SBAS946C April   2021  – September 2022 ADS127L11

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  Timing Requirements (1.65 V ≤ IOVDD ≤ 2 V)
    7. 6.7  Switching Characteristics (1.65 V ≤ IOVDD ≤ 2 V)
    8. 6.8  Timing Requirements (2 V < IOVDD ≤ 5.5 V)
    9. 6.9  Switching Characteristics (2 V < IOVDD ≤ 5.5 V)
    10. 6.10 Timing Diagrams
    11. 6.11 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1  Offset Error Measurement
    2. 7.2  Offset Drift Measurement
    3. 7.3  Gain Error Measurement
    4. 7.4  Gain Drift Measurement
    5. 7.5  NMRR Measurement
    6. 7.6  CMRR Measurement
    7. 7.7  PSRR Measurement
    8. 7.8  SNR Measurement
    9. 7.9  INL Error Measurement
    10. 7.10 THD Measurement
    11. 7.11 SFDR Measurement
    12. 7.12 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 (AINP, AINN)
        1. 8.3.1.1 Input Range
      2. 8.3.2 Reference Voltage (REFP, REFN)
        1. 8.3.2.1 Reference Voltage Range
      3. 8.3.3 Clock Operation
        1. 8.3.3.1 Internal Oscillator
        2. 8.3.3.2 External Clock
      4. 8.3.4 Modulator
      5. 8.3.5 Digital Filter
        1. 8.3.5.1 Wideband Filter
        2. 8.3.5.2 Low-Latency Filter (Sinc)
          1. 8.3.5.2.1 Sinc4 Filter
          2. 8.3.5.2.2 Sinc4 + Sinc1 Filter
          3. 8.3.5.2.3 Sinc3 Filter
          4. 8.3.5.2.4 Sinc3 + Sinc1 Filter
      6. 8.3.6 Power Supplies
        1. 8.3.6.1 AVDD1 and AVSS
        2. 8.3.6.2 AVDD2
        3. 8.3.6.3 IOVDD
        4. 8.3.6.4 Power-On Reset (POR)
        5. 8.3.6.5 CAPA and CAPD
      7. 8.3.7 VCM Output Voltage
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power-Scalable Speed Modes
      2. 8.4.2 Idle Mode
      3. 8.4.3 Standby Mode
      4. 8.4.4 Power-Down Mode
      5. 8.4.5 Reset
        1. 8.4.5.1 RESET Pin
        2. 8.4.5.2 Reset by SPI Register Write
        3. 8.4.5.3 Reset by SPI Input Pattern
      6. 8.4.6 Synchronization
        1. 8.4.6.1 Synchronized Control Mode
        2. 8.4.6.2 Start/Stop Control Mode
        3. 8.4.6.3 One-Shot Control Mode
      7. 8.4.7 Conversion-Start Delay Time
      8. 8.4.8 Calibration
        1. 8.4.8.1 OFFSET2, OFFSET1, OFFSET0 Calibration Registers (Addresses 9h, Ah, Bh)
        2. 8.4.8.2 GAIN2, GAIN1, GAIN0 Calibration Registers (Addresses 0Ch, 0Dh, 0Eh)
        3. 8.4.8.3 Calibration Procedure
    5. 8.5 Programming
      1. 8.5.1 Serial Interface (SPI)
        1. 8.5.1.1 Chip Select (CS)
        2. 8.5.1.2 Serial Clock (SCLK)
        3. 8.5.1.3 Serial Data Input (SDI)
        4. 8.5.1.4 Serial Data Output/Data Ready (SDO/DRDY)
      2. 8.5.2 SPI Frame
      3. 8.5.3 SPI CRC
      4. 8.5.4 Register Map CRC
      5. 8.5.5 Full-Duplex Operation
      6. 8.5.6 Device Commands
        1. 8.5.6.1 No-Operation
        2. 8.5.6.2 Read Register Command
        3. 8.5.6.3 Write Register Command
      7. 8.5.7 Read Conversion Data
        1. 8.5.7.1 Conversion Data
        2. 8.5.7.2 Data Ready
          1. 8.5.7.2.1 DRDY
          2. 8.5.7.2.2 SDO/DRDY
          3. 8.5.7.2.3 DRDY Bit
          4. 8.5.7.2.4 Clock Counting
        3. 8.5.7.3 STATUS Header
      8. 8.5.8 Daisy-Chain Operation
      9. 8.5.9 3-Wire SPI Mode
        1. 8.5.9.1 3-Wire SPI Mode Frame Reset
    6. 8.6 Registers
      1. 8.6.1  DEV_ID Register (Address = 0h) [reset = 00h]
      2. 8.6.2  REV_ID Register (Address = 1h) [reset = xxh]
      3. 8.6.3  STATUS Register (Address = 2h) [reset = x1100xxxb]
      4. 8.6.4  CONTROL Register (Address = 3h) [reset = 00h]
      5. 8.6.5  MUX Register (Address = 4h) [reset = 00h]
      6. 8.6.6  CONFIG1 Register (Address = 5h) [reset = 00h]
      7. 8.6.7  CONFIG2 Register (Address = 6h) [reset = 00h]
      8. 8.6.8  CONFIG3 Register (Address = 7h) [reset = 00h]
      9. 8.6.9  CONFIG4 Register (Address = 8h) [reset = 00h]
      10. 8.6.10 OFFSET2, OFFSET1, OFFSET0 Registers (Addresses = 9h, Ah, Bh) [reset = 00h, 00h, 00h]
      11. 8.6.11 GAIN2, GAIN1, GAIN0 Registers (Addresses = Ch, Dh, Eh) [reset = 40h, 00h, 00h]
      12. 8.6.12 CRC Register (Address = Fh) [reset = 00h]
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 SPI Operation
      2. 9.1.2 Input Driver
      3. 9.1.3 Antialias Filter
      4. 9.1.4 Reference Voltage
      5. 9.1.5 Simultaneous-Sampling Systems
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Documentation Support
      1. 10.1.1 Related Documentation
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.3.5.1 Wideband Filter

