SBAS350G June   2005  – January 2021 ADS1232 , ADS1234

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1 Noise Performance
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Analog Inputs (AINPX, AINNX)
      2. 8.3.2  Temperature Sensor (ADS1232 Only)
      3. 8.3.3  Low-Noise PGA
        1. 8.3.3.1 PGA Bypass Capacitor
      4. 8.3.4  Voltage Reference Inputs (REFP, REFN)
      5. 8.3.5  Clock Sources
      6. 8.3.6  Digital Filter Frequency Response
      7. 8.3.7  Settling Time
      8. 8.3.8  Data Rate
      9. 8.3.9  Data Format
      10. 8.3.10 Data Ready and Data Output (DRDY/DOUT)
      11. 8.3.11 Serial Clock Input (SCLK)
      12. 8.3.12 Data Retrieval
    4. 8.4 Device Functional Modes
      1. 8.4.1 Offset Calibration Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Standby Mode With Offset-Calibration
      4. 8.4.4 Power-Down Mode
      5. 8.4.5 Power-Up Sequence
      6. 8.4.6 Summary of Serial Interface Waveforms
  9. 9 Application and Implementation
    1. 9.1 Application Information
    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
    1. 10.1 Power-Supply Decoupling
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Receiving Notification of Documentation Updates
    2. 12.2 Support Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.3.4 Voltage Reference Inputs (REFP, REFN)

The voltage reference used by the modulator is generated from the voltage difference between pins REFP and REFN: VREF = V(REFP) – V(REFN). The reference inputs use a structure similar to that of the analog inputs. In order to increase the reference input impedance, a switching buffer circuitry is used to reduce the input equivalent capacitance. The reference drift and noise impact ADC performance. In order to achieve best results, pay close attention to the reference noise and drift specifications. A simplified diagram of the circuitry on the reference inputs is shown in Figure 8-3. The switches and capacitors can be modeled with an effective impedance of:

Equation 3. GUID-7B1B9FCF-42FD-47C1-B300-676D8A2103F7-low.gif

where

  • fMOD = modulator sampling frequency = fCLK / 64 = (76.8 kHz)
  • CBUF = input capacitance of the buffer

For the ADS123x:

Equation 3. GUID-42DB9854-4238-41B8-A0C3-371ABB455ADE-low.gif
GUID-C0DE0509-A8C7-4A40-982B-7C1F6025274E-low.gifFigure 8-3 Simplified Reference Input Circuitry

ESD diodes protect the reference inputs. To prevent these diodes from turning on, make sure the voltages on the reference pins do not go below AGND by more than 100 mV; and likewise, do not exceed AVDD by 100 mV:

AGND – 100 mV < V(REFP) or V(REFN) < AVDD + 100 mV