SPRACZ0A August   2021  – March 2023 F29H850TU , F29H850TU , F29H859TU-Q1 , F29H859TU-Q1 , 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 , TMS320F28P659DH-Q1 , TMS320F28P659DH-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659DK-Q1 , TMS320F28P659SH-Q1 , TMS320F28P659SH-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
      7. 1.1.7 Related Application Reports
      8. 1.1.8 Comparison of Schematic Capture and Simulation Tools
      9. 1.1.9 PSpice for 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 Bias Point Analysis to Determine Voa_ss
    4. 4.4 Transient Analysis to Determine Voa_ss
    5. 4.5 Measure the Settling Error
    6. 4.6 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

4.6 Sweeping Source Resistance

It may sometimes be helpful to run simulations for a range of Rs values. To accomplish this, create a transient simulation profile as shown in Figure 4-15. Then enable the Parametric Sweep option. In the Parametric Sweep settings, choose the global parameter R_STEP as the sweep variable. Then choose a linear sweep type with a start value of 250 Ω, an end value of 750 Ω, and an increment of 250 Ω as shown in Figure 4-16.

GUID-818C3B5E-58B9-4BD1-B06D-443636BB627D-low.jpg Figure 4-15 Transient Analysis Simulation Profile General Settings
GUID-F174055F-7816-40B2-88C8-CE50EA3E5FD0-low.jpg Figure 4-16 Transient Analysis Simulation Profile Parametric Sweep

Once the Parametric Sweep option is configured, a transient analysis can be run as usual. The simulation will now produce an output waveform for each resistance value in the sweep. After simulation, delete all outputs other than Vpin and set Vpin range to +2.995 V to +3 V. Alternatively, go to Window ➔ Display Control... using the menu in the upper left of the PSpice for TI simulation window to access a list of preset display configurations provided by TI. Restore the Sweep Results display configuration. Note that these preset display configurations are only available in the PSpice for TI projects bundled with this application report. Figure 4-17 shows the results of simulating 100kHz sampling with 250 Ω, 500 Ω, and 750 Ω source resistance values. It is recommended to view the results of all output curves simultaneously by placing a probe cursor as shown in Figure 4-17.

GUID-D247E2E2-AA30-4B0D-9572-07627F1B944C-low.jpg Figure 4-17 Source Impedance Sweep Results