SBAU433 November   2025

 

  1.   1
  2.   Description
  3.   Get Started
  4.   Features
  5.   Applications
  6.   6
  7. 1Evaluation Module Overview
    1. 1.1 Introduction
    2. 1.2 Kit Contents
    3. 1.3 Specifications
    4. 1.4 Device Information
  8. 2Hardware
    1. 2.1 Analog Inputs
      1. 2.1.1 Differential Current Input Channels
      2. 2.1.2 Differential Voltage Inputs Channels
      3. 2.1.3 Combined Differential Current and Voltage Input Channels
      4. 2.1.4 Single-Ended Current Input Channels
    2. 2.2 ADC Connections and Decoupling
    3. 2.3 Digital Interface
    4. 2.4 Power Supplies
    5. 2.5 Voltage Reference
    6. 2.6 Clocking
    7. 2.7 Using the ADS125H18 EVM With an External Controller
  9. 3Software
    1. 3.1 Software Description
    2. 3.2 ADS125H18 GUI Installation
  10. 4Implementation Results
    1. 4.1 Hardware Connections
    2. 4.2 GUI Operation
      1. 4.2.1 ADC Capture Settings and Sequencer Configuration
      2. 4.2.2 EVM Register Settings
      3. 4.2.3 Time-Domain Display
      4. 4.2.4 Frequency-Domain Display
      5. 4.2.5 Histogram Display
  11. 5Hardware Design Files
    1. 5.1 Schematics
    2. 5.2 PCB Layouts
    3. 5.3 Bill of Materials (BOM)
  12. 6Additional Information
    1. 6.1 Trademarks

2.1.3 Combined Differential Current and Voltage Input Channels

Figure 2-3 shows the schematic for one input channel that, by default, measures differential voltage signals from -10V to +10V. However, the user can also configure this channel to measure differential current signals from -20mA to +20mA. An isolated switch selects between the two modes by connecting or disconnecting a PCB-mounted shunt between the input terminals. This channel enables differential voltage measurements by default such that the PCB-mounted shunt is removed from the circuit. An ADC GPIO pin controls the isolated switch and is toggled by the GUI. The current or voltage is then measured directly by the ADS125H18 without the need for external attenuation.

ADS125H18EVM-PDK Combined Differential Current and Voltage Input ChannelFigure 2-3 Combined Differential Current and Voltage Input Channel

Table 2-6 describes the function of each component in the combined differential current and voltage input channel schematic. Additionally, Table 2-6 references component designators specifically from Figure 2-3; however, the information in the table generally applies to all combined differential current and voltage input channels.

Table 2-4 Important Components (Combined Differential Current and Voltage Input Channels)

COMPONENT

FUNCTION

Terminal block (J12)

Apply one differential current or voltage signal per terminal block

TVS diode (U13 and U14)
  • Protection device that limits transient voltage into the ADC
  • The recommended component (TVS3301) offers bidirectional voltage suppression at a typical breakdown voltage of 37.5V

The TVS diodes are not installed by default on this channel

Isolated switch (K2)

  • Low-ohm (0.35Ω max) switch controlled by ADC GPIO3
  • Enable this switch in current mode and disable this switch in voltage mode
  • Both switches (K1 [not shown] and K2) are controlled by the same GPIO and are therefore always in the same mode
  • The default measurement mode is differential voltage

Shunt (R31)

Converts the current signal to a voltage to be read by the ADC

Zener diodes (D12 and D13)

Protection device that limits the current through the shunt in case of a sustained positive or negative overvoltage event

PTC fuse (F6)

Protection device whose resistance increases with temperature, thereby increasing the total circuit resistance. This increased resistance limits the current through the shunt in the case of a sustained overvoltage event

Filter components (R29, R35, C35, C37, and C43)

Provides additional input filtering if desired

The capacitors are not installed by default on this channel. The installed resistors are 0Ω

Figure 2-3 shows that the default input channel configuration is differential-ended. As a result, the EVM supports measurement of current and voltage inputs that are at different common-mode voltages. However, verify that the absolute voltage on any input pin does not exceed the values specified in the ADS125H18 datasheet.