SBAS528D June   2013  – December 2021 DAC7760 , DAC8760

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  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  Electrical Characteristics: AC
    7. 7.7  Timing Requirements: Write Mode
    8. 7.8  Timing Requirements: Readback Mode
    9. 7.9  Timing Diagrams
    10. 7.10 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  Voltage Output Stage
      3. 8.3.3  Current Output Stage
      4. 8.3.4  Internal Reference
      5. 8.3.5  Digital Power Supply
      6. 8.3.6  DAC Clear
      7. 8.3.7  Power-On Reset
      8. 8.3.8  Alarm Detection
      9. 8.3.9  Watchdog Timer
      10. 8.3.10 Frame Error Checking
      11. 8.3.11 User Calibration
      12. 8.3.12 Programmable Slew Rate
    4. 8.4 Device Functional Modes
      1. 8.4.1 Setting Voltage and Current Output Ranges
      2. 8.4.2 Boost Configuration for IOUT
      3. 8.4.3 Filtering the Current Output (only on the VQFN package)
      4. 8.4.4 HART Interface
        1. 8.4.4.1 For 4-mA to 20-mA Mode
        2. 8.4.4.2 For All Current Output Modes
    5. 8.5 Programming
      1. 8.5.1 Serial Peripheral Interface (SPI)
        1. 8.5.1.1 SPI Shift Register
        2. 8.5.1.2 Write Operation
        3. 8.5.1.3 Read Operation
        4. 8.5.1.4 Stand-Alone Operation
        5. 8.5.1.5 Multiple Devices on the Bus
    6. 8.6 Register Maps
      1. 8.6.1 DACx760 Command and Register Map
        1. 8.6.1.1 DACx760 Register Descriptions
          1. 8.6.1.1.1 Control Register
          2. 8.6.1.1.2 Configuration Register
          3. 8.6.1.1.3 DAC Registers
          4. 8.6.1.1.4 Reset Register
          5. 8.6.1.1.5 Status Register
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Controlling the VOUT and IOUT Pins
        1. 9.1.1.1 VOUT and IOUT Pins are Independent Outputs, Never Simultaneously Enabled
        2. 9.1.1.2 VOUT and IOUT Pins are Independent Outputs, Simultaneously Enabled
        3. 9.1.1.3 VOUT and IOUT Pins are Tied Together, Never Simultaneously Enabled
      2. 9.1.2 Implementing HART in All Current Output Modes
        1. 9.1.2.1 Using CAP2 Pin on VQFN Package
        2. 9.1.2.2 Using the ISET-R Pin
      3. 9.1.3 Short-Circuit Current Limiting
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Thermal Considerations
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.12 Programmable Slew Rate

The slew rate control feature controls the rate at which the output voltage or current changes. With the slew rate control feature disabled, the output changes smoothly at a rate limited by the output drive circuitry and the attached load.

To reduce the slew rate, enable the slew rate control feature through bit 4 of Table 8-17. With this feature enabled, the output does not slew directly between the two values. Instead, the output steps digitally at a rate defined by bits [7:5] (SRSTEP) and bits [11:8] (SRCLK) of the control register. SRCLK defines the rate at which the digital slew updates; SRSTEP defines the amount by which the output value changes at each update. If the DAC data register is read while the DAC output is still changing, the instantaneous value is read. Table 8-5 lists the slew rate step-size options. Table 8-6 summarizes the slew rate update clock options.

Table 8-5 Slew Rate Step-Size (SRSTEP) Options
SRSTEPSTEP SIZE (LSB)
DAC7760DAC8760
0000.06251
0010.1252
0100.254
0110.58
100116
101232
110464
1118128
Table 8-6 Slew Rate Update Clock (SRCLK) Options
SRCLKDAC UPDATE FREQUENCY (Hz)
0000258,065
0001200,000
0010153,845
0011131,145
0100115,940
010169,565
011037,560
011125,805
100020,150
100116,030
101010,295
10118,280
11006,900
11015,530
11104,240
11113,300

The time required for the output to slew over a given range can be expressed as Equation 7:

Equation 7. GUID-D7CD9E6A-E16D-43D3-8941-EF25AB216FF9-low.gif

where

  • Slew Time is expressed in seconds
  • Output Change is expressed in amps (A) for IOUT or volts (V) for VOUT

When the slew rate control feature is enabled, all output changes happen at the programmed slew rate. This configuration results in a staircase formation at the output. If the CLR pin is asserted, the output slews to the zero-scale value at the programmed slew rate. To verify that the slew operation has completed, read Bit 1 (SR-ON) of the Status Register. The update clock frequency for any given value is the same for all output ranges. The step size, however, varies across output ranges for a given value of step size because the LSB size is different for each output range. Figure 8-5 illustrates an example of IOUT slewing at a rate set by the previously described parameters. In this example for the DAC8760 (LSB size of 305 nA for the 0-mA to 20-mA range), the settings correspond to an update clock frequency of 6.9 kHz and a step size of 128 LSB. As shown for the case with no capacitors on CAP1 or CAP2, the steps occur at the update clock frequency (6.9 kHz corresponds to a period close to 150 µs) and the size of each step is about 38 µA (128 × 305 nA). The slew time for a specific code change can be calculated using Equation 7.

GUID-8A15ADA2-989D-4767-934A-E27CB29D45FB-low.pngFigure 8-5 IOUT vs Time With Digital Slew Rate Control

Apply the desired programmable slew rate control setting prior to updating the DAC data register because updates to the DAC data register in tandem with updates to the slew rate control registers can create race conditions that may result in unexpected DAC data.