DRV401-Q1: DRV401 -how to choose the value of R3 R4 C3 C4

Hello Jie,

I will quote the datasheet on this as will depend on the magnetic probe.

"R3 and R4, together with C3 and C4, form a network
that reduces the remaining probe oscillator ripple in
the output signal. The component values depend
on the sensor type and are tailored for best results.
This network is not required for normal operation."

The frequency will vary depending on the probe used. This is due to the probe saturating can vary from probe to probe.

"The probe core reaches saturation at a current of typically
28mA (see Figure 2a). The comparator is connected to
VREF by approximately 0.5V. A current comparator detects
the saturation and inverts the excitation voltage polarity,
causing the probe circuit to oscillate in a frequency range
of 250kHz to 550kHz. The oscillating frequency is a
function of the magnetic properties of the probe core and
its coil."

Have you attempted your probe and seen its frequency response? I would measure that frequency at the normal operating contrition as the frequency can drift a little do to the magnetic probe properties drifting.