SDAA162 July   2026 ADS125H18 , ISO7721 , ISO7730 , ISO7731 , SN6505B , SN74LVC1G17 , TUSB320 , TVS3301

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Design Overview and Measurement Performance (Normal Operation)
    1. 1.1 Design Overview
    2. 1.2 EMC Test Board Voltage Measurement Performance During Normal Operation
    3. 1.3 EMC Test Board Current Measurement Performance During Normal Operation
  5. 2EMC Test Board Circuit and PCB Layout Considerations
    1. 2.1 Circuit Design Considerations for EMC Compliance
      1. 2.1.1 High-Voltage Capacitors and Resistors on Every Input Connector Pin
      2. 2.1.2 TVS Diodes
      3. 2.1.3 Protecting the Current Shunt: PTC and Zener Diodes
      4. 2.1.4 Series Resistors on Digital Signals
      5. 2.1.5 Digital Isolation
      6. 2.1.6 Power Supply and Protection
      7. 2.1.7 High-Voltage Capacitors and Resistors for Discharging Path
    2. 2.2 PCB Layout Considerations for EMC Compliance
      1. 2.2.1 PCB Layer Stack-up and Ground Plane
      2. 2.2.2 Avoiding a Long Return Path
      3. 2.2.3 Avoiding 90-Degree Bends in PCB Traces
      4. 2.2.4 Using a Guard Ring to Isolate Interference Signals
      5. 2.2.5 Decoupling Capacitors
      6. 2.2.6 Differential Signal Routing
      7. 2.2.7 Stitching Vias
      8. 2.2.8 Layout for Isolation Barrier
      9. 2.2.9 Component Placement
  6. 3EMC Test System, Standards, and Results
    1. 3.1 EMC Test System
    2. 3.2 EMC Test Standards
    3. 3.3 EMC Test Results
      1. 3.3.1 Electrostatic Discharge (ESD)
      2. 3.3.2 Radiated Immunity (RI)
      3. 3.3.3 Electrical Fast Transients (EFT)
      4. 3.3.4 Surge Immunity (SI)
      5. 3.3.5 Conducted Immunity (CI)
  7. 4Schematic, PCB Layout and Bill of Materials
    1. 4.1 Schematic
    2. 4.2 PCB Layout
    3. 4.3 Bill of Materials (BOM)
  8. 5Summary
  9. 6References

1.2 EMC Test Board Voltage Measurement Performance During Normal Operation

Figure 1-3 shows a block diagram of the ADS125H18 measuring a 10V input signal. Note that no external components are required in this case because the ADS125H18 integrates a high-voltage resistor divider per channel such that the 10V signal can be measured directly by the ADC.

Voltage Input (±10V) Measurements Using the ADS125H18Figure 1-3 Voltage Input (±10V) Measurements Using the ADS125H18

The ADS125H18 on the EMC test board was programmed with the following settings to measure the circuit shown in Figure 1-3:

  • 12.5kSPS data rate
  • Sinc4 digital filter
  • AIN8/AIN9 differential analog inputs
  • Internal 2.5V reference
  • Internal 25.6MHz oscillator
  • Speed mode 3 (fMOD = 12.8MHz)

Figure 1-4 shows the actual ADS125H18 EMC test board with a 9V battery connected to the inputs to mimic a 10V process signal:

ADS125H18 EMC Test Board Measuring a 9V BatteryFigure 1-4 ADS125H18 EMC Test Board Measuring a 9V Battery

Calculate the ADS125H18 EMC test board performance by first measuring the actual input signal and reference voltage using a digital multimeter (DMM). These values were measured as follows:

  • VIN = 9.300V
  • VREF = 2.508V

Figure 1-5 shows the output from the ADS125H18 EVM graphical user interface (GUI) during the voltage measurement test:

Voltage Measurement Results from the ADS125H18 EMC Test Board GUIFigure 1-5 Voltage Measurement Results from the ADS125H18 EMC Test Board GUI

Use this information to determine the total unadjusted error (TUE) of these measurements using Equation 5:

Equation 1. TUE=VADC-VDMMVDMM×100

where:

  • VADC = Voltage measured by the ADC
  • VDMM = Voltage measured at the terminal block with a DMM

Equation 6 calculates the voltage measurement error using the average value of 9.278881V from Figure 1-5

Equation 2. TUE=9.278881V-9.300V9.300V×100=-0.228%

Use the actual measured VREF voltage to determine the TUE with the VREF error removed. Equation 7 calculates the scaling value assuming VREFIdeal = 2.5V and VREFMeasured = 2.508V:

Equation 3. Scaling Factor=VREFMeasuredVREFIdeal=2.508V2.5V=1.0032

Equation 8 calculates the voltage measurement error with the VREF error removed:

Equation 4. TUENo_VREF_Error=9.278881V-9.300V9.300V×100=0.04%

Ultimately, these results indicate that the ADS125H18 EMC test board is a high-performance system for process-level voltage measurements such as ±10V.