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

8.3.18 Modulator Output

The ADS1278-SP incorporates a 6th-order, single-bit, chopper-stabilized modulator followed by a multi-stage digital filter that yields the conversion results. The data stream output of the modulator is available directly, bypassing the internal digital filter. The digital filter is disabled, reducing the DVDD current, as shown in Table 13. In this mode, an external digital filter implemented in an ASIC, FPGA, or similar device is required. To invoke the modulator output, tie FORMAT[2:0], as shown in Figure 80. DOUT[8:1] then becomes the modulator data stream outputs for each channel and SCLK becomes the modulator clock output. The DRDY/FSYNC pin becomes an unused output and can be ignored. The normal operation of the Frame-Sync and SPI interfaces is disabled, and the functionality of SCLK changes from an input to an output, as shown in Figure 80.

Table 13. Modulator Output Clock Frequencies

MODE
[1:0]		 CLKDIV MODULATOR CLOCK OUTPUT (SCLK) DVDD (mA)
00 1 fCLK / 4 8
01 1 fCLK / 4 7
10 1 fCLK / 8 4
0 fCLK / 4 4
11 1 fCLK / 40 1
0 fCLK / 8 1
ADS1278-SP ai_modout_bas367.gifFigure 80. Modulator Output

In modulator output mode, the frequency of the modulator clock output (SCLK) depends on the mode selection of the ADS1278-SP. Table 13 lists the modulator clock output frequency and DVDD current versus device mode.

Figure 81 shows the timing relationship of the modulator clock and data outputs.

The data output is a modulated 1s density data stream. When VIN = +VREF, the 1s density is approximately 80% and when VIN = –VREF, the 1s density is approximately 20%.

ADS1278-SP ai_modout_time_bas367.gifFigure 81. Modulator Output Timing