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BQ25703A: About the drive capacity of /BATDRV pin

Tsukui Yusuke
Guru 21930 points
Part Number: BQ25703A
Other Parts Discussed in Thread: CSD25402Q3A

Hi,

Please tell me about the drive capability of /BATDRV pin and the compatibility with the FET under consideration.
The input voltage is 19V, the system voltage is 16.8V, and the battery in use is 4 cell Li-ion.

Customers are considering the following FETs.
・TPCA8120
・RS1E260ATTB

1.
The data sheet has the following description.
However, it cannot be determined whether the above FET can be driven.
Is it possible to drive the above FET?

2.
If /BATDRV performs maximum output operation, is there a possibility that BA25703A will operate unstable?
What happens to the BQ25703A if the Pch gate cannot be set to High completely?
Could you give me your advice?

Best regards,
Yusuke

  • 0
    TI__Mastermind 24075 points

    Hi Yusuke-san,

       From the datasheet: The BATDRV pin is only able to drive a battery MOSFET with Ciss lower than 5nF. The Ciss in the range of 1nF~3nF is recommended.

    I was not able to find the 2nd mosfet option online, but the 1st option has 7820pF Ciss which would be too high. You can also consider the MOSFET used on the EVM board: CSD25402Q3A (Ciss = 1380pF)

    Yes operation could be unstable if BATDRV cannot drive the BATFET, not to mention the increased impedance from not driving the FET strongly, which would result in increased efficiency loss.

  • 0 in reply to Kedar Manishankar
    Guru 21930 points

    Hi kedar-san,

    Thank you for your kind response.
    >The BATDRV pin is only able to drive a battery MOSFET with Ciss lower than 5nF. 
    How did you calculate 5nF?

    >I was not able to find the 2nd mosfet option online, 
    I apologize to you for the lack of information.
    (TPCA8120)
    https://datasheetspdf.com/datasheet/TPCA8120.html
    (RS1E260AT)
    https://d1d2qsbl8m0m72.cloudfront.net/en/products/databook/datasheet/discrete/transistor/mosfet/rs1e260attb1-e.pdf

    >but the 1st option has 7820pF Ciss which would be too high.
    >You can also consider the MOSFET used on the EVM board: CSD25402Q3A (Ciss = 1380pF)
    Thank you for your information.
    However, the discharge current of the customer application is as large as 20A.
    Against this background, customer have to consider FETs with low Rds ON.

    Let me ask you another question.
    Customer is considering installing a resistor between the Pch FET gate and sauce to supplement the /BATD RV drive capability.
    As a result of cut and try, customers are considering installing 4.7kΩ.
    Do you have such a usage record?

    Best regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 24075 points

    Hi Yusuke-san,

     5nF is specified in the datasheet under section 9.4.1.1 System Voltage Regulation with Narrow VDC Architecture of datasheet.

     I believe adding the resistor from gate to source across the PFET will help enhance turn-off, and turn off the PFET if gate drive signal is not strong enough, but it wouldn't help much with enhancing the turn on ability of the BATDRV to turn on BATFET? 

  • 0 in reply to Kedar Manishankar
    Guru 21930 points

    Hi Kedar-san,

    Thank you for your kind support.

    〉I believe adding the resistor from gate to source across the PFET will help enhance turn-off,
    〉and turn off the PFET if gate drive signal is not strong enough, but it wouldn't help much with enhancing the turn on ability of the BATDRV to turn on BATFET? 

    Yes. Customers want to enhance turn-off.
    As a background, customers are testing battery removal.
    When the battery is removed, an issue occurs in which the BATFET has not been completely turned off for a certain period of time.
    Due to the issue, Vsys went down when the battery was removed.

    The issue could be avoided by installing a resistor between gate and sauce.
    Therefore, we are studying the resistor between gate and sauce in order to strengthen the power to turn off the BATFET.

    As a result of cut and try, customers are considering installing 4.7kΩ.
    Do you have such a usage record?

    Best regards,
    Yusuke

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 24075 points

    Hi Yusuke-san,

        Adding a resistor from gate to source is good to enhance turn-off. There shouldn't be any issues with this, and 4.7k or 1k should be more than enough. Keep me updated with results of cut-in test.