SBAS778B June   2017  – August 2019 ADS1287

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Functional Block Diagram
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 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 Input and Multiplexer
      2. 8.3.2 Programmable Gain Amplifier (PGA)
      3. 8.3.3 Modulator
        1. 8.3.3.1 Modulator Overrange
      4. 8.3.4 Voltage Reference Inputs (REFP, REFN)
      5. 8.3.5 Digital Filter
        1. 8.3.5.1 Sinc Filter Stage
        2. 8.3.5.2 FIR Filter Stage
        3. 8.3.5.3 Group Delay and Step Response
          1. 8.3.5.3.1 Linear Phase Response
          2. 8.3.5.3.2 Minimum Phase Response
        4. 8.3.5.4 HPF Stage
      6. 8.3.6 Reset (RESET Pin and Reset Command)
      7. 8.3.7 Master Clock Input (CLK)
    4. 8.4 Device Functional Modes
      1. 8.4.1  Operational Mode
      2. 8.4.2  Chop Mode
      3. 8.4.3  Offset
      4. 8.4.4  Power-Down Mode
      5. 8.4.5  Standby Mode
      6. 8.4.6  Synchronization
        1. 8.4.6.1 Pulse-Sync Mode
        2. 8.4.6.2 Continuous-Sync Mode
      7. 8.4.7  Reading Data
        1. 8.4.7.1 Read-Data-Continuous Mode (RDATAC)
        2. 8.4.7.2 Stop-Read-Data-Continuous-Mode (SDATAC)
      8. 8.4.8  Conversion Data Format
      9. 8.4.9  Offset and Full-Scale Calibration Registers
        1. 8.4.9.1 OFC[2:0] Registers
        2. 8.4.9.2 FSC[2:0] Registers
      10. 8.4.10 Calibration Command
        1. 8.4.10.1 OFSCAL Command
        2. 8.4.10.2 GANCAL Command
      11. 8.4.11 User Calibration
    5. 8.5 Programming
      1. 8.5.1 Serial Interface
        1. 8.5.1.1 Chip Select (CS)
        2. 8.5.1.2 Serial Clock (SCLK)
        3. 8.5.1.3 Data Input (DIN)
        4. 8.5.1.4 Data Output (DOUT)
        5. 8.5.1.5 Serial Interface Timeout
        6. 8.5.1.6 Data Ready (DRDY)
      2. 8.5.2 Commands
        1. 8.5.2.1  WAKEUP: Wake Up Command
        2. 8.5.2.2  STANDBY: Standby Mode Command
        3. 8.5.2.3  SYNC: Synchronize ADC Conversions
        4. 8.5.2.4  RESET: Reset Command
        5. 8.5.2.5  RDATAC: Read Data Continuous Mode Command
        6. 8.5.2.6  SDATAC: Stop Read Data Continuous Mode Command
        7. 8.5.2.7  RDATA: Read Data Command
        8. 8.5.2.8  RREG: Read Register Data Command
        9. 8.5.2.9  WREG: Write Register Data Command
        10. 8.5.2.10 OFSCAL: Offset Calibration Command
        11. 8.5.2.11 GANCAL: Gain Calibration Command
    6. 8.6 Register Map
      1. 8.6.1 Register Descriptions
        1. 8.6.1.1 ID/CFG: ID, Configuration Register (address = 00h) [reset = x0h]
          1. Table 22. ID/CFG Register Field Descriptions
        2. 8.6.1.2 CONFIG0: Configuration Register 0 (address = 01h) [reset = 52h]
          1. Table 23. CONFIG0 Register Field Descriptions
        3. 8.6.1.3 CONFIG1: Configuration Register 1 (address = 02h) [reset = 08h]
          1. Table 24. CONFIG1 Register Field Descriptions
        4. 8.6.1.4 High-Pass Filter Corner Frequency (HPFx) Registers (address = 03h, 04h) [reset = 32h, 03h]
          1. Table 25. HPF0, HPF1 Registers Field Description
        5. 8.6.1.5 Offset Calibration (OFCx) Registers (address = 05h, 06h, 07h) [reset = 00h, 00h, 00h]
          1. Table 26. OFC0, OFC1, OFC2 Registers Field Description
        6. 8.6.1.6 Full-Scale Calibration (FSCx) Registers (address = 08h, 09h, 0Ah) [reset = 00h, 00h, 40h]
          1. Table 27. FSC0, FSC1, FSC2 Registers Field Description
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Geophone Application
      2. 9.2.2 Digital Interface
    3. 9.3 Initialization Set Up
  10. 10Power Supply Recommendations
    1. 10.1 Analog Power Supplies
    2. 10.2 Digital Power Supply
    3. 10.3 Power-Supply Sequence
  11. 11Layout
    1. 11.1 Layout Guidelines
  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 ADS1287 is a low-power, high-resolution analog-to-digital converter (ADC) intended for energy exploration, low-power seismic-data acquisition nodes, and other exacting applications that require very low power consumption. The converter provides 31-bit resolution over data rates 62.5 SPS to 1000 SPS, and programmable gains of 1 to 16 that expand the measurement resolution; see the Functional Block Diagram section.

The ADC consists of an input multiplexer (MUX), a low-noise complementary metal oxide semiconductor (CMOS) programmable gain amplifier (PGA), a fourth order delta-sigma (ΔΣ) modulator, an infinite impulse response (IIR) high-pass filter (HPF), a finite-impulse-response (FIR) low-pass filter (LPF), and an SPI-compatible serial interface used for both device configuration and conversion data readback.

The signal multiplexer selects between the external input or internal short (via 400-Ω resistors). The internal short is used for offset calibration and to verify the ADC offset and noise performance. The input multiplexer is followed by a programmable-gain, CMOS PGA, featuring low noise. The available PGA gains are 1 V/V, 2 V/V, 4 V/V, 8 V/V, and 16 V/V. The PGA is chopped to reduce 1/f noise and input offset voltage. The PGA output is routed to the modulator and to the CAPP and CAPN pins. An external 10-nF capacitor connected to these pins filters the modulator sampling pulses and provides the ADC antialias filter.

The inherently-stable, fourth-order, ΔΣ modulator measures the differential input signal VIN = V(AINP) – V(AINN) against the differential reference VREF = V(REFP) – V(REFN). The ADC requires an external 2.5-V voltage reference. The modulator output data are processed by an integrated digital filter to provide the final conversion result.

The digital filter consists of a sinc filter followed by a programmable-phase, FIR low-pass filter and programmable-frequency, IIR high-pass filter. The HPF removes DC and low-frequency components from the conversion result.

Programmable gain and offset data registers calibrate the conversion result to remove offset and gain errors.

The SYNC input pin synchronizes the ADC. Synchronization has two programable modes of operation: pulse-synchronization and continuous-synchronization that accepts a synchronizing-clock input. The RESET input resets the ADC including the register settings.

The PWDN input powers-down the ADC. The low-power STANDBY mode is engaged by software command.

RESET and SYNC control inputs are noise-resistant, Schmitt-trigger inputs to increase reliability in high-noise environments.

The ADC has an SPI-compatible serial interface. The interface is 4-wire and is used to read conversion data and to read and write device registers.

Power to the analog section is provided through AVDD and AVSS. DVDD is the digital and I/O supply. DVDD is sub-regulated to 1.8 V by an integrated, low-dropout regulator (LDO) to supply the digital core. The BYPAS pin is the LDO output and requires a 1-µF bypass capacitor.