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BQ25703A: How to set the VBUS over voltage/undervoltage in OTG mode?

Arnaud MONTEZIN
Prodigy 210 points
Part Number: BQ25703A
Other Parts Discussed in Thread: BQ25703

Hello,

On the datasheet bq25703A, SLUSCU1A –MAY 2017–REVISED MAY 2018, p14,

the VBUS_OTG_UV and VBUS_OTG_OV are a percentage of the ouput voltage in OTG mode, respectively 85% and 105%.

Is it possible to change these percentages?

regards,

Arnaud MONTEZIN

  • 0
    TI__Mastermind 25800 points
    Hey Arnaud,

    Unfortunately, these thresholds cannot be changed. You can potentially change the output voltage to achieve the threshold you need, or potentially use the integrated comparator on the charger to disable the OTG_EN pin to give you control over the upper or lower limit as a hardware workaround.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 210 points
    Hello Joel,

    In first, many thank for your answer.

    To be more precise, our need is to increase the OV threshold form 105 % to 120% or more.

    Removing or ignoring the OV could also solve our problem. But, it seems not possible.

    And, because it is not possible to change the threshold, you proposed two methods :

    1) change the output voltage to achieve the threshold you need

    2) use the integrated comparator on the charger to disable the OTG_EN pin to give you control over the upper or lower limit


    The first method is not suited to our architecture because the calculation and transfering time from the host down to the BQ25703 for changing the voltage could exceed the UV/OV 7ms masking time.

    For the second method, it will allow :
    - to increase the UV from 85% up to 97/98% nominal output voltage
    - to decrease the OV threshold from 105% down to 102/103%
    => so its not not possible to increase UV threshold up to 120%? Does I well understand?
  • 0 in reply to Arnaud MONTEZIN
    Prodigy 210 points

    hello Joel,

    If my question isn't any clear, let me know.

    Waiting for your answer,

    regards,

    Arnaud MONTEZIN

  • 0 in reply to Arnaud MONTEZIN
    TI__Mastermind 25800 points
    Hey Arnaud,

    I didn't understand. What do you mean increase the UV threshold to 120%? Do you mean to 80% of the OTG voltage?

    In either case, the charger only has a single comparator input/output, so you can only monitor one parameter at a time, either UV or OV, but not both. With an extra external comparator, you can potentially implement both UV and OV.

    The end goal here would be to use the comparator output to pull the EN_OTG pin low.


    Regards,
    Joel H
  • 0 in reply to Joel Hernandez II
    Prodigy 210 points
    Hello Joel,
    Sorry, I have done a mistake on the following sentence witch creates confusing. I am sorry.

    Instead of :
    "=> so its not not possible to increase UV threshold up to 120%? Does I well understand?"

    you must read :

    => so its not not possible to increase OV threshold up to 120%? Does I well understand?

    We would like to increase the OV threshold up to 120% or more , or to ignore the OV fault.

    is it possible?

    regards,
    Arnaud MONTEZIN
  • 0 in reply to Arnaud MONTEZIN
    TI__Mastermind 25800 points
    Hey Arnaud,

    Sorry, I had misunderstood your question before. I understand now.

    Yes, unfortunately the BQ25703A OTG limits are fixed to 85% for UV and 110% for OV. There is not way to increase the window further.
    I originally believe you wanted to tighten the limits, which is possible, meaning UV can be greater than 85% or OV can be less than 110%, but not other way around.


    Regards,
    Joel H