• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 62 subscribers
  • Views 842 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.

BQ25713: ACOV bit set unexpectedly

Dan Closson
Prodigy 170 points
Part Number: BQ25713
Other Parts Discussed in Thread: BQ25173

We are currently testing a new battery charger design that is based on the BQ25713 EVM module. I've seen this a couple times now where the charger appears to be working fine and charges a battery and then suddenly stops working. When it stops working these are the symptoms:

  1. When I connect VBUS from a bench top powersupply to try and charge the battery I hear an audible noise from the inductor and no current is drawn from the supply even when setting the charge voltage and current levels.
  2. The ACOV bit is set in the Charge Status Register?? I've measured with a scope and don't see any over voltage on VBUS. Why is this bit being set?
  3. The VREG LDO is coming up but I can see a periodic voltage spike riding on top the 6V waveform (also a periodic oscillation on VBUS)
  4. If I remove the battery and power the load from VBUS the switcher comes up and supplies power to the load (about 0.5A) with VSYS at 9V.

This is a new design and we're seeing quite a bit of fallout with the battery charger IC (BQ25173) on this first prototype so I'd like to understand this failure and hopefully determine the root cause. Any ideas why the ACOV bit is set and the battery charger is not charging when a battery is present?

Thanks,

Dan C.

  • 0
    Prodigy 170 points
    UPDATE: After looking a bit closer I noticed that both the ACOV and BATOC bits are toggling when reading the ChargeStatus (0x20) register. Looking closer at the battery current sense resistor I notice that the voltage drop across the sense resistor when measured across the kelvin sense lines is 700mV while directly across the sense resistor itself is almost 0. Using a multimeter I measure about 150k between the kelvin sense line and the pad. Upon lifting the sense resistor I see that the kelvin trace looks blackened where it connects to the pad. After replacing the sense resistor and adding a flywire to connect the pad and kelvin sense line this unit starts charging again.

    I'm concerned that the burnt up trace was a symptom of some other issue? Any ideas on what would cause this behavior? I know that this unit was working and then suddenly stopped working.

    Thank you.
    Dan C.
  • 0 in reply to Dan Closson
    TI__Mastermind 25800 points
    Hey Dan,

    It's hard to say for sure. If your Kelvin sense trace is close a heavy power area with little heat dissipation, it could be burning up due to proximity.

    If the IC is getting damaged due to some actions that forces the voltages outside of the Absolute Maximum Rating, that could potentially be an issue. Such things can happen, for example, if the battery is removable and a large amount of inrush current is present, causing an over-voltage on SRP or SRN.

    And based on your original posting, the facts that REGN rises above 6V with a spike, it is very concerning that you may be damaging the charger at that node or VDDA.

    I would re-compare your schematic to the EVM schematic and note any major or minor differences in components, components voltage ratings, or components types.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 170 points
    Thanks for the response Joel! I double checked our schematic with the EVM and don't see any glaring differences that would account for this. Although, you make a great point about inrush current. We are using 10mOhm sense resistors same as the EVM and I notice that the SRP/SRN inputs are only rated for differential voltage of +/- 0.5V which corresponds to 50A across the sense resistor. This unit was used in testing and it is very possible that the output was shorted with a battery installed which would result in a huge fault current likely in excess of 50A. Does TI have a recommendation for protecting current sense inputs on the BQ27513 if we anticipate high inrush or fault currents? Perhaps a schottky across the inputs? Thanks for your support.
  • 0 in reply to Dan Closson
    TI__Mastermind 25800 points
    Hey Dan,

    In reality, the 10-Ohm resistors on SRN and SRP are intended to be damaged in the event of a reverse battery plug-in in lieu of damaging the charger. However, for an over-current I would recommend some battery protection circuitry to disable the discharge path of the battery cell to the rest of the system in the event of a short.


    Regards,
    Joel H