• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Subscribers 62 subscribers
  • Views 472 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.

Original question:

BQ24070: Detailed Operation of Current Limiting, DPPM

BQ24070: The chip thinks there is a battery connected and in fast charge mode (According to STAT bits) even when no battery is connected. Am I missing something?

Jerry Molnar
Prodigy 210 points

Part Number: BQ24070

Tool/software:

Hello!

This design has been fully tested and now we are in pre-production mode.

One particular board had the charger working, but something changed and I'm trying to exhaust all possibilities before concluding that the chip is damaged.

With no battery connected, the status bits indicate that the chip is in fast charge mode. The BATT pins are static and at 4.2V - not cycling as per 8.4.3.5 of the datasheet which states:

"If the battery is absent, the BAT pin cycles between charge done (VO(REG)) and charging (battery recharge threshold, approximately 4.1 V)"

- The chip is running from a 5V supply (Mode = 5V).

- Power Good is asserted low.

- The CE pin is high

- ISET1 is at 0V (1K to GND and 100nF to BATT from ISET1)

When a battery is connected, it all the above is the same, but the charging current is 0.

Thanks in advance!

Jerry Molnar

Is the state machine stuck or something is holding it in the wrong state?
Is there a pin that I should check the state of?

  • 0
    TI__Mastermind 34260 points

    Hi Jerry, 

    Thank you for reaching out via E2E. I have a couple questions I'm hoping you can clarify. 

    -What is TMR pin connected to in your design? If you are able it is helpful to share the BQ24070 portion of your schematic. 

    Jerry Molnar said:
    When a battery is connected, it all the above is the same, but the charging current is 0.

    To confirm if you connect a not fully charged battery you observe expected voltage at BAT pin, but no charge current? If battery voltage is low enough (< 3V) will Status pins indicate precharge rather than fast charge? 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 210 points

    Hi Garrett,

    Thanks for your reply!

    Your questions:

    [1] TMR is connected to 82K to ground.

    [2] To confirm if you connect a not fully charged battery you observe expected voltage at BAT pin, but no charge current? Correct

    [3] If battery voltage is low enough (< 3V) will Status pins indicate precharge rather than fast charge? I will have to try this.

    To reiterate:

    I guess I'm trying to debug this particular board and understand:

    • what could possibly cause the device, when no battery is connected, to have the status pins report that it is in the fast charge state (Solid, not changing status bits)?
    • when a battery needing charging is connected, the status pins report the same - it appears to be in fast charge, but the charging current is 0. Same as with no battery connected.

    The external components all seem to be fine, but is there an external input that could be in the wrong state or wrong voltage and "fool" the device into thinking it should be fast charging?

    I should also add, that with the 5V input removed (which then forces CE low via pulldown) and a battery connected, the circuit load is powered by the battery. So there is continuity from the battery to the load.

    - AC_ADAPT_IN has a 10K pulldown
    - The cap on ISET1 is 100nF connected to BATT_CHARGER_IO. The resistor from ISET1 to ground is 1K.
    - R7 is the 82K connected to TMR; The 0 ohms  from TMR to VREF is not populated
    - DPPM has a 36.5K in parallel with 10nF to ground.

    To recap - the board had been working fine...something changed and now it is behaving as I described.


    Thanks!
    Jerry

  • +1 in reply to Jerry Molnar
    TI__Mastermind 34260 points

    Hi Jerry, 

    Thank you for your answers and further explanation. Please see my comments below.

    Jerry Molnar said:
    what could possibly cause the device, when no battery is connected, to have the status pins report that it is in the fast charge state (Solid, not changing status bits)?

    I asked about TMR pin because this behavior could be explained by termination being disabled. With termination disabled the device would continue to regulate BAT pin to 4.2V and status pins would indicate fast charge state. 

    With that said given the device does not charge when a battery is connected and charge is properly enabled it does appear likely that damage occurred given the board was previously working without issue. I cannot point to anything in the setup that would have the device stuck or "fooled" in the wrong state. 

    Jerry Molnar said:
    To confirm if you connect a not fully charged battery you observe expected voltage at BAT pin, but no charge current? Correct

    Only other behavior I would be interested in verifying is the following. Is OUT regulated properly and able to support your system load for the case where 5V input and battery are connected, but not actually being charged? 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 210 points

    Hi Garrett,

    Thanks for your reply.

    In case this is telling, the voltage at TMR is 0.71V.

    Is OUT regulated properly and able to support your system load for the case where 5V input and battery are connected, but not actually being charged? 
    Yes, the OUT is 4.4V and nice and clean.

    Also...the thermistor was not connected. That input has a 10K pulldown to ground on the PCB .

    Best Regards
    Jerry

  • 0 in reply to Jerry Molnar
    TI__Mastermind 34260 points

    Hi Jerry, 

    Thank you for your response. 

    Jerry Molnar said:
    In case this is telling, the voltage at TMR is 0.71V.

    Referring to the end of datasheet section 8.3.1.1.3 and note (9) on page 7 TMR is expected to be regulated to 2.5V during normal operation. If in DPPM TMR voltage will reduce. 

    Now the lower TMR voltage may be a result of IC damage or it may indicate the issue is related to DPPM. Considering you report OUT voltage = 4.4V the device does not appear to actually be in a DPPM operation. 

    At this stage the best next step to verify device damage or not would be to perform an ABA swap with another working board to determine if the issue follows the chip or the board, but that is up to you whether you wish to perform said action. 

    Best Regards,
    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 210 points

    HI Garrett,

    Thanks once again for your help and insights. Much appreciated. I'll give the DPPM elements one last check. If it all looks good, I'll swap the part out and let you know the results.

    Best Regards

    Jerry