SBAS872B December   2020  – October 2022 ADC3681 , ADC3682 , ADC3683

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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 - Power Consumption
    6. 6.6  Electrical Characteristics - DC Specifications
    7. 6.7  Electrical Characteristics - AC Specifications
    8. 6.8  Timing Requirements
    9. 6.9  Typical Characteristics - ADC3681
    10. 6.10 Typical Characteristics - ADC3682
    11. 6.11 Typical Characteristics - ADC3683
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Analog Input
        1. 8.3.1.1 Analog Input Bandwidth
        2. 8.3.1.2 Analog Front End Design
          1. 8.3.1.2.1 Sampling Glitch Filter Design
          2. 8.3.1.2.2 Analog Input Termination and DC Bias
            1. 8.3.1.2.2.1 AC-Coupling
            2. 8.3.1.2.2.2 DC-Coupling
        3. 8.3.1.3 Auto-Zero Feature
      2. 8.3.2 Clock Input
        1. 8.3.2.1 Single Ended vs Differential Clock Input
        2. 8.3.2.2 Signal Acquisition Time Adjust
      3. 8.3.3 Voltage Reference
        1. 8.3.3.1 Internal voltage reference
        2. 8.3.3.2 External voltage reference (VREF)
        3. 8.3.3.3 External voltage reference with internal buffer (REFBUF)
      4. 8.3.4 Digital Down Converter
        1. 8.3.4.1 DDC MUX
        2. 8.3.4.2 Digital Filter Operation
        3. 8.3.4.3 FS/4 Mixing with Real Output
        4. 8.3.4.4 Numerically Controlled Oscillator (NCO) and Digital Mixer
        5. 8.3.4.5 Decimation Filter
        6. 8.3.4.6 SYNC
        7. 8.3.4.7 Output Formatting with Decimation
      5. 8.3.5 Digital Interface
        1. 8.3.5.1 Output Formatter
        2. 8.3.5.2 Output Scrambler
        3. 8.3.5.3 Output Bit Mapper
        4. 8.3.5.4 Output Interface/Mode Configuration
          1. 8.3.5.4.1 Configuration Example
        5. 8.3.5.5 Output Data Format
      6. 8.3.6 Test Pattern
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation
      2. 8.4.2 Power Down Options
      3. 8.4.3 Digital Channel Averaging
    5. 8.5 Programming
      1. 8.5.1 Configuration using PINs only
      2. 8.5.2 Configuration using the SPI interface
        1. 8.5.2.1 Register Write
        2. 8.5.2.2 Register Read
    6. 8.6 Register Map
      1. 8.6.1 Detailed Register Description
  9. 9 Application Information Disclaimer
    1. 9.1 Typical Application
      1. 9.1.1 Design Requirements
      2. 9.1.2 Detailed Design Procedure
        1. 9.1.2.1 Input Signal Path
        2. 9.1.2.2 Sampling Clock
        3. 9.1.2.3 Voltage Reference
      3. 9.1.3 Application Curves
    2. 9.2 Initialization Set Up
      1. 9.2.1 Register Initialization During Operation
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.5.1 Output Formatter

The digital output interface uses a flexible output bit mapper (Figure 8-40). The bit mapper takes the 18-bit output directly from the ADC or from the digital decimation filter block and reformats it to a resolution of 14,16,18 or 20-bit. The output serialization factor is adjusted accordingly for 2-, 1- and 1/2-wire interface modes. The maximum SLVDS interface output data rate can not be exceeded independent of output resolution or serialization factor.

For 14 and 16-bit output resolution, the LSBs are truncated during the reformatting. With 20-bit output, in bypass mode two 0s are added in place of the two LSBs while in decimation mode and the digital averaging mode the full 20-bit output is used.

Figure 8-40 Interface output bit mapper

Table 8-6 provides an overview for the resulting serialization factor depending on output resolution and output modes. Note that the DCLKIN frequency needs to be adjusted accordingly as well. Changing the output resolution to 16-bit, 2-wire mode for example results in DCLKIN = FS * 4 instead of * 4.5.

Table 8-6 Serialization factor vs output resolution for different output modes
OUTPUT RESOLUTIONInterfaceSERIALIZATIONFCLKDCLKINDCLKD0/D1
14-bit2-Wire7xFS/2FS* 3.5FS* 3.5FS* 7
1-Wire14xFSFS* 7FS* 7FS* 14
1/2-Wire28xFSFS* 14FS* 14FS* 28
16-bit2-Wire8xFS/2FS* 4FS* 4FS* 8
1-Wire16xFSFS* 8FS* 8FS* 16
1/2-Wire32xFSFS* 16FS* 16FS* 32
18-bit (default)2-Wire9xFS/2FS* 4.5FS* 4.5FS* 9
1-Wire18xFSFS* 9FS* 9FS* 18
1/2-Wire36xFSFS* 18FS* 18FS* 36
20-bit2-Wire10xFS/2FS* 5FS* 5FS* 10
1-Wire20xFSFS* 10FS* 10FS* 20
1/2-Wire40xFSFS* 20FS* 20FS* 40

The programming sequence to change the output interface and/or resolution from default settings is shown in Section 8.3.5.4.