The wideband filter is a multistage FIR filter design featuring linear phase response, low pass-band ripple, narrow transition band, and high stop-band attenuation. Because of the superior frequency response characteristics, the filter is well suited for measuring ac signals. The ADC provides eight programmable oversampling ratios (OSR) and two speed modes, offering a range of data rate and resolution to select from.

Figure 8-8 through Figure 8-12 illustrate the frequency response of the wideband filter. Figure 8-8 shows the pass-band ripple. Figure 8-9 shows the detailed frequency response at the transition band.

GUID-20201006-CA0I-WVMP-H84L-06HR4S54JSXP-low.gifFigure 8-8 Wideband Filter Pass-Band Ripple
GUID-20201006-CA0I-CLXP-2CSG-SR2JZ8Q6LDVM-low.gifFigure 8-9 Wideband Filter Transition Band

Figure 8-10 shows the frequency response to fDATA for OSR ≥ 64. The stop band begins at fDATA / 2 to prevent aliasing at the Nyquist frequency. Figure 8-11 shows the stop-band attenuation to fMOD for OSR = 32. In the stop-band region, out-of-band input frequencies intermodulate with multiples of the chop frequency at fMOD / 32, creating a pattern of response peaks that exceed the stop-band attenuation of the digital filter. The width of the response peaks is twice the filter bandwidth. Stop-band attenuation is improved when used in conjunction with an antialias filter at the ADC input. See the Section 9.2 section for details of a fourth-order antialias filter.

GUID-20201006-CA0I-TJTC-PQG1-NQMZLTMTQTGT-low.gif
OSR ≥ 64
Figure 8-10 Wideband Filter Frequency Response
OSR = 32
Figure 8-11 Wideband Filter Stop-Band Attenuation

Figure 8-12 shows the filter response centered around fMOD. As shown, the filter response repeats at fMOD. If not removed by an antialiasing filter, input frequencies at fMOD appear as aliased frequencies in the pass band. Aliasing also occurs with input frequencies occurring at multiples of fMOD. These frequency bands are defined by:

Equation 16. Alias frequency bands: (N · fMOD) ± fBW

where:

  • N = 1, 2, 3, and so on
  • fMOD = Modulator sampling frequency
  • fBW = Filter bandwidth

Figure 8-12 Wideband Filter Frequency Response Centered at fMOD

The group delay of the filter is the time for an input signal to propagate from the input to the output of the filter. Because the filter is a linear-phase design, the envelope of a complex input signal is undistorted by the filter. The group delay (expressed in units of time) is constant versus frequency equal to the value = 34 / fDATA. After a step input is applied, fully settled data occur at 68 data periods later. Figure 8-13 illustrates the filter group delay (34 / fDATA) and the settling time to a step input (68 / fDATA).

Figure 8-13 Wideband Filter Step Response

The digital filter is restarted when the ADC is synchronized. The ADC suppresses the first 68 conversion periods until the filter is fully settled. There is no need to discard data after synchronization. The time of data suppression is the conversion latency time as listed in the latency time column of Table 8-3. A 0.4-μs fixed overhead time is incurred for all data rates. If a step input occurs asynchronous to the conversion period without synchronizing, then the next 69 conversions are partially settled data.

Table 8-3 Wideband Filter Characteristics
OSR DATA RATE (kSPS) –0.1-dB FREQUENCY (kHz) –3-dB FREQUENCY (kHz) LATENCY TIME (µs)(1)
HIGH-SPEED MODE (fCLK = 25.6 MHz)
32 400 165 174.96 170.6
64 200 82.5 87.48 340.6
128 100 41.25 43.74 680.6
256 50 20.625 21.87 1360.6
512 25 10.312 10.935 2720.6
1024 12.5 5.156 5.467 5440.6
2014 6.25 2.578 2.734 10880.6
4096 3.125 1.289 1.367 21760.6
LOW-SPEED MODE (fCLK = 3.2 MHz)
32 50 20.625 21.87 1364.8
64 25 10.312 10.935 2724.8
128 12.5 5.156 5.467 5444.8
256 6.25 2.578 2.734 10884.8
512 3.125 1.289 1.367 21764.8
1024 1.5625 0.645 0.683 43524.8
2048 0.78125 0.322 0.342 87044.8
4096 0.390625 0.161 0.171 174084.8
(1) Latency time increases 8 / fCLK (µs) when analog input buffers are enabled.