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BQ24650: STAT1 and STAT2 cycle blink when battery is fully charged

Michel Fripiat
Prodigy 90 points
Part Number: BQ24650

Hi team,

Within our application, the bq24650 blinks periodically STAT1 & 2 with the following cycle steps :

STEP number STAT1 STAT2 Supposed charge state
1 ON OFF Charge in progress
2 OFF ON Charge complete
3 ON ON Fault (?)
4 - - Go back to step 1

For a better understanding of the situation and the time elapsed between each steps, please take a look at this video

The cycle period is slower when current is lower.

Nominal battery voltage is 12V and lead acid. During  the video, the voltage is around 13.3V so we assuming battery is fully charged.

Our question : Is it a normal situation ? Because we assume when battery charging is completed, charge complete state should be idle and stable.

Regards,

Maxime.

  • 0
    TI__Mastermind 25800 points
    Hey Maxime,

    From your video, I don't see STEP number 3. It looks like Charge in progress, then Charge complete, then the two LEDs are off which would indicate charging suspended.

    Can you take a oscilloscope capture of the VSRN voltage, VFB voltage (much smaller voltage/division), IBAT (charge current), VCC voltage AND change monitor it with a 500ms to 1s time scale?

    Do you also have a schematic you can provide?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 90 points

    Hello Joel,

    Ok, sorry you are right, when both LED are off, then the charge means suspend. There is no fault state during step 3. (Also we figure out a mistake on the pcb silkscreen. STAT1 & 2 have been reversed during design process). 

    But we didn't expect it would loop like it shown on the video. Taking a look at the 'Figure 14. Operational Flowchart on datasheet' p.21. it is quite confusing to understand which path the bq25650 is taking in our case and when a suspend state can occur. Can you elaborate this ?

    Regards,

    Max

  • 0 in reply to Michel Fripiat
    TI__Mastermind 25800 points
    Hey Max,

    The suspend case can occur if the charger happens to hit the SLEEP condition. You mentioned your battery regulation voltage is set to 13.3V. What is your input voltage, as measured from VCC? If it is too close, you could potentially be entering and exiting the sleep condition?


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 90 points

    Hello Joel,

    The 13.3V is the battery voltage we measured when the charge status indicated complete. In our application the regulation voltage output is set to 13.61V by the two programmed resistors. We noticed this regulate voltage level occurs not on every cases but often when fast charge mode is enabled by the bq24650.

    The input voltage is the one provided by a 36 cells solar panel. So typically it is around 18.0V (17.6V @max Power). So I don't think the input voltage was close enough to charging voltage at this time. There might be another reason but we can't related. Any hints or ideas ?

    Regards,

    Max.

  • 0 in reply to Michel Fripiat
    TI__Mastermind 25800 points
    Hey Max,

    Are you utilizing the MPPSET pin of the charger to regulate the solar panel voltage? If you allow the charger to pull as much current as it wants from the panel without regulation, the panel voltage will easily collapse below the SLEEP comparator and stop of the converter.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 90 points

    Hi Joel,

    Sorry for the late response.

    > "Are you utilizing the MPPSET pin of the charger to regulate the solar panel voltage? ..."

    No, We just use it when we want to enable/disable the charge of the battery by the solar panel but do not regulate the panel voltage with MPPSET. Should we ?

    > " ... If you allow the charger to pull as much current as it wants from the panel without regulation, the panel voltage will easily collapse below the SLEEP comparator and stop of the converter ... "

    That is interesting. So due a high current drain, a significant voltage drop could drop down the voltage below the SLEEP threshold for a short amount of time to trigger the SLEEP comparator ? Is that what you mean ?

    Regards,

  • 0 in reply to Michel Fripiat
    TI__Mastermind 24075 points

    Hi Maxime,

       As Joel mentioned, yes if you have high current drain and the input supply is unable to provide power, it results in voltage droop to compensate. If the output power required is enough to cause voltage to drop to your battery voltage, you will enter sleep mode and suspend charge. Section 8.3.2 of the d.s details how to regulate input voltage using MPPSET.

    An oscilloscope capture with the pins Joel mentioned in the first comment will be helpful to see if we are entering sleep mode, or if another mode is interfering.

  • 0 in reply to Kedar Manishankar
    Prodigy 90 points

    Hello Kedar,

    I think did a little mistake regarding my answer to the question of Joel about MPPSET pin. According to our schematic, it seems regulate by R104 and R106. Sorry about that

    I can't capture the MPPSET with a scope right now. But we are looking to do it as soon as possible.

    Regards.

  • 0 in reply to Michel Fripiat
    TI__Mastermind 24075 points

    Hi Maxime,

      In the meantime it will also be useful if you can capture IBAT and VBAT when you see STAT pin charge/suspend/resume charging.

  • 0 in reply to Kedar Manishankar
    TI__Mastermind 24075 points
    Hi Maxime,
    We haven't heard back from you. We are assuming you were able to resolve your issue. If not, just post a reply below or create a new thread if the thread has locked due to time-out.
  • 0 in reply to Kedar Manishankar
    Prodigy 90 points

    Hi Kedar,

    We didn't have the opportunity to reproduce the issue and record the pins as you suggested but we will continue to track the problem if it does occurs again. 

    In the meantime, thread can be set as resolved.

    Thank you for your support.

    Regards,

    Maxime Dolberg.