SLVSKW2 January   2026 ADS1278QML-SP

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 Quality Conformance Inspection
    7. 5.7 Timing Requirements: SPI Format
    8. 5.8 Timing Requirements: Frame-Sync Format
    9. 5.9 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  Sampling Aperture Matching
      2. 6.3.2  Frequency Response
        1. 6.3.2.1 High-Speed, Low-Power, And Low-Speed Modes
        2. 6.3.2.2 High-Resolution Mode
      3. 6.3.3  Phase Response
      4. 6.3.4  Settling Time
      5. 6.3.5  Data Format
      6. 6.3.6  Analog Inputs (AINP, AINN)
      7. 6.3.7  Voltage Reference Inputs (VREFP, VREFN)
      8. 6.3.8  Clock Input (CLK)
      9. 6.3.9  Mode Selection (MODE)
      10. 6.3.10 Synchronization (SYNC)
      11. 6.3.11 Power-Down ( PWDN)
      12. 6.3.12 Format[2:0]
      13. 6.3.13 Serial Interface Protocols
      14. 6.3.14 SPI Serial Interface
        1. 6.3.14.1 SCLK
        2. 6.3.14.2 DRDY/FSYNC (SPI Format)
        3. 6.3.14.3 DOUT
        4. 6.3.14.4 DIN
      15. 6.3.15 Frame-Sync Serial Interface
        1. 6.3.15.1 SCLK
        2. 6.3.15.2 DRDY/FSYNC (Frame-Sync Format)
        3. 6.3.15.3 DOUT
        4. 6.3.15.4 DIN
      16. 6.3.16 DOUT Modes
        1. 6.3.16.1 TDM Mode
        2. 6.3.16.2 TDM Mode, Fixed-Position Data
        3. 6.3.16.3 TDM Mode, Dynamic Position Data
        4. 6.3.16.4 Discrete Data Output Mode
      17. 6.3.17 Daisy-Chaining
      18. 6.3.18 Modulator Output
      19. 6.3.19 Pin Test Using Test[1:0] Inputs
      20. 6.3.20 VCOM Output
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Application Curve
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Community Resources
    3. 8.3 Trademarks
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

6.3.7 Voltage Reference Inputs (VREFP, VREFN)

The voltage reference for the ADS1278QML-SP ADC is the differential voltage between VREFP and VREFN: VREF = (VREFP – VREFN). The voltage reference is common to all channels. The reference inputs use a structure similar to that of the analog inputs with the equivalent circuitry on the reference inputs shown in Figure 6-13. As with the analog inputs, the load presented by the switched capacitor can be modeled with an effective impedance, as shown in Figure 6-14. However, the reference input impedance depends on the number of active (enabled) channels in addition to fMOD. As a result of the change of reference input impedance caused by enabling and disabling channels, the regulation and setting time of the external reference must be noted, so as not to affect the readings.

ADS1278QML-SP Equivalent Reference Input CircuitryFigure 6-13 Equivalent Reference Input Circuitry
ADS1278QML-SP Effective Reference ImpedanceFigure 6-14 Effective Reference Impedance

ESD diodes protect the reference inputs. To keep these diodes from turning on, make sure the voltages on the reference pins do not go below AGND by more than 0.4V, and likewise do not exceed AVDD by 0.4V. If these conditions are possible, external Schottky clamp diodes or series resistors can be required to limit the input current to safe values (see the Absolute Maximum Ratings table).

Note that the valid operating range of the reference inputs is limited to the following parameters:

–0.1V ≤ VREFN ≤ +0.1V

VREFN + 0.5V ≤ VREFP ≤ AVDD + 0.1V