SBAS728A November   2016  – June 2017 ADS8900B , ADS8902B , ADS8904B

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
    7. 6.7 Switching Characteristics
    8. 6.8 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 LDO Module
      2. 7.3.2 Reference Buffer Module
      3. 7.3.3 Converter Module
        1. 7.3.3.1 Sample-and-Hold Circuit
        2. 7.3.3.2 Internal Oscillator
        3. 7.3.3.3 ADC Transfer Function
      4. 7.3.4 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 Output Data Word
      2. 7.5.2 Data Transfer Frame
      3. 7.5.3 Interleaving Conversion Cycles and Data Transfer Frames
      4. 7.5.4 Data Transfer Protocols
        1. 7.5.4.1 Protocols for Configuring the Device
        2. 7.5.4.2 Protocols for Reading From the Device
          1. 7.5.4.2.1 Legacy, SPI-Compatible (SYS-xy-S) Protocols
          2. 7.5.4.2.2 SPI-Compatible Protocols with Bus Width Options
          3. 7.5.4.2.3 Source-Synchronous (SRC) Protocols
            1. 7.5.4.2.3.1 Output Clock Source Options with SRC Protocols
            2. 7.5.4.2.3.2 Bus Width Options With SRC Protocols
            3. 7.5.4.2.3.3 Output Data Rate Options With SRC Protocols
      5. 7.5.5 Device Setup
        1. 7.5.5.1 Single Device: All multiSPI Options
        2. 7.5.5.2 Single Device: Minimum Pins for a Standard SPI Interface
        3. 7.5.5.3 Multiple Devices: Daisy-Chain Topology
        4. 7.5.5.4 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 = 04h) [reset = 00h]
        2. 7.6.1.2 SDI_CNTL Register (address = 008h) [reset = 00h]
        3. 7.6.1.3 SDO_CNTL Register (address = 0Ch) [reset = 00h]
        4. 7.6.1.4 DATA_CNTL Register (address = 010h) [reset = 00h]
        5. 7.6.1.5 PATN_LSB Register (address = 014h) [reset = 00h]
        6. 7.6.1.6 PATN_MID Register (address = 015h) [reset = 00h]
        7. 7.6.1.7 PATN_MSB Register (address = 016h) [reset = 00h]
        8. 7.6.1.8 OFST_CAL Register (address = 020h) [reset = 00h]
        9. 7.6.1.9 REF_MRG Register (address = 030h) [reset = 00h]
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 ADC Reference Driver
      2. 8.1.2 ADC Input Driver
        1. 8.1.2.1 Charge-Kickback Filter
        2. 8.1.2.2 Input Amplifier Selection
    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
      3. 8.2.3 Design Requirements
      4. 8.2.4 Detailed Design Procedure
      5. 8.2.5 Application Curves
  9. 9 Power-Supply Recommendations
  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 Related Links
    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

10 Layout

10.1 Layout Guidelines

This section provides some layout guidelines for achieving optimum performance with the ADS890xB device family.

10.1.1 Signal Path

As illustrated in Figure 121, the analog input signals are routed in opposite directions to the digital connections. The reference decoupling components are kept away from the switching digital signals. 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.

For lowest inductance grounding, connect the GND pins of the ADS890xB (pin 11 and pin 15) directly to the device thermal pad and place at least four 8-mil grounding vias on the device thermal pad.

10.1.3 Decoupling of Power Supplies

Place the decoupling capacitors on RVDD, the LDO output, and DVDD within 20 mil from the respective pins, and use a 15-mil via to ground from each capacitor. Avoid placing vias between any supply pin and the respective decoupling capacitor.

10.1.4 Reference Decoupling

Dynamic currents are also present at the REFBUFOUT and REFM pins during the conversion phase, and excellent decoupling is required to achieve optimum performance. Place a 22-μF, X7R-grade, ceramic capacitor with at least 10-V rating and an ESR of 1-Ω between the REFBUFOUT and the REFM pins, as illustrated in Figure 121. Select 0603- or 0805-size capacitors to keep equivalent series inductance (ESL) low. Connect the REFM pins 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 ADS890xB. Use C0G- or NPO-type capacitors to decouple these inputs because with these type of capacitors, 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 may cause degradation in the performance of the device.

10.2 Layout Example

ADS8900B ADS8902B ADS8904B ADS89xxB_Layout_sbas707.gif Figure 121. Recommended Layout