• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 64 subscribers
  • Views 482 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.

BQ 24073 clarification

Ken Ishiguro
Prodigy 110 points
Other Parts Discussed in Thread: BQ24703, BQ24073

We are validating a 24073 design.  It works fine but I have a few questions:

1)  We selected too low a value for the charge timer resistor R_tmr versus the precharge time of the battery.   With a deeply discharged but good battery, the timer expires and fast charge mode does not start.  The timer will be corrected but how long does the USB charging source needs to be removed to reset the charge timer? (It seems to be a number of minutes)

2)  Charge current is fixed at USB500 through EN1/EN2.   The charge current resistor R_iset is selected for 600mA.  Please confirm it's irrelevant during fast charge (500mA) other than extending the dynamic charge timer period?

3)  Is precharge current is 10% of the resistor value (i.e. 60mA)  or 10% of USB500 set by EN1/EN2 ? 

4) The Charge status output toggles at 2Hz to indicate a time-out fault.  Is this true for a pre-charge error too?

5)  Datasheet is not clear whether the battery is cut off at a low voltage to prevent over-discharge.  Please clarify if this is true and the switch-off threshold voltage. 

6)  Datasheet refers to a "conditioning" phase...please explain further.

Thanks!

PS- Datasheet errata...the vertical scale of Fig 23-25 should be mA, not A!

  • 0
    Prodigy 110 points

    Any response to this?  It's a week old.  We resolved 5&6, still need 1-4 answered.

    Thanks!

  • 0 in reply to Ken Ishiguro
    TI__Prodigy 650 points

    Hello Ken,
    Here are the answers to your queries:

    1) Based on both what the datasheet mentions and result of my testing, to come out of the timer fault mode (and reset the timer), you simply need to toggle the input power OFF and ON (can be done immediately) once. It need not be turned OFF for any particular long period of time. Are you using an input capacitor? If that is the case, then what you're experiencing may be due to the capacitor taking some time to discharge, so the device is not really switching OFF until capacitor voltage goes below a certain value.

    2) Yes, ICHG will be limited to 500mA in USB500 mode, even if you have selected RSET for 600mA. Also, RSET does not affect the dynamic charge timer period. Timer values are only affected by the RTMR resistor.

    3) Pre-charge current is 10% of the value set by RSET.

    4) Yes.

    Regards,
    Rushil

  • 0
    Prodigy 130 points

    Hi Ken,

    5) I had the same doubt too. I have just experimentally checked using the EVM that when the "AC adapter" is not present the battery is left connected to to load even if it goes depleted. So load supply has priority over prevention of battery over-discharge.

    Regards

    Enrico

  • 0 in reply to Enrico Galletti
    Prodigy 130 points

    Ooops !

    I apologize but my test was about BQ24703 and not BQ24073.

    I do not know whether the rationale behind the two ICs is the same or not and thus if the have a similar behaviour.

    Sorry,

    Enrico

  • 0 in reply to Enrico Galletti
    Prodigy 110 points

    @Enrico- Thanks.  In our situation, another BQ2407x device has a pin to disconnect the battery from the load.   A simple resistor divider or voltage monitor on the output can be used to disconnect the battery.    However a charger or USB voltage must be applied to "unlock" and reconnect the battery.