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BQ24650: Maximum duty cycle at 80 degrees C

Bastien CURUTCHET
Prodigy 100 points
Part Number: BQ24650

Hi Team,

I am considering using BQ24650 for a customer application requiring the following specification:

Battery voltage: 27.3V

Constant current requirement:1.2A

Temperature : 0-80 degrees C

I saw in an other e2e thread that the maximum duty cycle for this chip if you want to keep regulation is 97%. With 28V in input 97% of duty cycle gives 27.2V in output, it could fit but I'm afraid to be too closed to the limits of the chip especially at 80 degrees.

Do you think this chip would fit for this application ?

Thank you,

Bastien

  • 0
    TI__Expert 8690 points
    Bastien,

    This voltage seems very close and as you mention at around 97% you might get pulse skipping. Either lower the battery voltage regulation point to 27.1V or increase the input voltage to at least 95% duty cycle.

    Regards,
    Steven
  • 0 in reply to Steven Bangdiwala
    TI__Prodigy 100 points
    Hi Steven,

    Thank you for your answer.
    I thought about increasing Vin to 29.6V but the datasheet says the limit for VCC and SRP is 28V. I could increase R6 (page 1 of datasheet) to get Vcc under 28V but the problem remains for SRP doesn't it ?

    Regards,
    Bastien
  • 0 in reply to Bastien CURUTCHET
    TI__Expert 8690 points

    Bastien,

    You can use 29.6V if it is stable. The lower limit of ACOV is 31V, where you can use 30V as the max input voltage as long as the input voltage is stable enough.

    Regards,
    Steven

  • 0 in reply to Steven Bangdiwala
    Prodigy 20 points
    Hi Steven,

    This is Sergio Ruiz, the customer who Sebastien is supporting to. In fact, I would like to have two different voltage for charging a lead Acid Battery. Overcharge voltage at 28.8V and floating voltage at 27.3V. After charging I would like to maintain floating voltage. In order to maintain voltage I have to Disable the Termination, forcing the TERM-EN pin to Low. In order to switch from 28.8V to 27.3V, I would like to use the STAT2 PIN, who goes to ON when charge is complete. My question is: If I disable the Termination, will the STAT2 Pin go to ON when the battery is charged?
    Regards

    Sergio
  • 0 in reply to sergio ruiz
    TI__Expert 8690 points
    Hi Sergio,

    Welcome to the E2E forum!
    In order for the charger to go into charge complete state, it has to terminate. So by disabling termination, I believe STAT 2 will not go to ON state. You can, however, modify our charger in order to enable pulse charging by following this app note: www.ti.com/.../slva437a.pdf

    Using STAT2 will not maintain ON state forever if you change VFB resistors to charge at 27.3V, because once charging starts, it will go back to STAT2 OFF.

    You would need a comparator with a hysteresis to control the TERM_EN and VFB resistors, where the hysteresis allows battery voltage to go down to 27V.

    Regards,
    Steven