JAJU874 September   2022 ADS1282-SP

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Rset, Rref, and Gain Calculation
      2. 2.2.2 Analog Multiplexer Effect
    3. 2.3 Highlighted Products
      1. 2.3.1 ADS1282-SP
      2. 2.3.2 LMP7704-SP
      3. 2.3.3 TPS7A4501-SP
      4.      16
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Software Requirements
    3. 3.3 Test Setup
    4. 3.4 Test Results
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 サポート・リソース
    4. 4.4 Trademarks
  10. 5About the Author

3.3 Test Setup

Figure 3-3 Lab Setup to Simulate Temperature Measurement

Figure 3-3 illustrates the block diagram of the lab setup for simulating temperature measurement. The purpose of this setup is to record RTD1 and RTD10's differential voltages. These two RTDs have the highest (High Vcm) and lowest (Low Vcm) common mode voltages, respectively. All RTDs are connected in series and current is biased by Rset. During data collection, Rset is set to three different values thus three sets of data are collected.

Following equations in Section 2.2.2, with IRTD­ set to 0.497 mA, 0.995 mA, and 1.49 mA, the Rset, Rref, Gain, and % positive FSR are calculated and illustrates in Table 3-1.

Table 3-1 Test Setup with Different IRTD
Setup 1 Setup 2 Setup 3
IRTD [mA] 0.497 0.995 1.49
Rset [Ω] 4.5k 750 500
Rref [Ω] 4.76k 2.18k 1.1k
Gain 16 8 4
% positive FSR used 90.8% 99.1% 98.2%

Figure 3-4 illustrates how (circled in red) to modify PGA gain, configure mux, and read the returned codes on GUI.

GUID-20220829-SS0I-4S8N-FKK7-4THNTQZGZ6CF-low.png Figure 3-4 ADS1282EVM-PDK GUI Setting

The ADS1282EVM-PDK GUI returns values with 2 formats, codes and voltage. The codes is a 31 bits data and is used to calculate RTD resistance with the following equation, and the calculated value is compared with the actual resistor value for error analysis.

Equation 5. RTD Resistance= CodesGain×231×Rref