SLASEL1D June   2017  – August 2018 DAC60508 , DAC70508 , DAC80508

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Block Diagram
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin 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 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 Digital-to-Analog Converter (DAC) Architecture
        1. 8.3.1.1 DAC Transfer Function
        2. 8.3.1.2 Output Amplifiers
        3. 8.3.1.3 DAC Register Structure
          1. 8.3.1.3.1 DAC Register Synchronous and Asynchronous Updates
          2. 8.3.1.3.2 Broadcast DAC Register
          3. 8.3.1.3.3 CLEAR Operation (DACx0508C only)
      2. 8.3.2 Internal Reference
        1. 8.3.2.1 Reference Divider
        2. 8.3.2.2 Solder Heat Reflow
      3. 8.3.3 Device Reset Options
        1. 8.3.3.1 Power-on-Reset (POR)
        2. 8.3.3.2 Software Reset
    4. 8.4 Device Functional Modes
      1. 8.4.1 Stand-Alone Operation
      2. 8.4.2 Daisy-Chain Operation
      3. 8.4.3 Frame Error Checking
      4. 8.4.4 Power-Down Mode
    5. 8.5 Programming
    6. 8.6 Register Map
      1. 8.6.1 NOP Register (address = 0x00) [reset = 0x0000]
        1. Table 9. NOP Register Field Descriptions
      2. 8.6.2 DEVICE ID Register (address = 0x01) [reset = 0x---]
        1. Table 10. DEVICE ID Field Descriptions
      3. 8.6.3 SYNC Register (address = 0x2) [reset = 0xFF00]
        1. Table 11. SYNC Register Field Descriptions
      4. 8.6.4 CONFIG Register (address = 0x3) [reset = 0x0000]
        1. Table 12. CONFIG Register Field Descriptions
      5. 8.6.5 GAIN Register (address = 0x04) [reset = 0x---]
        1. Table 13. GAIN Register Field Descriptions
      6. 8.6.6 TRIGGER Register (address = 0x05) [reset = 0x0000]
        1. Table 14. TRIGGER Register Field Descriptions
      7. 8.6.7 BRDCAST Register (address = 0x6) [reset = 0x0000]
        1. Table 15. BRDCAST Register Field Descriptions
      8. 8.6.8 STATUS Register (address = 0x7) [reset = 0x0000]
        1. Table 16. STATUS Register Field Descriptions
      9. 8.6.9 DACx Register (address = 0x8 to 0xF) [reset = 0x0000 or 0x8000]
        1. Table 17. DACx Register Field Descriptions
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Interfacing to Microcontroller
      2. 9.1.2 Programmable Current Source Circuit
    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 Examples
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.1.2 Programmable Current Source Circuit

The DACx0508 can be integrated into the circuit in Figure 77 to implement an improved Howland current pump for precise voltage to current conversions. Bidirectional current flow and high voltage compliance are two features of the circuit. With a matched resistor network, the load current of the circuit is shown by Equation 2.

Equation 2. DAC80508 DAC70508 DAC60508 EQ2_slasel1.gif

The value of R3 in Equation 2 can be reduced to increase the output current drive of U3. U3 can drive ±20 mV in both directions with voltage compliance limited up to 15 V by the U3 voltage supply. Elimination of the circuit compensation capacitor C1 in the circuit is not suggested as a result of the change in the output impedance ZO, according to Equation 3.

Equation 3. DAC80508 DAC70508 DAC60508 EQ3_slase73.gif

As shown in Equation 3, with matched resistors, ZO is infinite and the circuit is optimum for use as a current source. However, if unmatched resistors are used, ZO is positive or negative with negative output impedance being a potential cause of oscillation. Therefore, by incorporating C1 into the circuit, possible oscillation problems are eliminated. The value of C1 can be determined for critical applications; for most applications, however, a value of several pF is suggested.

DAC80508 DAC70508 DAC60508 Prog_Bid_Cur_So_slasel1.gifFigure 77. Programmable Bidirectional Current Source Circuit