• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 733 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25892 battery monitor ADC in battery-only mode

Sam Litvin
Prodigy 100 points
Other Parts Discussed in Thread: BQ25892

Using the BQ25892, we thought that the battery monitor was not working at all when in battery-only mode.  (See SR# 1-1910662095)  Upon further investigation, we have determined that the battery monitor works properly until the battery voltage falls below ~ 3.59v (Register 0x0e reads 0x3d) at which point register 0x3d always reads 0x00.  The full datasheet says nothing to suggest that this is proper behavior.  Is there some was to get valid ADC readings all the way down to ~3.0v?

  • 0
    TI__Guru**** 166506 points
    Unfortunately, the minimum battery voltage for accurate ADC measurement without input voltage is VSYSMIN, as documented on d/s page 10 in the ADC section under VBAT_RANGE.
  • 0 in reply to Jeff F
    Prodigy 100 points

    OK, I see that now, but perhaps the datasheet could be improved to make it more clear in the text of section 9.2.8.  Also this is really unfortunate behavior because it means that you loose a good chunk of battery capacity if you want to be able to guarantee a clean shutdown at a known battery level.  I assume this has something to do with the REGN LDO?  Could we drive the REGN rail from an external source?  (e.g. we have a 5v boost regulator elsewhere in our system)

  • 0 in reply to Sam Litvin
    TI__Guru**** 166506 points

    Can you write the SYSMIN value = "000" just before you go into battery-only mode?  This should let you run the ADC with a battery as low as 3V.