Question I will be running the AD7864 from its internal clock, i.e. #INT/EXT CLK pin pulled low. Is it OK to leave the unused CLKIN pin floating or do I need to pull it low also. Answer Yes its OK to leave it floating.

AD7864: Chip Select Inputs

Question Other inputs on the AD7864 (#STBY, #WR and Chip Select Inputs SL1 & SL2) are going to be pulled high via pull-up resistors. Do these lines need to be pulled high to the +3.3V supply or to the main +5V supply (DVDD)? Answer These can be pulled to the 5V supply, through pullups.

AD7864: Pin Connections

Question Q1.: I will only be using two of the four analog inputs on the AD7864. Do I need to pull the two unused inputs low or is this done internally by the AD7864. Q.: 2 I will be connecting an external reference (AD780) to the AD7864. The external reference (AD780) chip has a 2.5V and a 3V option. Will the accuracy and dynamic range of the AD7864 be improved by using the 3V reference option. Answer Question 1: If not used, inputs should be connected together to ground. Question 2: The part is not designed to be used with a 3V reference. Anything other than a 2.5V reference will result the transfer function of the ADC generating errors. So I can only recommend to use a 2.5V reference or the internal reference.

Q Customer wanted to know the sensitivity level for AD7864, ESD data for this pn is not available on the reliability report A The ESD we have for the HBM of the AD7864-2 is 500V

Q What is the meaning of the absolute input voltage A The AD7864 is a replacement for the TI part ADS8321 so the product line has put the “Absolute Input Voltage” spec in the general specifications section of the datasheet (as in the ADS8321 datasheet) rather than in the "Absolute Maximum Ratings" section as is the ADI standard. See the following clarification provided by the AD7684 applications engineer: The "Absolute Input Voltage" under the specs table is simply a copy of what the major competitor TI is doing. This is traditionally not the ADI standard. "Absolute Maximum Ratings" are in their own section and you should refer the customer to this section. The operating input range on IN+ for all small package PulSAR ADCs is (AGND - 0.1)V to (Vref + 0.1)V. For single ended ADC, the operating input range on IN- is (AGND - 0.1)V to (AGND + 0.1)V. For differential input ADC, the operating input range on IN- is (AGND - 0.1)V to (Vref + 0.1)V. For the absolute max on these pins, refer to the "Absolute Maximum Ratings" section in the datasheet. In any event, all small package PulSAR ADC will be VDD + 0.3V, GND - 0.3V since there is an ESD structure on VDD and AGND on all of our ADCs inputs. The common mode input range for IN+ and IN- on the differential input ADCs is also (Vref/2 - 0.1) to (Vref + 0.1)V. Operating beyond the common mode operating point, introduces non linearity's. You cannot tie IN- to GND and swing IN+ from 0 to Vref on these ADCs with differential inputs.