AD7794 intead of ADUCM360

Question

Hello 
 I want use AD7794 instead of ADuCM360 in CN-0359 Circuit Note. 
 But I am confused about which pin configuration I should use. 
 I have indicaetd the ADC pins in the picture. 
 What should ADC[3:0] pins pole configuration be? 
 For example : ADC0, ADC1, ADC2, ADC3 respectively (+)(-)(+)(-) 
 What is the proper congfiguration for these pins?

FormerMember · Accepted Answer

Hi cevdet29, 
 Each of the ADC channels being sent to ADuCM360 in the CN0359 are single-ended inputs. So you'll want to send each input (ADC[0:3]) to the AIN[0:3] (+) inputs and ground the AIN[0:3] (-) inputs of the AD7794 within this application. 
 You'll also need to ensure that you have an excitation current available for the RTD input on the AD7794 that is available. So you might need to ensure the RTD section of the design is set properly and then set the rest of the channels to read the analog voltages. 
 Hope that helps 
 Brandon)

rogueC · Answer

Hi cevdet29, 
 The ADuCM360 has pseudo differential capability and can accept the 4 signals as either single ended or differential inputs. The AD7794 has fully differential inputs and what Brandon suggests will be enough for your application. But, you can also connect them as a differential signals with ADC3 and ADC2 connected to a positive and negative differential input, respectively (e.g. ADC3 to AIN1(+) and ADC2 to AIN1(-) ). In this way, you use only two differential input pairs. 
 You do have to set the register settings for the excitation currents in AIN5 to use the RTD. 
 Also, the ADC signal inputs from the CN0359 are at 1.65V +/- 1.65 V. You will need to use an external reference of 3.3V to fully capture the signal. The ADuCM360 accomplishes this through an AVDD/IOVDD of 3.3V. 
 I would also like to suggest you use the AD7124-4. It has pseudo differential operation and can use 3.3V reference. It also is a 24-bit sigma-delta ADC and is for low power applications which is similar to the AD7794. 
 Anyway, the AD7794 will still work for your application. Hope this helps, 
 Nikko

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AD7794 intead of ADUCM360