there is a voltage on the input ADC

Dear all,

I'm having a problem with the ADC input of the TMS320F28069.

When I turn on the ADC clock, in ADC input pins there are about 900mV.

This voltage adds to the voltage of my signal, so the ADC-result value don't start from 0 to 4096, but it starts from (800-900) to full scale.

If I turn off the ADC clock signal, these voltages there aren't.

Can you help me please.

Thank you for your kindness.