SBAS761A February   2020  – February 2020 ADS8355

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Block Diagram
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1      Absolute Maximum Ratings
    2. 6.2      ESD Ratings
    3. 6.3      Recommended Operating Conditions
    4. 6.4      Thermal Information
    5. 6.5      Electrical Characteristics
    6. Table 1. Timing Requirements
    7. Table 2. Switching Characteristics
    8. 6.6      Typical Characteristics
  7. 7 Detailed 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
      1. 7.4.1 Conversion Data Read: Dual-SDO Mode (Default)
      2. 7.4.2 Conversion Data Read: Single-SDO Mode
      3. 7.4.3 Low-Power Modes
        1. 7.4.3.1 STANDBY Mode
        2. 7.4.3.2 PD (Power-Down) Mode
    5. 7.5 Programming
      1. 7.5.1 Register Read/Write Operation
    6. 7.6 Register Map
      1. 7.6.1 ADS8355 Registers
        1. 7.6.1.1  PD_STANDBY Register (Offset = 4h) [reset = 0h]
          1. Table 9. PD_STANDBY Register Field Descriptions
        2. 7.6.1.2  PD_KEY Register (Offset = 5h) [reset = 0h]
          1. Table 10. PD_KEY Register Field Descriptions
        3. 7.6.1.3  SDO_CTRL Register (Offset = Dh) [reset = 0h]
          1. Table 11. SDO_CTRL Register Field Descriptions
        4. 7.6.1.4  DATA_OUT_CTRL Register (Offset = 11h) [reset = 0h]
          1. Table 12. DATA_OUT_CTRL Register Field Descriptions
        5. 7.6.1.5  REF_SEL Register (Offset = 20h) [reset = 0h]
          1. Table 13. REF_SEL Register Field Descriptions
        6. 7.6.1.6  REFDAC_A_LSB Register (Offset = 24h) [reset = 0h]
          1. Table 14. REFDAC_A_LSB Register Field Descriptions
        7. 7.6.1.7  REFDAC_A_MSB Register (Offset = 25h) [reset = 0h]
          1. Table 15. REFDAC_A_MSB Register Field Descriptions
        8. 7.6.1.8  REFDAC_B_LSB Register (Offset = 26h) [reset = 0h]
          1. Table 16. REFDAC_B_LSB Register Field Descriptions
        9. 7.6.1.9  REFDAC_B_MSB Register (Offset = 27h) [reset = 0h]
          1. Table 17. REFDAC_B_MSB Register Field Descriptions
        10. 7.6.1.10 INPUT_CONFIG Register (Offset = 28h) [reset = 0h]
          1. Table 18. INPUT_CONFIG Register Field Descriptions
  8. 8 Application 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
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2 Detailed Design Procedure

Best practice is for the distortion from the input driver to be at least 10 dB less than the ADC distortion. The distortion resulting from variation in the common-mode signal is eliminated by using the amplifier in an inverting gain configuration that establishes a fixed common-mode level for the circuit. This configuration also eliminates the requirement of rail-to-rail swing at the amplifier input. The low-power OPA320, used as an input driver, provides exceptional AC performance because of its extremely low-distortion and high-bandwidth specifications. In addition, the components of the antialiasing filter are such that the noise from the front-end circuit is kept low without adding distortion to the input signal.

The application circuit illustrated in Figure 44 is optimized to achieve the lowest distortion and lowest noise for a
10-kHz input signal fed to the ADS8355 operating at full throughput with the default dual-SDO interface mode. The input signal is processed through a high-bandwidth, low-distortion amplifier in an inverting gain configuration and a low-pass RC filter before being fed into the device.

Figure 45 illustrates the reference driver circuit when operation with an external reference is desired. The reference voltage is generated by the high-precision, low-noise REF3425 circuit. The output broadband noise of the reference is heavily filtered by a low-pass filter with a 3-dB cutoff frequency of 160 Hz. The decoupling capacitor on each reference pin is selected to be 10 µF. The low output impedance, low noise, and fast settling time make the OPA2320 a good choice for driving this high capacitive load.