I am wondering how R45 and C34 were selected for the speed reference circuit in TIDA-00774.
1) Is the selection designed to filter noise caused by the MOSFET switching? The cutoff frequency calculated based on R45 = 10K and C34=0.1 uF is about 150 Hz. The switching frequency in this application is 20 KHz.
2) or is the selection designed to filter noise to MCU MSP430F5132IDA? The time constant calculated based on R45 = 10K and C34=0.1 uF is about 1 ms. Based on the MSP430F5132IDA datasheet, page 40, the sample time, ts is 1 ~ 3 us. The RC time constant should be less than the sample time. But calculated RC time constant is about 1000 times higher.
3) or other considerations?
I will appreciate you could provide the reasoning for this selection? I see other design applications using much lower R value (say 100 ohms instead of 10k) and much lower C value (say 3300 pF), both are several orders smaller.