Other Parts Discussed in Thread: INA240, BOOSTXL-3PHGANINV
Hi,
I am using the INA240A1 (gain of 20) in a design, after the INA240 I put a 20 kHz nyquist filter to limit noise going into my ADC sampling at 40 kHz. Unfortunately, this causes the noise induced by the PWM switching to settle more slowly which is not desireable but makes sense.
To not degrade the INA240A settling time, is it OK to move the nyquist filter to the input of the INA240? I understand about the series resistance issues with gain but do not have a feel for negative effects by adding a capacitor across the differential inputs and using this capacitance in conjunction with the input series resistance to form a Nyquist filter. I would not be adding capacitors from the inputs to ground, just across the input.
In the BOOSTXL-3PhGaNInv example schematic, I see a 1500 pF cap has been added here. Is there a limit on how big this capacitor can be? I am looking at maybe placing 100's of nF. Is this OK or will it mess up the common mode rejection or other critical design characteristics?
Just curious in this same schematic an RC (20 ohms, 2200 pF) filter is added after the INA240 with a cut-off of 3.6 MHz. Is this filter important?
Thank you,
Jennifer