SBAA507 March   2021 ADS8578S , ADS8584S , ADS8586S , ADS8588H , ADS8588S , ADS8598H , ADS8598S , ADS8661 , ADS8664 , ADS8665 , ADS8668 , ADS8671 , ADS8674 , ADS8675 , ADS8678 , ADS8681 , ADS8684 , ADS8684A , ADS8685 , ADS8688 , ADS8688A , ADS8688AT , ADS8689 , ADS8691 , ADS8694 , ADS8695 , ADS8698 , ADS8699 , OPA2990 , OPA4990 , OPA990

 

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  2.   Design Description
  3.   Specifications
  4.   Design Notes
  5.   Component Selection
  6.   DC Transfer Characteristics
  7.   Simulation Verification for Floating Input
  8.   AC Transfer Characteristics
  9.   Noise Simulation
  10.   Stability Simulation
  11.   Design References
  12.   Design Featured Devices

Design Description

This circuit shows a solution to detect if the ADS8681 successive approximation register (SAR) analog-to-digital converter (ADC) input is floating. The ADS8681 device features a significant amount of signal chain integration, including high resistive input impedance, a programmable gain amplifier (PGA), and an ADC input driver. These features eliminate the requirement for driving the ADC inputs with a high-bandwidth amplifier. Therefore, a low-bandwidth, low-cost amplifier in a non-inverting unity gain configuration can be used in a solution for detecting a floating input. This solution has a minimal impact on the system performance metrics including signal-to-noise ratio (SNR) and total harmonic distortion (THD). This circuit is useful in end equipment such as: Analog input module, Servo drive functional safety module, Motor drives, and Factory automation and control.

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