TCAN4551-Q1: Cancel weak pull up at SCLK pin

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 I_IL ≤ 100 µA across process, voltage, and temperature. We would want a resistor that can keep the SCK voltage below V_IL = 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 V_IL ≤ I_ILR

R ≤ V_IL / I_IL

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