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TCAN4551-Q1: Cancel weak pull up at SCLK pin

Part Number: TCAN4551-Q1

Hello team,

According to the datasheet, there is weak pull up on the SCLK pin.
However, I want SCLK to be LOW, when CPU start up.

What is the resistor value I need to pull down in order to cancel the weak pull up?

Best Regards,
Kei Kuwahara

  • Kei,

    The answer somewhat depends on your VIO voltage in your application, because the thresholds are based upon VIO.

    The strongest possible pull-up from SCK is given as IIL ≤ 100 µA across process, voltage, and temperature. We would want a resistor that can keep the SCK voltage below VIL = 0.3*VIO. If we assume a VIO = 3.3 V, then this would be a low-level input threshold voltage of 0.99 V ≈ 1 V.

    We can use V = IR as VIL ≤ IILR

    R ≤ VIL / IIL

    R ≤ (1 V) / (100 µA)

    R ≤ 10 kΩ

    So, I would say less than 10 kΩ would be strong enough. To determine the maximum strength, this would depend on your SCK source.

    Best,

    Danny

  • Hi Danny-san,

    Thank you for the detailed answer!

    Best Regards,
    Kei Kuwahara