SBAS931B January   2019  – July 2022 ADS8353-Q1

PRODUCTION DATA  

  1. 1Features
  2. 2Applications
  3. 3Description
  4. 4Revision History
  5. 5Pin Configuration and Functions
  6. 6Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Thermal Information
    4. 6.4 Recommended Operating Conditions
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Timing Diagram
    9. 6.9 Typical Characteristics
  7. 7Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Reference
      2. 7.3.2 Analog Inputs
        1. 7.3.2.1 Analog Input: Full-Scale Range Selection
        2. 7.3.2.2 Analog Input: Single-Ended and Pseudo-Differential Configurations
      3. 7.3.3 Transfer Function
    4. 7.4 Device Functional Modes
    5. 7.5 Programming
      1. 7.5.1 Serial Interface
      2. 7.5.2 Write to User-Programmable Registers
      3. 7.5.3 Data Read Operation
        1. 7.5.3.1 Reading User-Programmable Registers
        2. 7.5.3.2 Conversion Data Read
          1. 7.5.3.2.1 32-CLK, Dual-SDO Mode (CFR.B11 = 0, CFR.B10 = 0, Default)
          2. 7.5.3.2.2 32-CLK, Single-SDO Mode (CFR.B11 = 0, CFR.B10 = 1)
      4. 7.5.4 Low-Power Modes
        1. 7.5.4.1 STANDBY Mode
        2. 7.5.4.2 Software Power-Down (SPD) Mode
      5. 7.5.5 Frame Abort, Reconversion, or Short-Cycling
    6. 7.6 Register Maps
      1. 7.6.1 ADS8353-Q1 Registers
  8. 8Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Input Amplifier Selection
      2. 8.1.2 Charge Kickback Filter
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curve
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  9. 9Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
      1.      Mechanical, Packaging, and Orderable Information

8.1.1 Input Amplifier Selection

Selection criteria for the input amplifiers is highly dependent on the input signal type and the performance goals of the data acquisition system. Some key amplifier specifications to consider while selecting an appropriate amplifier to drive the inputs of the ADC are:

  • Small-signal bandwidth. Select the small-signal bandwidth of the input amplifiers to be as high as possible after meeting the power budget of the system. Higher bandwidth reduces the closed-loop output impedance of the amplifier, thus allowing the amplifier to more easily drive the low cutoff frequency RC filter at the ADC inputs. Higher bandwidth also minimizes the harmonic distortion at higher input frequencies. Select the amplifier bandwidth as described in Equation 6 to maintain the overall stability of the input driver circuit:
    Equation 6. GUID-5C4E073A-3FE5-4129-B1E0-E14A9BC926A5-low.gif
  • Noise. Noise contribution of the front-end amplifiers must be as low as possible to prevent any degradation in SNR performance of the system. As a rule of thumb, to ensure that the noise performance of the data acquisition system is not limited by the front-end circuit, keep the total noise contribution from the front-end circuit below 20% of the input-referred noise of the ADC. Equation 7 calculates noise from the input driver circuit. This noise is band-limited by designing a low cutoff frequency RC filter:
    Equation 7. GUID-CFEE09B9-6E80-4EF6-BBC0-90A7D0C32DE1-low.gif

    where:

    • V1/f_AMP_PP = the peak-to-peak flicker noise in µV
    • en_RMS = the amplifier broadband noise density in nV/√ Hz
    • f–3dB = the 3-dB bandwidth of the RC filter
    • NG = the noise gain of the front-end circuit, which is equal to 1 in a buffer configuration
  • Distortion. Both the ADC and the input driver introduce nonlinearity in a data acquisition block. As a rule of thumb, the distortion of the input driver must be at least 10 dB lower than the distortion of the ADC, as shown in Equation 8, to ensure that the distortion performance of the data acquisition system is not limited by the front-end circuit.
    Equation 8. GUID-D0C8AF76-2D34-4BBA-92FF-0428FCBC26BC-low.gif
  • Settling Time. For dc signals with fast transients that are common in a multiplexed application, the input signal must settle to the desired accuracy at the inputs of the ADC during the acquisition time window. This condition is critical to maintain the overall linearity performance of the ADC. Typically, the amplifier data sheets specify the output settling performance only up to 0.1% to 0.001%, which may not be sufficient for the desired accuracy. Therefore, always verify the settling behavior of the input driver with TINA™-SPICE simulations before selecting the amplifier.