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BQ25700A: PSYS function

K.Yaita
Guru 29720 points
Part Number: BQ25700A

Hi Team,

My customer is evaluating PSYS function of bq25700A however he saw non-linear feature as the following when Vbat=3.2V.
He increased VSYS current (system load) to get the data and VBUS (input source) isn't applied in this case.

x-axis: Battery Power[W]  *battery voltage[V] x battery discharge current[A]
y-axis: PSYS voltage[V]



Is it normal feature for bq25700A?

Best Regards,
Yaita / Japan disty

  • 0
    TI__Guru 56650 points

    After the PSYS goes up, the VSRN (battery voltage on charger side) is lower than the pre-charge threshold for this single cell application. The PSYS drops when the battery voltage is too low.

    Would you check the VSRN voltage and keep the battery voltage higher  enough to keep VSRN higher than the pre-charger threshold?

  • 0 in reply to Wang5577
    Guru 29720 points

    Hi Wang-san,

    Thank you for your reply.
    I will ask my customer to monitor VSRN voltage.

    I would like to ask just in case.
    Is pre-charge threshold you said following value?



    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    Guru 29720 points

    Hi Wang-san,

    My customer confirmed VSRN=3.075V when PSYS drop is occured.
    The datasheet shows Vbatlv_fall is 2.8V(TYP) so I believe it isn't the condition you said.
    May I have your further comments?

    In addition, which page of datasheet that describe the following feature?
    >The PSYS drops when the battery voltage is too low.

    Your support would be appreciated.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru 56650 points
    Right now, I checked our evaluation data and found a same result as you have. Like you said, the Vbat_fall is 2.8V. We are trying to find the right number for this PSYS test.
  • 0 in reply to Wang5577
    Guru 29720 points

    Hi Wang-san,

    I really appreciate for your kind support.
    My customer wants to know if it is expected feature or not for bq25700A so please inform if there is any update.

    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru 56650 points
    It is expected. I am trying to confirm the 3V is the minimum battery voltage for this PSYS function and its tolerance.
  • 0 in reply to Wang5577
    Guru 29720 points
    Is there possibility to modify the Electrical Characteristics on current datasheet?
    >Like you said, the Vbat_fall is 2.8V. We are trying to find the right number for this PSYS test.

    If so, I should inform to my customer.

    Best Regards,
    Yaita