SDAA088 September   2025 AMC0100R , AMC0311R , AMC0311R-Q1 , AMC0330D , AMC0330R , AMC0330R-Q1 , AMC0330S , AMC0336

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Pairing Ratiometric Output Isolation Amplifier With ADC
    1. 2.1 Test Setup
    2. 2.2 REFIN Voltage Tracking
    3. 2.3 Ratiometric Configuration Noise Rejection
    4. 2.4 Spurious-Free Dynamic Range
    5. 2.5 Transient Response of REFIN to VOUT
    6. 2.6 Transfer Function of REFIN to VOUT
  6. 3Summary
  7. 4References

3 Summary

This application report demonstrates the in-system performance of the ratiometric output isolated amplifier, highlighting the ability to reject low-frequency reference voltage variations. In many scenarios, the designer can completely remove the precise voltage reference for the ADC and instead use the integrated voltage reference or the digital power rail that supplies the microcontroller. While the ratiometric configuration offers benefits at lower frequencies, its effectiveness is limited at higher frequencies due to delays and phase-shifts in the filter stages, which prevent the output signal VOUT from timely tracking the reference voltage VREF. Nonetheless, assembling the CREFIN capacitor is recommended in all cases, as this effectively prevents higher-frequency noise from coupling to the REFIN pin.