SBAU126E may   2007  – june 2023 ADS1158 , ADS1258

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1ADS1258EVM Overview
    1. 1.1 ADS1258EVM Kit
    2. 1.2 ADS1258EVM
  5. 2Getting Started With the ADS1258EVM
  6. 3Analog Interface
    1. 3.1 Analog Input Options
    2. 3.2 ADC Connections and Decoupling
    3. 3.3 Configurable Multiplexer Loop
      1. 3.3.1 Measuring Single-Ended Inputs Using a Pseudo-Differential Configuration
    4. 3.4 Clocking
    5. 3.5 Voltage Reference
  7. 4Digital Interface
    1. 4.1 GPIO
  8. 5Power Supplies
  9. 6Software Installation
  10. 7EVM Operation and GUI
    1. 7.1 Connecting the Hardware
    2. 7.2 EVM GUI Global Settings for ADC Control
    3. 7.3 Time-Domain Display
    4. 7.4 Frequency-Domain Display
    5. 7.5 Histogram Display
  11. 8Bill of Materials, Layout, and Schematics
    1. 8.1 Bill of Materials
    2. 8.2 EVM PCB Layout
    3. 8.3 Schematics
  12. 9Revision History

Configurable Multiplexer Loop

The ADS1258 multiplexer has optional differential output connections (MUXOUTx) that enable a single signal-conditioning circuit to be used for all analog inputs. The default signal conditioning circuit is a differential unity-gain buffer (OPA2320) between each MUXOUTx and ADCINx pin. A low-pass filter is connected to the output of the buffer. As shown in Figure 3-3, capacitor C20 is used to bypass the ADC sampling currents and resistors R25 and R35 are used to isolate the op-amp outputs from the filter capacitor.

GUID-20221026-SS0I-4H9X-BKX7-ZP0P1V8QCRR3-low.svgFigure 3-3 ADS1258EVM Configurable Multiplexer Loop With a Signal-Conditioning Circuit

The signal-conditioning circuit shown in Figure 3-3 can also be configured into a differential-input, differential-output gain stage by changing resistors R24, R30, and R31 as per Equation 1.

Equation 1. G = 1 + 2 × (R24) / R30

Importantly, Equation 1 assumes that R31 = R24.

As an example, replacing R24 and R31 with 10-kΩ resistors and R30 with a 2.2-kΩ resistor creates a gain of 10 V/V between the MUXOUTx and ADCINx pins. Choose R24, R30, and R31 to be size 0603 resistors with a tolerance ≤0.1% to maintain system accuracy.

Enable the multiplexer loop by setting BYPAS = 1 in the CONFIG0 register. To bypass the multiplexer loop, set BYPAS = 0. One important caveat to the multiplexer bypass option is that the signal-conditioning circuit is only disconnected from the ADCINx pins. In other words, the signal-conditioning circuit is still connected to the MUXOUTx pins regardless of the state of the BYPAS bit.