SPRACV0A February   2021  – March 2023 TMS320F2800132 , TMS320F2800132 , TMS320F2800133 , TMS320F2800133 , TMS320F2800135 , TMS320F2800135 , TMS320F2800137 , TMS320F2800137 , TMS320F2800152-Q1 , TMS320F2800152-Q1 , TMS320F2800153-Q1 , TMS320F2800153-Q1 , TMS320F2800154-Q1 , TMS320F2800154-Q1 , TMS320F2800155 , TMS320F2800155 , TMS320F2800155-Q1 , TMS320F2800155-Q1 , TMS320F2800156-Q1 , TMS320F2800156-Q1 , TMS320F2800157 , TMS320F2800157 , TMS320F2800157-Q1 , TMS320F2800157-Q1 , TMS320F280021 , TMS320F280021 , TMS320F280021-Q1 , TMS320F280021-Q1 , TMS320F280023 , TMS320F280023 , TMS320F280023-Q1 , TMS320F280023-Q1 , TMS320F280023C , TMS320F280023C , TMS320F280025 , TMS320F280025 , TMS320F280025-Q1 , TMS320F280025-Q1 , TMS320F280025C , TMS320F280025C , TMS320F280025C-Q1 , TMS320F280025C-Q1 , TMS320F280033 , TMS320F280033 , TMS320F280034 , TMS320F280034 , TMS320F280034-Q1 , TMS320F280034-Q1 , TMS320F280036-Q1 , TMS320F280036-Q1 , TMS320F280036C-Q1 , TMS320F280036C-Q1 , TMS320F280037 , TMS320F280037 , TMS320F280037-Q1 , TMS320F280037-Q1 , TMS320F280037C , TMS320F280037C , TMS320F280037C-Q1 , TMS320F280037C-Q1 , TMS320F280038-Q1 , TMS320F280038-Q1 , TMS320F280038C-Q1 , TMS320F280038C-Q1 , TMS320F280039 , TMS320F280039 , TMS320F280039-Q1 , TMS320F280039-Q1 , TMS320F280039C , TMS320F280039C , TMS320F280039C-Q1 , TMS320F280039C-Q1 , TMS320F280040-Q1 , TMS320F280040-Q1 , TMS320F280040C-Q1 , TMS320F280040C-Q1 , TMS320F280041 , TMS320F280041 , TMS320F280041-Q1 , TMS320F280041-Q1 , TMS320F280041C , TMS320F280041C , TMS320F280041C-Q1 , TMS320F280041C-Q1 , TMS320F280045 , TMS320F280045 , TMS320F280048-Q1 , TMS320F280048-Q1 , TMS320F280048C-Q1 , TMS320F280048C-Q1 , TMS320F280049 , TMS320F280049 , TMS320F280049-Q1 , TMS320F280049-Q1 , TMS320F280049C , TMS320F280049C , TMS320F280049C-Q1 , TMS320F280049C-Q1 , TMS320F28075 , TMS320F28075 , TMS320F28075-Q1 , TMS320F28075-Q1 , TMS320F28076 , TMS320F28076 , TMS320F28374D , TMS320F28374D , TMS320F28374S , TMS320F28374S , TMS320F28375D , TMS320F28375D , TMS320F28375S , TMS320F28375S , TMS320F28375S-Q1 , TMS320F28375S-Q1 , TMS320F28376D , TMS320F28376D , TMS320F28376S , TMS320F28376S , TMS320F28377D , TMS320F28377D , TMS320F28377D-EP , TMS320F28377D-EP , TMS320F28377D-Q1 , TMS320F28377D-Q1 , TMS320F28377S , TMS320F28377S , TMS320F28377S-Q1 , TMS320F28377S-Q1 , TMS320F28378D , TMS320F28378D , TMS320F28378S , TMS320F28378S , TMS320F28379D , TMS320F28379D , TMS320F28379D-Q1 , TMS320F28379D-Q1 , TMS320F28379S , TMS320F28379S , TMS320F28384D , TMS320F28384D , TMS320F28384D-Q1 , TMS320F28384D-Q1 , TMS320F28384S , TMS320F28384S , TMS320F28384S-Q1 , TMS320F28384S-Q1 , TMS320F28386D , TMS320F28386D , TMS320F28386D-Q1 , TMS320F28386D-Q1 , TMS320F28386S , TMS320F28386S , TMS320F28386S-Q1 , TMS320F28386S-Q1 , TMS320F28388D , TMS320F28388D , TMS320F28388S , TMS320F28388S , TMS320F28P550SJ , TMS320F28P550SJ , TMS320F28P559SJ-Q1 , TMS320F28P559SJ-Q1 , TMS320F28P650DH , TMS320F28P650DH , TMS320F28P650DK , TMS320F28P650DK , TMS320F28P650SH , TMS320F28P650SH , TMS320F28P650SK , TMS320F28P650SK , TMS320F28P659DK-Q1 , TMS320F28P659DK-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
    1. 1.1 Resources
      1. 1.1.1 TINA-TI SPICE-Based Analog Simulation Program
      2. 1.1.2 PSPICE for TI Design and Simulation Tool
