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

8.3.2 Voltage Output Stage

The voltage output stage as conceptualized in Figure 8-2 provides the voltage output according to the DAC code and the output range setting. The output range can be programmed as 0 V to 5 V or 0 V to 10 V for unipolar output mode, and ±5 V or ±10 V for bipolar output mode. In addition, an option is available to increase the output voltage range by 10%. The output current drive can be up to 10 mA. The output stage has short-circuit current protection that limits the output current to 30 mA. To maintain proper performance, a minimum 0.5-V power-supply headroom is required. The voltage output is able to drive a capacitive load up to 1 µF. For loads greater than 20 nF, to keep the output voltage stable at the expense of reduced bandwidth and increased settling time, connect an external compensation capacitor between CMP and VOUT. If an external compensation capacitor greater than 470 pF is used, connect an additional 100-pF capacitor from CMP to GND.

GUID-15DE952D-7362-4D2B-9B8C-C41B72C7B502-low.gifFigure 8-2 Voltage Output

The +VSENSE pin is provided to enable sensing of the load by connecting to points electrically closer to the load. This configuration allows the internal output amplifier to make sure that the correct voltage is applied across the load, as long as headroom is available on the power supply. Ideally, this pin is used to correct for resistive drops on the system board and is connected to VOUT at the pins. In some cases, both VOUT and +VSENSE are brought out as pins and, through separate lines, connected remotely together at the load. In case the +VSENSE line is cut, use an optional 5-kΩ resistor between VOUT and +VSENSE to prevent the amplifier loop from breaking. The –VSENSE pin, on the other hand, is provided as a GND sense reference output from the internal VOUT amplifier. The output swing of the VOUT amplifier is relative to the voltage seen at this pin. The actual voltage difference between the –VSENSE pin and the device GND pins is not expected to be more than a few 100 µV. The internal resistor in Figure 8-2 between the device internal GND and the –VSENSE pin is typically 2 kΩ.

After power on, the power-on-reset circuit makes sure that all registers are at their default values. Therefore, the voltage output buffer is in a Hi-Z state; however, the +VSENSE pin connects to the amplifier inputs through an internal 60-kΩ feedback resistor (RFB in Figure 8-2). If the VOUT and +VSENSE pins are connected together, the VOUT pin is also connected to the same node through the feedback resistor. This node is protected by internal circuitry and settles to a value between GND and the reference input.

The output voltage (VOUT) can be expressed as Equation 1 and Equation 2.

For unipolar output mode:

Equation 1. GUID-BF067778-BE04-42A1-823E-13A0CFADE4A6-low.gif

For bipolar output mode:

Equation 2. GUID-9C59525A-5864-44DE-AE9E-D948364C9431-low.gif

where

  • CODE is the decimal equivalent of the code loaded to the DAC
  • N is the bits of resolution; 16 for DAC8760 and 12 for DAC7760
  • VREF is the reference voltage; for internal reference, VREF = 5 V
  • GAIN is automatically selected for a desired voltage output range as shown in Table 8-1
Table 8-1 Voltage Output Range vs Gain Setting(1)
VOLTAGE OUTPUTGAIN
0 V to 5 V1
0 V to 10 V2
±5 V2
±10 V4
(1) VREF = 5 V

The voltage range is set according to the value of the RANGE bits and the OVR bit in the Control Register. The OVR bit makes the gain value in Table 8-1 increase by 10%, thereby increasing the voltage output range, as shown in Table 8-8 (see Section 8.4.1 for more details).