Issue observed ADC channel scan during free run mode

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Hi,

 

Presently I am using ATxMEGA32E5. Connected 8 analog channels using multiplexer intern connects to ADC channel using differential input ADC1 and ADC8.

Switching ADC channels using multiplexer for scanning the ADC inputs while in Free running mode. Input of ADC varying from 4 mv to 40 mv.

when I have the constant input in ADC channel by selecting multiplexer I see right ADC counts comes from ADC register.

As soon as I start multiplexing by having constant input fed all ADC channels. I don't get right ADC counts in registers. Datasheet of controller claims for  20us as settling time.

with this kind of hardware configuration holds good for 20us of settling time?

 

Note:  I get right ADC count when I provide the delay of 2 to 2.5 ms after the each multiplexer swithcing. Multiplexer selected is CD4097BMS.

ADC configured to 2 MHZ.

 

Thanks in advance.

 

 

 

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With free running mode you have this problem as a conversion may already be underway when you change the multiplexer. Solution: don't use free run mode or ignore one or more readings after you change the multiplexer.

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You can use SCAN register for scanning several inputs by Channel0.

Ozhan KD
Knowledge is POWER