Other Parts Discussed in Thread: ADS8691, ADS8695,
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Hello Liu Chih,
Thanks to post this query on E2E forum, actually we don’t understand your question very clearly, but following are important information about ADS8699:
Because of his internal integrated ADC driver, your external circuit will not be critical to settle the signal on sampling capacitor of internal 18-bit ADC.
Thanks and regards
Thanks For your answer.
I still do not understand if the LPF 15K HZ BW would limit the ADC BW or no?
For example I put a ideal input signal it step from 0V to 10.24V(unipolar full scale).
If no LPF I think ads8699 can get code 3FFFFH after 10us after the step.
But with this low pass filter does it need to take more time or no (to get the full scale code 3FFFFH)?
If it need how long ? and how long to get 0.01% code (10.238976V)?
Hello Liu Chih,
The LPF filter is different from switched-capacitor circuit inside SAR ADC. To guarantee the performance without any degradation to the SAR ADC with switched-capacitor input structure, the ADC driver will have to charge ADC's internal sampling capacitor to input signal voltage during during acquisition phase and have to make sure the settling error on sampling capacitor is less than 1LSB, this charging process has to be finished before conversion phase of ADC starts and the internal switch is open. The signal acquisition is critical but ADS8699 has an integrated ADC driver behind 2nd order low pass filter which will execute this function in 5us acquisition time and meet this 18-bit ADC's settling requirement. The 15KHz BW LPF limits the input signal frequency.