SBAS710A September   2016  – June 2017 ADS9120

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
    6. 6.6  Timing Requirements: Conversion Cycle
    7. 6.7  Timing Requirements: Asynchronous Reset, NAP, and PD
    8. 6.8  Timing Requirements: SPI-Compatible Serial Interface
    9. 6.9  Timing Requirements: Source-Synchronous Serial Interface (External Clock)
    10. 6.10 Timing Requirements: Source-Synchronous Serial Interface (Internal Clock)
    11. 6.11 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 Converter Module
        1. 7.3.1.1 Sample-and-Hold Circuit
        2. 7.3.1.2 External Reference Source
        3. 7.3.1.3 Internal Oscillator
        4. 7.3.1.4 ADC Transfer Function
      2. 7.3.2 Interface Module
    4. 7.4 Device Functional Modes
      1. 7.4.1 RST State
      2. 7.4.2 ACQ State
      3. 7.4.3 CNV State
    5. 7.5 Programming
      1. 7.5.1 Data Transfer Frame
      2. 7.5.2 Interleaving Conversion Cycles and Data Transfer Frames
      3. 7.5.3 Data Transfer Protocols
        1. 7.5.3.1 Protocols for Configuring the Device
        2. 7.5.3.2 Protocols for Reading From the Device
          1. 7.5.3.2.1 Legacy, SPI-Compatible (SYS-xy-S) Protocols
          2. 7.5.3.2.2 SPI-Compatible Protocols with Bus Width Options
          3. 7.5.3.2.3 Source-Synchronous (SRC) Protocols
            1. 7.5.3.2.3.1 Output Clock Source Options with SRC Protocols
            2. 7.5.3.2.3.2 Bus Width Options with SRC Protocols
            3. 7.5.3.2.3.3 Output Data Rate Options with SRC Protocols
      4. 7.5.4 Device Setup
        1. 7.5.4.1 Single Device: All multiSPI™ Options
        2. 7.5.4.2 Single Device: Minimum Pins for a Standard SPI Interface
        3. 7.5.4.3 Multiple Devices: Daisy-Chain Topology
        4. 7.5.4.4 Multiple Devices: Star Topology
    6. 7.6 Register Maps
      1. 7.6.1 Device Configuration and Register Maps
        1. 7.6.1.1 PD_CNTL Register (address = 010h)
        2. 7.6.1.2 SDI_CNTL Register (address = 014h)
        3. 7.6.1.3 SDO_CNTL Register (address = 018h)
        4. 7.6.1.4 DATA_CNTL Register (address = 01Ch)
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 ADC Input Driver
      2. 8.1.2 Input Amplifier Selection
      3. 8.1.3 Charge Kickback Filter
      4. 8.1.4 ADC Reference Driver
    2. 8.2 Typical Application
      1. 8.2.1 Data Acquisition (DAQ) Circuit for Lowest Distortion and Noise Performance With Differential Input
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
      2. 8.2.2 DAQ Circuit With FDA Input Driver and Single-Ended or Differential Input
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curves
  9. 9 Power-Supply Recommendations
    1. 9.1 Power-Supply Decoupling
    2. 9.2 Power Saving
      1. 9.2.1 NAP Mode
      2. 9.2.2 PD Mode
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Signal Path
      2. 10.1.2 Grounding and PCB Stack-Up
      3. 10.1.3 Decoupling of Power Supplies
      4. 10.1.4 Reference Decoupling
      5. 10.1.5 Differential Input Decoupling
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

10 Layout

10.1 Layout Guidelines

This section provides some recommended layout guidelines for achieving optimum performance with the ADS9120 device.

10.1.1 Signal Path

As illustrated in Figure 106, the analog input and reference signals are routed in opposite directions to the digital connections. This arrangement prevents noise generated by digital switching activity from coupling to sensitive analog signals.

10.1.2 Grounding and PCB Stack-Up

Low inductance grounding is critical for achieving optimum performance. Grounding inductance is kept below 1 nH with 15-mil grounding vias and a printed circuit board (PCB) layout design that has at least four layers. Place all critical components of the signal chain on the top layer with a solid analog ground from subsequent inner layers to minimize via length to ground.

Pins 11 and 15 of the ADS9120 can be easily grounded with very low inductance by placing at least four 8-mil grounding vias at the ADS9120 thermal pad. Afterwards, pins 11 and 15 can be connected directly to the grounded thermal path.

10.1.3 Decoupling of Power Supplies

Place the AVDD and DVDD supply decoupling capacitors within 20 mil from the supply pins and use a 15-mil via to ground from each capacitor. Avoid placing vias between any supply pin and its decoupling capacitor.

10.1.4 Reference Decoupling

Dynamic currents are also present at the REFP and REFM pins during the conversion phase and excellent decoupling is required to achieve optimum performance. Three 10-μF, X7R-grade, ceramic capacitors with 10-V rating are recommended, placed as illustrated in Figure 106. Select 0603- or 0805-size capacitors to keep ESL low. The REFM pin of each pair must be connected to the decoupling capacitor before a ground via.

10.1.5 Differential Input Decoupling

Dynamic currents are also present at the differential analog inputs of the ADS9120. C0G- or NPO-type capacitors are required to decouple these inputs because their capacitance stays almost constant over the full input voltage range. Lower quality capacitors (such as X5R and X7R) have large capacitance changes over the full input voltage range that can cause degradation in the performance of the ADS9120.

10.2 Layout Example

ADS9120 apps_layout_sbas629.gif Figure 106. Recommended Layout