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TPS3808: Pull up resistor

Hirotaka Matsumoto
Guru 27585 points
Part Number: TPS3808

Hi all

Would you mind if we ask TPS3808?

On the datasheet P12, there is the description "The pullup resistor should be no smaller than 10 kΩ as a result of the finite impedance of the RESET line."
If the pullup resistor is less than 10kohm(for example 5kohm), what kind of problem does it occur?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Genius 12630 points
    Hi Hirotaka,

    There are 2 things to consider:

    Functionality:
    As you decrease the pull-up resistor, the VOL (voltage when output is logic low during the fault condition) will be higher as the pull-up resistor decreases. If you decrease the pull-up resistor all the way to 1 ohm for example, the VOL will be close to the pull-up voltage even when the output is expected to be 0V.

    Device damage:
    As you decrease the pull-up resistor, the current through the /RESET pin increases during logic low condition. The device's internal MOSFET can only handle 5mA so the pull-up resistor needs to be large enough to keep the /RESET current below the abs max value of 5mA to prevent device damage.

    The /RESET current is calculated as follows:

    I_RESET = (Pull-up_voltage - VOL) / pull-up_resistor

    Please let me know if you have any more questions or if anything is unclear. Thanks!

    -Michael