SNOSCZ7B December   2015  – April 2024 LDC0851

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Interface Voltage Levels
    7. 5.7 Timing Requirements
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Basic Operation Mode
      2. 6.3.2 Threshold Adjust Mode
      3. 6.3.3 Setting the Threshold Adjust Values
      4. 6.3.4 Hysteresis
      5. 6.3.5 Conversion Time
      6. 6.3.6 Power-Up Conditions
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown Mode
      2. 6.4.2 Active Mode
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Sensor Design
        1. 7.1.1.1 Sensor Frequency
        2. 7.1.1.2 Sensor Design Procedure
    2. 7.2 Typical Application
      1. 7.2.1 Event Counting
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curves
      2. 7.2.2 Coarse Position Sensing
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
        3. 7.2.2.3 Application Curves
      3. 7.2.3 Low Power Operation
        1. 7.2.3.1 Design Requirements
        2. 7.2.3.2 Detailed Design Procedure
        3. 7.2.3.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
        1. 7.4.2.1 Side by Side Coils
        2. 7.4.2.2 Stacked Coils
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.3.2 Detailed Design Procedure

In order to achieve 10 year lifetime out of a single CR2032 battery, the enable pin (EN) of the LDC0851 can be duty cycled to achieve a low average supply current. Refer to Figure 7-7 to see the three different states of LDC0851 supply current during duty cycle operation. The sum of the Standby, Ramp, and On currents can be used to calculate the average supply current of the LDC0851, which needs to be below 2.5 µA to achieve a 10 year lifetime from a 220 mAh CR2032 battery.

The average supply current can be calculated in the following steps:

  1. Select desired system sample rate (ƒSAMPLE) based on the given application. In this example, ƒSAMPLE is 1 sample per second.
  2. Select the sensor characteristics (ƒSENSOR, LSENSOR, CSENSOR) based on conversion time and current consumption.
    1. ƒSENSOR should be increased as much as possible to minimize the conversion time. 10 MHz is chosen as a starting point.
    2. LSENSOR should be increased as much as possible to decrease the sensor current (ISENSOR). Based on a reasonable PCB area, 10 µH is a good starting point.
    3. CSENSOR is calculated to be 34.5 pF from Equation 8 using the inputs above. This makes CTOTAL equal to 50.5 pF which meets the requirement of greater than 33 pF to be inside the design space.
  3. Calculate the average active current:
    Equation 10. GUID-DA1D91D4-F87F-41D0-B9AD-B0ABD0D0ACD9-low.gif

    • where:

    • ƒSAMPLE is the number of samples per second given from step 1. In this example, ƒSAMPLE is equal to 1.
    • tCONVERSION is calculated from Equation 2 to give a conversion time of 433 µs.
    • IDD is the total active supply current given by Equation 5 to be 1.587 mA.
    • ION is the active current consumed by the LDC0851 which comes to be 1.37 µA.
  4. Calculate the average ramp current:
    Equation 11. GUID-C4B7B021-3F9B-409D-8D7E-B8AD2BE10A95-low.gif

    • where:

    • ƒSAMPLE is the number of samples per second given from step 1. In this example, ƒSAMPLE is equal to 1.
    • tAMT is the active mode transition time given in the electrical table as typically 450µs.
    • IDD is the total active supply current given by Equation 5 to be 1.587 mA.
    • IRAMP is the current consumed by the LDC0851 before a conversion has started which comes to be 0.357 µA.
  5. Calculate the average standby current:
    Equation 12. GUID-CA4AE080-F643-41FC-904E-40CAF598D88B-low.gif

    • where:

    • ƒSAMPLE is the number of samples per second given from step 1. In this example, ƒSAMPLE is equal to 1.
    • tAMT is the active mode transition time given in the electrical table as typically 450µs.
    • tCONVERSION is calculated from Equation 2 to give a conversion time of 433 µs.
    • ISD is the shutdown current of the LDC0851 given in the electrical table as typically 140nA.
    • IOFF is the standby current of the LDC0851 which comes to be 0.140 µA.
  6. Calculate the total average supply current:
    Equation 13. GUID-AC569A66-4940-466A-AD13-CFC9D797D566-low.gif

    • where:

    • ION is the active supply current given from Equation 10 to be 1.37 µA.
    • IRAMP is the ramp current given by Equation 11 to be 0.357 µA.
    • IOFF is the standby current given by Equation 12 to be 0.140 µA.
    • IAVG is the average supply current consumed per second which comes to 1.867 µA.
  7. Finally the lifetime of the battery can be calculated:
    Equation 14. GUID-FEA12A74-A029-4B10-B291-F59D89D76065-low.gif

    • where:

    • Battery Capacity is the amount of charge x time that the battery can hold in mAh. This example uses a CR2032 battery with 220 mAh.
    • IAVG is the value reported in Equation 13 to be 1.867 µA.
    • Battery Lifetime (years) is how long the battery will last reported in years which comes out to be 13.5 years with the inputs from above.

For example, using a sensor frequency of 10 MHz, sensor inductance of 10 µH, and 1 sample per second yields a lifetime of 13.5 years for a single CR2032 battery.