bq24171 - Error Conditions

Adam, 

Since the bq24171 is a standalone charger, there really isn't much in terms of smart fault diagnostic options as you would have with one of our host controller chargers. 

Here is a basic overview of possible faults:

• Timer Faults
  • Fast Charge Timer(TTC) expires:
  • Pre-charge timer expires: On power-up if VBAT < VLOWV threshold, the bq24171 the pre-charge current to the battery.  If after 30min the VLOWV threshold isn't reached, the charger turns off and a fault in indicated.
• TS fault
  • If TS pin is outside of safe charging threshold - charge is suspended and STAT blinks
• Short Circuit Protection
  • Cycle-by-cycle current monitoring feature achieved by monitoring the voltage drop across Rdson of the MOSFETs.  Charger will latch off and STAT pinwill report fault condition. can be =reset by removing and re-plugging the adaptor 
• Input Over-voltage
  • OVPSET rising > 1.6V typ
• Battery over-voltage
  • VBAT > 104% of regulation voltage.  If over-voltage persists longer than 30ms, charge is disabled
• Battery Absent
  • See figure 18 on page 20 for battery absent conditions

   

Let me know if this summary helps, or if there is more information I can provide.

Thanks,

Rachel 

Hi,

Sorry for the delayed reply.  For some reason I didn't get notified of your answer, and then this project got sidelined for something else.

Here's some more information on what I'm seeing, along with some questions about the error conditions. 

-The circuit doesn't charge, but it does switch between the 12V supply and the 2 cell lithium battery as it should.

• Timer Faults
  • Fast Charge Timer(TTC) expires:
  • Pre-charge timer expires: On power-up if VBAT < VLOWV threshold, the bq24171 the pre-charge current to the battery.  If after 30min the VLOWV threshold isn't reached, the charger turns off and a fault in indicated.

-Blinking starts as soon as 12V power is applied, so timer faults are ruled out

• TS fault
  • If TS pin is outside of safe charging threshold - charge is suspended and STAT blinks

The NTC measures 11k, and TS is at 2.163V, which should be OK

• Short Circuit Protection
  • Cycle-by-cycle current monitoring feature achieved by monitoring the voltage drop across Rdson of the MOSFETs.  Charger will latch off and STAT pinwill report fault condition. can be =reset by removing and re-plugging the adaptor

I suspect this may be the problem.  Which MOSFETs does it check? The two driven by ACDRV, the one driven by BATDRV, or all 3? What are the allowed values for the voltage drop?  All 3 appear to be fine when I check them. 

• Input Over-voltage
  • OVPSET rising > 1.6V typ

OVPSET pin reads 1.092V

• Battery over-voltage
  • VBAT > 104% of regulation voltage.  If over-voltage persists longer than 30ms, charge is disabled

VBAT is 7.91V

• Battery Absent
  • See figure 18 on page 20 for battery absent conditions

Battery is present.

Thanks

Hi Rachel,

It's my own, but it is based off of the EVM schematic and uses almost all of the same components.   I can email you a copy of the bq24171 section if you like.  I should also add that this design was working quite well for a few weeks, then inexplicably went into the "problem" mode.  I'm trying to diagnose what changed to trigger the error condition, but so far I'm stumped.

Adam,

If it was working fine before, my guess is something has been damaged. I would suggest checking the external FETs first. 

Thanks,
Rachel