SBAS608C June   2014  – December 2015 ADS7042

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Companion Products
  6. 6 Device Comparison
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Characteristics
    7. 8.7 Typical Characteristics
  9. 9 Parameter Measurement Information
    1. 9.1 Digital Voltage Levels
  10. 10Detailed Description
    1. 10.1 Overview
    2. 10.2 Functional Block Diagram
    3. 10.3 Feature Description
      1. 10.3.1 Reference
      2. 10.3.2 Analog Input
      3. 10.3.3 ADC Transfer Function
      4. 10.3.4 Serial Interface
    4. 10.4 Device Functional Modes
      1. 10.4.1 Offset Calibration
        1. 10.4.1.1 Offset Calibration on Power-Up
        2. 10.4.1.2 Offset Calibration During Normal Operation
  11. 11Application and Implementation
    1. 11.1 Application Information
    2. 11.2 Typical Applications
      1. 11.2.1 Single-Supply DAQ with the ADS7042
        1. 11.2.1.1 Design Requirements
        2. 11.2.1.2 Detailed Design Procedure
          1. 11.2.1.2.1 Antialiasing Filter
          2. 11.2.1.2.2 Input Amplifier Selection
          3. 11.2.1.2.3 Reference Circuit
        3. 11.2.1.3 Application Curve
      2. 11.2.2 DAQ Circuit with the ADS7042 for Maximum SINAD
        1. 11.2.2.1 Design Requirements
        2. 11.2.2.2 Detailed Design Procedure
        3. 11.2.2.3 Application Curves
      3. 11.2.3 12-Bit, 10-kSPS DAQ Circuit Optimized for DC Sensor Measurements
        1. 11.2.3.1 Design Requirements
        2. 11.2.3.2 Detailed Design Procedure
        3. 11.2.3.3 Application Curve
  12. 12Power-Supply Recommendations
    1. 12.1 AVDD and DVDD Supply Recommendations
    2. 12.2 Estimating Digital Power Consumption
    3. 12.3 Optimizing Power Consumed by the Device
  13. 13Layout
    1. 13.1 Layout Guidelines
    2. 13.2 Layout Example
  14. 14Device and Documentation Support
    1. 14.1 Documentation Support
      1. 14.1.1 Related Documentation
    2. 14.2 Community Resources
    3. 14.3 Trademarks
    4. 14.4 Electrostatic Discharge Caution
    5. 14.5 Glossary
  15. 15Mechanical, Packaging, and Orderable Information

12 Power-Supply Recommendations

12.1 AVDD and DVDD Supply Recommendations

The ADS7042 has two separate power supplies: AVDD and DVDD. The device operates on AVDD; DVDD is used for the interface circuits. AVDD and DVDD can be independently set to any value within the permissible ranges. The AVDD supply also defines the full-scale input range of the device. Always set the AVDD supply to be greater than or equal to the maximum input signal to avoid saturation of codes. Decouple the AVDD and DVDD pins individually with 1-µF ceramic decoupling capacitors, as shown in Figure 46. The minimum capacitor value required for AVDD and DVDD is 200 nF and 20 nF, respectively. If both supplies are powered from the same source, a minimum capacitor value of 220 nF is required for decoupling.

ADS7042 ai_supply_bas608.gif Figure 46. Power-Supply Decoupling

12.2 Estimating Digital Power Consumption

The current consumption from the DVDD supply depends on the DVDD voltage, load capacitance on the SDO line, and the output code. The load capacitance on the SDO line is charged by the current from the SDO pin on every rising edge of the data output and is discharged on every falling edge of the data output. The current consumed by the device from the DVDD supply can be calculated by Equation 5:

Equation 5. IDVDD = C × V × f

where

  • C = Load capacitance on the SDO line,
  • V = DVDD supply voltage, and
  • f = Number of transitions on the SDO output.

The number of transitions on the SDO output depends on the output code, and thus changes with the analog input. The maximum value of f occurs when data output on the SDO change on every SCLK. SDO changing on every SCLK results in an output code of AAAh or 555h. For an output code of AAAh or 555h at a 1-MSPS throughput, the frequency of transitions on the SDO output is 6MHz.

For the current consumption to remain at the lowest possible value, keep the DVDD supply at the lowest permissible value and keep the capacitance on the SDO line as low as possible.

12.3 Optimizing Power Consumed by the Device

  • Keep the analog supply voltage (AVDD) as close as possible to the analog input voltage. Set AVDD to be greater than or equal to the analog input voltage of the device.
  • Keep the digital supply voltage (DVDD) at the lowest permissible value.
  • Reduce the load capacitance on the SDO output.
  • Run the device at the optimum throughput. Power consumption reduces with throughput.