Greetings all, I am working with the gate driver STDRIVE101 to drive a BLDC motor. For the current sensing opamps, the value of the filter capacitor was calculated based on the cut-off frequency, my question is, does this cutoff frequency depend on Fsw?

[HIbra.1]

Fsw is the switching frequency of the Mosfets, i am asking if this value should be considered when calculating the filter capacitor value or not

[Cristiana SCARAMEL]

Hello @HIbra.1​ and welcome to the ST Community.

Are you using our EVALSTDRIVE101 demonstration board or a custom board?

In the second case, could you share the schematic?

To set the cut-off filter frequency you have to consider two points:

• the target is to filter ringing on PWM rising edges
• the filtering effect slows down the PWM edge (therefore waiting more time to sample)

You must find a tradeoff between these aspects.

In general a cut-off frequency of the order of 1 MHz can be enough.

Moreover take into account that the OpAmp has its own limited bandwidth that acts as filter itself

(e.g. GBWP = 10 MHz, setting a gain of 10 --> BW = 1 MHz).

I hope this post can help you; if so, consider to mark it as best answer by clicking the label "Select as Best".

[Cristiana SCARAMEL]

Hello @HIbra.1​ there are updates from you?