SBAS444E May   2009  – December 2024

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5.   Device Comparison Table
  6. 4 Pin Configuration and Functions
  7. 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 Timing Requirements: I2C
    7. 5.7 Typical Characteristics
  8. 6 Parameter Measurement Information
    1. 6.1 Noise Performance
  9. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Multiplexer
      2. 7.3.2 Analog Inputs
      3. 7.3.3 Full-Scale Range (FSR) and LSB Size
      4. 7.3.4 Voltage Reference
      5. 7.3.5 Oscillator
      6. 7.3.6 Output Data Rate and Conversion Time
      7. 7.3.7 Digital Comparator (ADS1114 and ADS1115 Only)
      8. 7.3.8 Conversion Ready Pin (ADS1114 and ADS1115 Only)
      9. 7.3.9 SMbus Alert Response
    4. 7.4 Device Functional Modes
      1. 7.4.1 Reset and Power-Up
      2. 7.4.2 Operating Modes
        1. 7.4.2.1 Single-Shot Mode
        2. 7.4.2.2 Continuous-Conversion Mode
      3. 7.4.3 Duty Cycling For Low Power
    5. 7.5 Programming
      1. 7.5.1 I2C Interface
        1. 7.5.1.1 I2C Address Selection
        2. 7.5.1.2 I2C General Call
        3. 7.5.1.3 I2C Speed Modes
      2. 7.5.2 Target Mode Operations
        1. 7.5.2.1 Receive Mode
        2. 7.5.2.2 Transmit Mode
      3. 7.5.3 Writing To and Reading From the Registers
      4. 7.5.4 Data Format
  10. 8 Registers
    1. 8.1 Register Map
      1. 8.1.1 Address Pointer Register (address = N/A) [reset = N/A]
      2. 8.1.2 Conversion Register (P[1:0] = 00b) [reset = 0000h]
      3. 8.1.3 Config Register (P[1:0] = 01b) [reset = 8583h]
      4. 8.1.4 Lo_thresh (P[1:0] = 10b) [reset = 8000h] and Hi_thresh (P[1:0] = 11b) [reset = 7FFFh] Registers
  11. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Basic Connections
      2. 9.1.2 Single-Ended Inputs
      3. 9.1.3 Input Protection
      4. 9.1.4 Unused Inputs and Outputs
      5. 9.1.5 Analog Input Filtering
      6. 9.1.6 Connecting Multiple Devices
      7. 9.1.7 Quick-Start Guide
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Shunt Resistor Considerations
        2. 9.2.2.2 Operational Amplifier Considerations
        3. 9.2.2.3 ADC Input Common-Mode Considerations
        4. 9.2.2.4 Resistor (R1, R2, R3, R4) Considerations
        5. 9.2.2.5 Noise and Input Impedance Considerations
        6. 9.2.2.6 First-Order RC Filter Considerations
        7. 9.2.2.7 Circuit Implementation
        8. 9.2.2.8 Results Summary
      3. 9.2.3 Application Curves
  12. 10Power Supply Recommendations
    1. 10.1 Power-Supply Sequencing
    2. 10.2 Power-Supply Decoupling
  13. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  14. 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
  15. 13Revision History
  16. 14Mechanical, Packaging, and Orderable Information

9.2.2.7 Circuit Implementation

Table 9-2 shows the chosen values for this design.

Table 9-2 Parameters
PARAMETERVALUE
VCM2.5V
FSR of ADC±0.256V
Output data rate250SPS
R1, R31kΩ(1)
R2, R45kΩ(1)
R5, R6100Ω(1)
CDIFF0.22µF
CCM1, CCM20.022µF
(1) 1% precision resistors used.

Using Equation 7, if VSHUNT ranges from –50mV to +50mV, the application circuit produces a differential voltage ranging from –0.250V to +0.250V across the ADC inputs. The ADC is therefore configured at an FSR of ±0.256V to maximize the dynamic range of the ADC.

The –3dB cutoff frequencies of the differential low-pass filter and the common-mode low-pass filters are set at 3.6kHz and 0.36kHz, respectively.

RSHUNT typically ranges from 0.01mΩ to 100mΩ. Therefore, if R1 = R3 = 1kΩ, a good trade-off exists between the circuit input impedance and input referred resistor noise as explained in the Noise and Input Impedance Considerations section.

A simple resistor divider followed by a buffer amplifier is used to generate VCM of 2.5V from a 5V supply.