SNAS449F February   2008  – May 2017 DAC081C081 , DAC081C085

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1. 3.1 Block Diagram
  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 Section
      2. 8.3.2 Output Amplifier
      3. 8.3.3 Reference Voltage
      4. 8.3.4 Power-On Reset
      5. 8.3.5 Simultaneous Reset
      6. 8.3.6 Additional Timing Information: toutz
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power-Down Modes
    5. 8.5 Programming
      1. 8.5.1 Serial Interface
      2. 8.5.2 Basic I2C Protocol
      3. 8.5.3 Standard-Fast Mode
      4. 8.5.4 High-Speed (Hs) Mode
      5. 8.5.5 I2C Slave (Hardware) Address
      6. 8.5.6 Writing to the DAC Register
      7. 8.5.7 Reading from the DAC Register
    6. 8.6 Registers
      1. 8.6.1 DAC Register
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Bipolar Operation
      2. 9.1.2 DSP/Microprocessor Interfacing
        1. 9.1.2.1 Interfacing to the 2-Wire Bus
        2. 9.1.2.2 Interfacing to a Hs-mode Bus
    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
    1. 10.1 Using References as Power Supplies
      1. 10.1.1 LM4132
      2. 10.1.2 LM4050
      3. 10.1.3 LP3985
      4. 10.1.4 LP2980
  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 Development Support
      2. 12.1.2 Device Nomenclature
        1. 12.1.2.1 Specification Definitions
    2. 12.2 Related Links
    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

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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 Bipolar Operation

The DAC081C081 is designed for single-supply operation and thus has a unipolar output. However, a bipolar output may be obtained with the circuit in Figure 27. This circuit will provide an output voltage range of ±5 Volts. A rail-to-rail amplifier should be used if the amplifier supplies are limited to ±5 V.

DAC081C081 DAC081C085 30052317.gif Figure 27. Bipolar Operation

The output voltage of this circuit for any code is found to be

Equation 2. VO = (VA × (D / 256) × ((R1 + R2) / R1) – VA × R2 / R1)

where

  • D is the input code in decimal form.

With VA = 5V and R1 = R2,

Equation 3. VO = (10 × D / 256) – 5 V

A list of rail-to-rail amplifiers suitable for this application are indicated in Table 4.

Table 4. Some Rail-to-Rail Amplifiers

AMP PKGS  TYP VOS TYP ISUPPLY
LMP7701 SOT23-5 37 uV 0.79 mA
LMV841 SC70-5 50 uV 1 mA
LMC7111 SOT23-5 0.9 mV 25 µA
LM7301 SO-8
SOT23-5		 0.03 mV 620 µA
LM8261 SOT23-5 0.7 mV 1 mA

9.1.2 DSP/Microprocessor Interfacing

Interfacing the DAC081C081 to microprocessors and DSPs is quite simple. The following guidelines are offered to simplify the design process.

9.1.2.1 Interfacing to the 2-Wire Bus

Figure 28 shows a microcontroller interfacing to the DAC081C081 through the 2-wire bus. Pullup resistors (Rp) should be chosen to create an appropriate bus rise time and to limit the current that will be sunk by the open-drain outputs of the devices on the bus. Please refer to the I2C Specification for further details. Typical pullup values to use in standard-fast mode bus applications are 2 kΩ to 10 kΩ. SCL and SDA series resisters (RS) near the DAC081C081 are optional. If high-voltage spikes are expected on the 2-wire bus, series resistors should be used to filter the voltage on SDA and SCL. The value of the series resistance must be picked to ensure the VIL threshold can be achieved. If used, RS is typically 51 Ω.

DAC081C081 DAC081C085 30052309.gif Figure 28. Serial Interface Connection Diagram

9.1.2.2 Interfacing to a Hs-mode Bus

Interfacing to a Hs-mode bus is very similar to interfacing to a standard-fast mode bus. In Hs-mode, the specified rise time of SCL is shortened. To create a faster rise time, the master device (microcontroller) can drive the SCL bus high and low. In other words, the microcontroller can drive the line high rather than leaving it to the pullup resistor. It is also possible to decrease the value of the pullup resistors or increase the pullup current to meet the tighter timing specs. Please refer to the I2C Specification for further details.

9.2 Typical Application

DAC081C081 DAC081C085 typ_app_SNAS449.gif Figure 29. Pressure Sensor Gain Adjust

9.2.1 Design Requirements

A positive supply only data acquisition system capable of digitizing a pressure sensor output. In addition to digitizing the pressure sensor output, the system designer can use the DAC081C081 to correct for gain errors in the pressure sensor output by adjusting the bias voltage to the bridge pressure sensor.

9.2.2 Detailed Design Procedure

As shown in Equation 4, the output of the pressure sensor is relative to the imbalance of the resistive bridge times the output of the DAC081C081, thus providing the desired gain correction.

Equation 4. Pressure Sensor Output = (DAC_Output × [(R2 / (R1 + R2) – (R4 / (R3 + R4)]

Likewise for the ADC161S626, Equation 5 shows that the ADC output is function of the pressure sensor output times relative to the ratio of the ADC input divided by the DAC081C081 output voltage.

Equation 5. ADC161S626 Output = (Pressure Sensor Output × 100 /(2 × VREF) ) × 216

9.2.3 Application Curve

DAC081C081 DAC081C085 30052320.png Figure 30. INL vs Input Code