BQ25790: cannot terminate charging

Hi Ann,

The termination accuracy is a function of charge current setting.  If the charge current setting is set to below 1A, does the charger terminate as expected?

Regards,

Jeff

Hello Jeff,

Will try and let you know, but could you provide your opinion for this case and I can discuss with my customer. What is the meaning for "The termination accuracy is a function of charge current setting"? Since 160mA vs. 720mA is large step, I'm not sure if it is related to accuracy. Thanks a lot!

Best regards,

Ann Lien

Hi Ann,

All of our chargers use the BATFET to measure current.  When the charge current setting is above 1A, the charger turns on more parallel paths to make the BATFET less resistance for higher efficiency.  This causes the current measurement across the lower resistance to be less accurate for low currents.  So, to make the current measurement more accurate at lower currents, the BATFET needs to be more resistive.  Lowering the charge current for the 790 family below 1A makes the BATFET more resistive and therefore provides more accurate measurement at lower charge currents. 

Regards,

Jeff  

Hello Jeff,

Customer tested with below condition and it still cannot terminate charging. May we know if below setting is correct or wrong for your opinion? We've already set charging current less than 1A. Thanks a lot!

REG01 CHARGE VOLTAGE       01A5         4210mV

REG02 CHARGE CURRENT       0046        700mA

REG06 INDPM                         0078        1200mA

REG08 PRECHARGE CURRENT 04           160mA

REG09 TERM CURRENT           04            160Ma

REG0E CHARGER TIME AND TOPOFF TIMER SETTING  79H    Topoff Timer  15MIN、charge timer 5hrs

REEG2E  ENADC                      B0            ENABLE

Best regards,

Ann Lien

Hi Ann,

If Topoff timer is set to 15 minutes, the charger will not terminate until 15 minutes after the charge current tapers down to 160mA.

Regards,

Jeff

Hello Jeff,

So we need to disable top-off timer then we can terminate charging, right? Thanks a lot!

Best regards,

Ann Lien

Hello Jeff,

Customer has disabled top off timer and result is the same. May we know if you can help to check the attachment for status from customer's board to see if there is anything missing. Thanks a lot!

/cfs-file/__key/communityserver-discussions-components-files/196/BQ25790_5F00_1213_5F00_TEST.xlsx

/cfs-file/__key/communityserver-discussions-components-files/196/BQ25752_5F00_1213_5F00_REGISTER.txt

Best regards,

Ann Lien

Hi Ann,

I can't explain why the charger isn't terminating.  In fact, I can't explain why it does not enter topoff timer charge when ICHG is close to ITERM=160mA.  It should enter topoff after ICHG<=160mA typical and V(BAT)>BATREG-VRCH. I have tried to recreate on the bench with the customer settings and my device enters taper, then topoff and then terminates correctly each time.   

The charger is behaving as if termination and top timer are disabled.  But per the registers, EN_TERM =1 (REG0x0F[1]).  The charger only auto disables termination if the charger is in IINDPM, VINDPM or thermal reg but none of those states are being reported.

Does this happen on all units or only 1 unit?  What is the top marking on the IC?  If ADC is disabled and PFM is disabled, does the charger enter topoff timer and terminate as expected?  

Regards,

Jeff

Hello Jeff,

I will order one EVM for BQ25790 to test with the same condition after EVM is arrived at 12/22. it happens in every customer's board. but customer used BQ25792 EVM to do the same test can terminate charging successfully. So we think it is related to customer's setting or hardware. May we know if there is any clue on hardware on this case we can check? Thanks a lot!

Best regards,

Ann Lien 

Hi Ann,

I am not aware of a difference between 790 and 792 termination functionality.  

Regards,

Jeff

Hello Jeff,

After checked with BQ25790 EVM, I found out the same behavior as customer's board, cannot terminate charging.

When I set termination current to 720mA, it will show not charging during current from 400~600mA to 0mA(used source-meter to change battery voltage up 0.01V/steps). May we know if you could double check if it is also observed on your EVM? Or any hardware setting we didn't set well? Thanks a lot!

Best regards,

Ann Lien

Hi Ann,

My EVM terminates correctly with the settings you provided above.  What is the input voltage at VBUS when you are trying to terminate?  I recently found that if VBUS is close to VBAT, the charger has issues terminating.

Regards,

Jeff

Hello Jeff,

VBUS is 5V which is USB power. May we know if there is any limitation or equation for VBUS/VBAT so that we can know how close the VBUS/VBAT is will cause this issue? Thanks a lot!!

Best regards,

Ann Lien

Hi Ann,

There is no known equation.  The issue I found with another customer was a corner case with a certain load on SYS and VBUS close to VBAT.  What is the load on SYS? Is it a DC load or transient load?  If PFM mode is disabled, does the charger terminate as expected?

Regards,

Jeff