TMS320F28034: ADC pin internal resistance

Hi Jordan,

That really depends on the source impedance of the signal that the customer is feeding to the buffer.  If the source impedance is low, it is likely that it can be connected directly to the ADC pins as the source impedance might not be enough to impact the input network.  There might be a reason why the customer placed the buffer in the first place and that may be to compensate for the signal source impedance.

If there is impedance mismatch on the signal source and ADC input network, this will disrupt settling time, thus affecting the accuracy of conversion.  This should be considered by the customer in making that decision.

Regards,

Joseph 

Joseph,

The impedance could be high or low. This is why customer is asking the ADC internal impedance. They need the value to very if a buffer is needed.

Thanks a lot.

br, Jordan

Hi Jordan,

Please refer to Fig 6-20 of the device data sheet for the Input Impedance model (embedded here).  This should provide guidance for the application if the input buffer is needed or not depending on the source impedance.

Best regards,

Joseph

Joseph,

This figure, we already saw.

Actually, customer would like to know the equivalent resistance, from ADC pin to internal circuit. In this way, they can evaluate if the buffer can be saved.

Thanks a lot.

Br, Jordan

Hi Jordan,

      Not sure what else the customer is looking for.  The Cp, Ron and Ch are the equivalent resistance and capacitance of the internal ADC module.  If i am missing something, please elaborate further.

Thanks,

Joseph