2 System Overview

This reference design accurately measures AC voltage and current inputs using a precision 16-bit successive approximation (SAR) analog-to-digital converter (ADC) over a wide input range covering protection and measurement applications (including sampling requirements as per IEC 61850-9-2), simplifying system design and improving trip time performance and reliability. Two approaches for designing of AIM have been shown in this reference design. The first approach is using a 16-channel 16-bit SAR dual simultaneous sampling ADC. The second approach is using two 8-channel 16-bit ADCs connected together to increase the number of analog input channels to 16 using daisy chain mode or dual SDO output mode with the control input signals connected together and driven by common pins. The AIM is isolated from the host processor using a digital isolator with an integrated power converter. A complete AC AIM can be designed using only TI products, optimizing system cost and size. The alarm feature of ADS8688A identifies the AC analog input faults on a sample basis for faster fault detection. The ADS8688A ADC has an additional auxiliary channel to diagnose the supply output of the digital isolator.