AD7176-2

Hi ,

 

I have planned to use AD7176-2 ADC in our project to read thermocouple, thermistor, RTD , Voltage , Current and strain gauge sensors. I am finding it hard to fix what is the conversion time and settling time.

 

I will be using one channel with output datarate @ 10ksps and Sinc5+sinc1 filter settings. In "Table 18. AD7176-2 Output Data Rate (ODR)". It mentions that @ 10KSPS Settling time is 100uSec. But it doesnt mentions about the conversion rate.

Please let us know what is Settling time? Is it applicable for ever conversion as I will be using external mux to provide input to the ADC and what is the conversion time. I have 16 channels to be converted.

Also I would like to know whether to use an continues conversion mode or single conversion mode. As the device is a battery operated I want an optimal solutions.

Regards,

ChiranjeeviM

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  • 0
    •  Analog Employees 
    on Jun 20, 2013 1:24 PM

    Hi Chiranjeevi,

    100us will be all it takes to get a conversion sample.

    So switch -- start conversion -- 100us -- DOUT/nRDY will be pulled low and you can get your conversion data.

    For your system, in case you didn't notice there is a "MUX to GPIO" feature in AD7176-2(search MUX_IO in the datasheet) which allows you to sync each switching of the external MUX with the start of conversion.

    However there are only 4 internal channels in AD7176-2.

    My suggestion is:

          Wire the GPIO pins to lower 2-bits of the 16-chn MUX decoder, control the higher 2-bits with you MCU;

         Enable MUX_IO;

         Enable all four channels, use same setting for"CH_SELx" on each channel, also same setting for "AINPOSx" and "AINNEGx".

    Now the loop:

         1.Set the higher 2-bits of MUX decoder to "00";

         2.Set ADC to Single Conversion;

         3.Watch the DOUT/nRDY line and read back conversion when it's ready;

        DRDY will happen once every 100us till all four channel is converted, then ADC puts itself to standby mode.

         4. Set higher 2-bits of MUX decoder to "01", repeat from step 2 and 3 to convert next 4-channels;

         ......

    There is also a delay that can be programmed ("DELAY" bits in MODE register) so the ADC will wait a short time before start of each conversion allowing external circuit to settle after switching. You can look into that.

    Regards

    Cheng

Reply
  • 0
    •  Analog Employees 
    on Jun 20, 2013 1:24 PM

    Hi Chiranjeevi,

    100us will be all it takes to get a conversion sample.

    So switch -- start conversion -- 100us -- DOUT/nRDY will be pulled low and you can get your conversion data.

    For your system, in case you didn't notice there is a "MUX to GPIO" feature in AD7176-2(search MUX_IO in the datasheet) which allows you to sync each switching of the external MUX with the start of conversion.

    However there are only 4 internal channels in AD7176-2.

    My suggestion is:

          Wire the GPIO pins to lower 2-bits of the 16-chn MUX decoder, control the higher 2-bits with you MCU;

         Enable MUX_IO;

         Enable all four channels, use same setting for"CH_SELx" on each channel, also same setting for "AINPOSx" and "AINNEGx".

    Now the loop:

         1.Set the higher 2-bits of MUX decoder to "00";

         2.Set ADC to Single Conversion;

         3.Watch the DOUT/nRDY line and read back conversion when it's ready;

        DRDY will happen once every 100us till all four channel is converted, then ADC puts itself to standby mode.

         4. Set higher 2-bits of MUX decoder to "01", repeat from step 2 and 3 to convert next 4-channels;

         ......

    There is also a delay that can be programmed ("DELAY" bits in MODE register) so the ADC will wait a short time before start of each conversion allowing external circuit to settle after switching. You can look into that.

    Regards

    Cheng

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