Question about driving Mc9SXS128 ADC pin

[yonghaihou]

I want to use PAD pin to sample temperature, can simple voltage dividor network（showed as below figure) with  series-connection of sense resistor(vary from 1.5K to 330K as the temperature change) pulled down to GND and a 10K resistor pulled up to 5V drive the ADC pin? Is the source resistor ok for MCS9S12XS128?

Thanks!

[martynek]

Hi

There is no extra voltage divider.

The voltage is sampled directly from your voltage divider.

I thing no Op-Amp Buffer is needed.

Also, the RC circuit seems to be stable, since the capacitance is greater than (2^N) * 6pF.

You may find more information here:

http://www.nxp.com/assets/documents/data/en/application-notes/AN2429.pdf

Regards

Daniel

[yonghaihou]

Hi, Dan Martynek.

It's all clear. Thank you very much!

[martynek]

Hi

I can’t see any problem with that.

[yonghaihou]

Thank you , Dan Martynek.

But I'm not sure about the input resistor of the ATD pin, typically 5Ko, at most 15Ko. Does it mean if the source resister is 10Ko, the voltage sampled by the internal ADC will be approximately half of source voltage? Is OPAMP voltage following curcuit necessary to reduce the source resistor?