is connected?  ->5V 3A DC POWER
• What is VSYSMIN set to?  ->VSYSMIN set to 3.52V
• What does CHG_STAT state? ->  Fast Charge (CC)
• Are VSYS_STAT, VINDPM_STAT, or IINDPM_STAT set to 1? ->VSYS_STAT=Not in VSYSMIN regulation,VINDPM_STAT=Normal,
• What method is used and what accuracy do you estimate for your fast charge measurement?->Charge the battery simulator with 5v/3a dc POWER, set the initial voltage of the simulator to 3.3V, then adjust the battery simulator voltage to 3.5V，The charging current should be 3.2A±3%

Hi Eajon,

For your first question:

We are working to replicate the behavior your team has observed and will have results by the end of tomorrow.  We have a few more questions:

• Is VINDPM_STAT, VSYS_STAT, or IINDPM_STAT set to 1? 
• We are not sure if the bq27z746 has enough resolution at those low of currents.  Could you confirm the results through another method such as connecting a sense resistor and a multimeter? 

For your second question:

• The ICHG accuracy is +/- 5% and if the measurement accuracy is an additional +/- 3% then 3.4A is within spec.  The change is seen due to the battery voltage approaching VSYSMIN.  This will cause the BATFET to change from linear mode to PWM mode and may cause an increase or decrease in battery charge current.
• Was this increase to 3.4A observed on one device or multiple devices? 

Thank you!

Katherine Huckabay 

Hi Katherine,

  VINDPM_STAT  set to 1,VSYS_STAT and IINDPM_STAT set to 0.

Could you confirm the results through another method such as connecting a sense resistor and a multimeter? 

->We connected the bq25638EVM directly to the battery simulator, and the test results were the same.

For your second question:

• Was this increase to 3.4A observed on one device or multiple devices? ->multiple devices.

Thank you!

Hi Katherine,

 Because our products need to support 10-30mA charging current.VINDPM set to 4.72-4.8V.10-30mA charge is ok at 4.1V,but I wonder if this will have a bad effect on the charging IC.

 Thank you!