      3. 1.1.3 Application Report: ADC Input Circuit Evaluation for C2000 MCUs
      4. 1.1.4 TI Precision Labs - SAR ADC Input Driver Design Series
      5. 1.1.5 Analog Engineer's Calculator
      6. 1.1.6 TI Precision Labs - Op Amps: Stability Series
        1. 1.1.6.1 Related Application Reports
      7. 1.1.7 TINA-TI ADC Input Models
  4. 2Charge-Sharing Concept
    1. 2.1 Traditional High-Speed ADC Driving Circuits
    2. 2.2 Increased Cs in High-Speed ADC Driving Circuits
    3. 2.3 Very Large Cs in ADC Driving Circuits
    4. 2.4 Charge-Sharing Operation
    5. 2.5 Sample Rate and Source Impedance vs. Tracking Error
    6. 2.6 Analytical Solution to Tracking Error
    7. 2.7 Charge-Sharing in Multiplexed ADCs
    8. 2.8 Charge-Sharing Circuit Advantages
    9. 2.9 Charge-Sharing Circuit Disadvantages
  5. 3Charge Sharing Design Flow
    1. 3.1 Gather Required Information
    2. 3.2 Size Cs
    3. 3.3 Verify Sample Rate, Source Impedance, and Bandwidth
    4. 3.4 Simulate Circuit Settling Performance
    5. 3.5 Input Design Worksheet
  6. 4Charge-Sharing Circuit Simulation Methods
    1. 4.1 Simulation Components
      1. 4.1.1 Vin
      2. 4.1.2 Voa , Voa_SS, and Verror
      3. 4.1.3 Rs, Cs, and Vcont
      4. 4.1.4 Ch, Ron, and Cp
      5. 4.1.5 S+H Switch, Discharge Switch, tacq, and tdis
    2. 4.2 Configure the Simulation Parameters
    3. 4.3 Simulating Op-amp Steady-State Voltage
    4. 4.4 Measure the Settling Error
    5. 4.5 Sweeping Source Resistance
  7. 5Example Circuit Designs
    1. 5.1 Example 1: Determining Maximum Sample Rate
      1. 5.1.1 Example 1: Analysis
      2. 5.1.2 Example 1: Simulation
      3. 5.1.3 Example 1: Worksheet
    2. 5.2 Example 2: Adding an Op-amp
      1. 5.2.1 Example 2: Analysis
      2. 5.2.2 Example 2: Simulation
      3. 5.2.3 Example 2: Worksheet
    3. 5.3 Example 3: Reduced Settling Target
      1. 5.3.1 Example 3: Analysis
      2. 5.3.2 Example 3: Simulation
      3. 5.3.3 Example 3: Worksheet
    4. 5.4 Example 4: Voltage Divider
      1. 5.4.1 Example 4: Analysis
      2. 5.4.2 Example 4: Simulation
      3. 5.4.3 Example 4: Worksheet
  8. 6Summary
  9.   A Appendix: ADC Input Settling Motivation
    1.     A.1 Mechanism of ADC Input Settling
    2.     A.2 Symptoms of Inadequate Settling
      1.      A.2.1 Distortion
      2.      A.2.2 Memory Cross-Talk
      3.      A.2.3 Accuracy
      4.      A.2.4 C2000 ADC Architecture
  10.   References
  11.   Revision History

2.7 Charge-Sharing in Multiplexed ADCs

Multiplexed ADCs connect many analog input channels to a single ADC. The ADC can then scan through the multiple input channels either continuously or in bursts based on an external trigger (many times an ePWM trigger in C2000 applications).

For the sake of charge-sharing, the sample rate on a given channel is important, not the full sample rate of the ADC. This is because charge-sharing equalization will only occur when the particular multiplexed channel is sampled and the source capacitance will have the entire time between sampling to recharge, even if other channels are sampled in the meantime. In applications where the ePWM is triggering the ADC periodically, the sample rate on a given multiplexed channel will match the ePWM triggering frequency.