What value resistor is recommended to place in series with ADC input as part of low bandpass filter?

[injunear1]

Somewhere I read that if noise is a possibility on the input of an ADC channel, it is a good idea to place an RC filter between the analog source and the MCU input.

I am using the KL25Z Freedom board. I think I read that there should be a .01 cap to ground and a (possibly?) 50 ohm or less resistor in series with the input.

Is this mentioned in the Freescale literature anywhere, and, if so, what values are recommended? Also, how might a 33 ohm resistor, for instance, affect the ADC timing?

Thank you.

[Paul_Tian · Accepted solution]

Hi, Injunear

In datasheet, there is no parameter lists. Because this depends application condition. As normal, analog inputs should also have low pass filters.  Fast sample times will require smaller capacitor values and source impedances than slow sample times. Higher resolution inputs may require smaller capacitor values and source impedances than lower resolution inputs.

Hope my reply can help you.

Best Regards

Paul