SBAS937B September   2018  – December 2018 ADS1278-SP

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements: SPI Format
    7. 7.7 Timing Requirements: Frame-Sync Format
    8. 7.8 Quality Conformance Inspection
    9. 7.9 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Sampling Aperture Matching
      2. 8.3.2  Frequency Response
        1. 8.3.2.1 High-Speed, Low-Power, And Low-Speed Modes
        2. 8.3.2.2 High-Resolution Mode
      3. 8.3.3  Phase Response
      4. 8.3.4  Settling Time
      5. 8.3.5  Data Format
      6. 8.3.6  Analog Inputs (AINP, AINN)
      7. 8.3.7  Voltage Reference Inputs (VREFP, VREFN)
      8. 8.3.8  Clock Input (CLK)
      9. 8.3.9  Mode Selection (MODE)
      10. 8.3.10 Synchronization (SYNC)
      11. 8.3.11 Power-Down (PWDN)
      12. 8.3.12 Format[2:0]
      13. 8.3.13 Serial Interface Protocols
      14. 8.3.14 SPI Serial Interface
        1. 8.3.14.1 SCLK
        2. 8.3.14.2 DRDY/FSYNC (SPI Format)
        3. 8.3.14.3 DOUT
        4. 8.3.14.4 DIN
      15. 8.3.15 Frame-Sync Serial Interface
        1. 8.3.15.1 SCLK
        2. 8.3.15.2 DRDY/FSYNC (Frame-Sync Format)
        3. 8.3.15.3 DOUT
        4. 8.3.15.4 DIN
      16. 8.3.16 DOUT Modes
        1. 8.3.16.1 TDM Mode
        2. 8.3.16.2 TDM Mode, Fixed-Position Data
        3. 8.3.16.3 TDM Mode, Dynamic Position Data
        4. 8.3.16.4 Discrete Data Output Mode
      17. 8.3.17 Daisy-Chaining
      18. 8.3.18 Modulator Output
      19. 8.3.19 Pin Test Using Test[1:0] Inputs
      20. 8.3.20 VCOM Output
    4. 8.4 Device Functional Modes
  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 Curve
  10. 10Power Supply Recommendations
  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 Community 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

8.1 Overview

The ADS1278-SP is a delta-sigma ADC consisting of eight independent converters that digitize eight input signals in parallel.

The converter is composed of two main functional blocks to perform the ADC conversions: the modulator and the digital filter. The modulator samples the input signal together with sampling the reference voltage to produce a 1-s density output stream. The density of the output stream is proportional to the analog input level relative to the reference voltage. The pulse stream is filtered by the internal digital filter where the output conversion result is produced.

In operation, the input signal is sampled by the modulator at a high rate (typically 64x higher than the final output data rate). The quantization noise of the modulator is moved to a higher frequency range where the internal digital filter removes it. Oversampling results in very low levels of noise within the signal passband.

Since the input signal is sampled at a very high rate, input signal aliasing does not occur until the input signal frequency is at the modulator sampling rate. This architecture greatly relaxes the requirement of external antialiasing filters because of the high modulator sampling rate.

The ADS1278-SP is an octal 24-bit, delta-sigma ADC. It offers the combination of outstanding dc accuracy and superior ac performance. Functional Block Diagram section shows the block diagram. The converter is comprised of eight advanced, 6th-order, chopper-stabilized, delta-sigma modulators followed by low-ripple, linear phase FIR filters. The modulators measure the differential input signal, VIN = (AINP – AINN), against the differential reference, VREF = (VREFP – VREFN). The digital filters receive the modulator signal and provide a low-noise digital output. To allow tradeoffs among speed, resolution, and power, four operating modes are supported:

High-Speed, High-Resolution, Low-Power, and Low-Speed. Table 15 summarizes the performance of each mode.

In High-Speed mode, the maximum data rate is 128 kSPS (when operating at 128 kSPS, Frame-Sync format must be used). In High-Resolution mode, the SNR = 111 dB (VREF = 3.0 V); in Low-Power mode, the power dissipation is 31 mW/channel; and in Low-Speed mode, the power dissipation is only 7 mW/channel at 10.5 kSPS. The digital filters can be bypassed, enabling direct access to the modulator output.

The ADS1278-SP is configured by simply setting the appropriate I/O pins—there are no registers to program. Data are retrieved over a serial interface that supports both SPI and Frame-Sync formats. The ADS1278-SP has a daisy-chainable output and the ability to synchronize externally, so it can be used conveniently in systems requiring more than eight channels.