SNAS407H August   2007  – April 2015 DAC128S085

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
  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
    5. 7.5 Electrical Characteristics
    6. 7.6 AC and Timing Characteristics
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 DAC Architecture
      2. 8.3.2 Output Amplifiers
      3. 8.3.3 Reference Voltage
      4. 8.3.4 Serial Interface
      5. 8.3.5 Daisy-Chain Operation
      6. 8.3.6 DAC Input Data Update Mechanism
      7. 8.3.7 Power-On Reset
      8. 8.3.8 Transfer Characteristic
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power-Down Modes
    5. 8.5 Programming
      1. 8.5.1 Programming the DAC128S085
        1. 8.5.1.1 Updating DAC Outputs Simultaneously
        2. 8.5.1.2 Updating DAC Outputs Independently
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Using References as Power Supplies
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Specification Definitions
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

9.1.1 Using References as Power Supplies

While the simplicity of the DAC128S085 implies ease of use, it is important to recognize that the path from the reference input (VREF1,2) to the DAC outputs has a zero Power Supply Rejection Ratio (PSRR). Therefore, the user must provide a noise-free supply voltage to VREF1,2. To utilize the full dynamic range of the DAC128S085, the supply pin (VA) and VREF1,2 can be connected together and share the same supply voltage. Because the DAC128S085 consumes very little power, a reference source can be used as the reference input or the supply voltage. The advantages of using a reference source over a voltage regulator are accuracy and stability. Some low-noise regulators can also be used. Listed below are a few reference and power supply options for the DAC128S085.

9.2 Typical Application

The LM4132, with its ±0.05% accuracy over temperature, is a good choice as a reference source for the DAC128S085. The 4.096-V version is useful for a 0-V to 4.095-V output range. Bypassing the LM4132 voltage input pin with a 4.7-µF capacitor and the voltage output pin with a 4.7-µF capacitor improves stability and reduces output noise. The LM4132 comes in a space-saving 5-pin SOT-23.

DAC128S085 Typical_Application_Circuit_SNAS407.gifFigure 32. The LM4132 as a Power Supply

9.2.1 Design Requirements

There are two references for the DAC128S085. One reference input serves channels A through D, while the other reference serves channels E through H. The 16-bit input shift register of the DAC128S085 controls the mode of operation, the power-down condition, and the register/output value of the DAC channels. All eight DAC outputs can be updated simultaneously or individually.

9.2.2 Detailed Design Procedure

Each reference input pin can be set independently, or the reference pins can be shorted together as shown in Figure 32. Acceptable reference voltages are 0.5 V to VA. Utilizing an RC filter on the output to roll off output noise is optional.

9.2.3 Application Curve

DAC128S085 30016924.pngFigure 33. Typical Performance