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MAX11254 Conversion Issues

Category: Hardware
Product Number: MAX11254

Hi! 

I am currently developing product which uses MAX11254 ADC.

Project requires sampling two channels of ADC precisely each 200 us which is 10kSps total sampling rate. PGA is enabled.

Each 200 us new conversion should be started and results of old conversion should be read by microcontroller.

1. Therefore I decided using ADC in sequencer mode 2 with two channels(CH0 and CH1). In theory this should be working fine because with maximum data rate, conversion only, single conversion should last approximately 85us. So two conversions should last 170 us in total. And they do, but sequencer mode 2 quits to sleep mode after conversion. And quitting sleep mode can last up to 45us! Which obviously exceeds timing constraints. I came up with workaround- I setup sequencer mode 2 with 3 channels and the third one is just a dummy conversion which is interrupted by new conversion command in the middle. This system fulfills timing constraints, but using this setup leads to another Issue.

2. I observed that conversion of open channel (P and N wires not connected), which is in my case this dummy channel affects measurement on loaded channels. It creates some additional offset. Loaded channels don't affect each other. The solution I found is shorting P and N ports of the channel. This reduces shifted offset problem to minimum. But again this is sort of workaround.

Do you know any other, more straightforward solution to the problems.  The best solution for problem no. 1 would be just preventing ADC from going to sleep after finishing channel sequence. Problem no. 2 seems to be more analog-related issue (some internal capacity?).

Thanks in advance for any help Slight smile

Regards, 

Piotr

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