SLAS605C June   2008  – July 2018 ADS7950 , ADS7951 , ADS7952 , ADS7953 , ADS7954 , ADS7955 , ADS7956 , ADS7957 , ADS7958 , ADS7959 , ADS7960 , ADS7961

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     Detailed Block Diagram
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions: TSSOP Packages
    2.     Pin Functions: VQFN Packages
  7. 7 Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information: TSSOP
    5. 7.5  Thermal Information: VQFN
    6. 7.6  Electrical Characteristics: ADS7950, ADS7951, ADS7952, ADS7953
    7. 7.7  Electrical Characteristics, ADS7954, ADS7955, ADS7956, ADS7957
    8. 7.8  Electrical Characteristics, ADS7958, ADS7959, ADS7960, ADS7961
    9. 7.9  Timing Requirements
    10. 7.10 Typical Characteristics (All ADS79xx Family Devices)
    11. 7.11 Typical Characteristics (12-Bit Devices Only)
    12. 7.12 Typical Characteristics (12-Bit Devices Only)
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Reference
      2. 8.3.2 Power Saving
    4. 8.4 Device Functional Modes
      1. 8.4.1 Channel Sequencing Modes
      2. 8.4.2 Device Programming and Mode Control
        1. 8.4.2.1 Mode Control Register
        2. 8.4.2.2 Program Registers
      3. 8.4.3 Device Power-Up Sequence
      4. 8.4.4 Operating in Manual Mode
      5. 8.4.5 Operating in Auto-1 Mode
      6. 8.4.6 Operating in Auto-2 Mode
      7. 8.4.7 Continued Operation in a Selected Mode
    5. 8.5 Programming
      1. 8.5.1 Digital Output
      2. 8.5.2 GPIO Registers
      3. 8.5.3 Alarm Thresholds for GPIO Pins
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Analog Input
    2. 9.2 Typical Applications
      1. 9.2.1 Unbuffered Multiplexer Output (MXO)
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
        3. 9.2.1.3 Application Curves
      2. 9.2.2 OPA192 Buffered Multiplexer Output (MXO)
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Examples
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Related Links
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • RHB|32
  • DBT|38
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2.2 Detailed Design Procedure

The design procedure is similar to the unbuffered-MXO application, but includes an operation amplifier in unity gain as a buffer. The most important parameter for multiplexer buffering is slew rate. The amplifier must finish slewing before the start of sampling (acquisition) to keep the buffer operating in small-signal mode during sampling (acquisition) time. Also, between the buffer output and converter input (INP), there must be a capacitor large enough to keep the buffer in small-signal operation during sampling (acquisition) time. Because 150 pF is large enough to protect the buffer form hold charge from internal capacitors, this value selected along with the lowest impedance that allows the op amp to remain stable.

The converter allows the MXO to settle approximately 600 ns before sampling. During this time, the buffer slews and then enters small-signal operation. For a 5-V step change, slew rate stays constant during the first 4 V. The last 1 V includes a transition from slewing and non-slewing. Thus, the buffer cannot be assumed to keep a constant slew during the 600 ns available for MXO settling. Assuming that the last 1-V slew is reduced to half is recommended. For this reason, slew is 10 V/µs or (5 Vref + 1 V) / 0.6 µs to account for the 1-V slow slew. The OPA192 has a 20-V/us slew, and is capable of driving 150 pF with more than a 50° phase margin with a 50-Ω or 100-Ω Riso, making the OPA192 an ideal selection for the ADS79xx-Q1 family of converters.