SLASEJ4C April   2017  – February 2023 PGA460

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  Internal Supply Regulators Characteristics
    6. 6.6  Transducer Driver Characteristics
    7. 6.7  Transducer Receiver Characteristics
    8. 6.8  Analog to Digital Converter Characteristics
    9. 6.9  Digital Signal Processing Characteristics
    10. 6.10 Temperature Sensor Characteristics
    11. 6.11 High-Voltage I/O Characteristics
    12. 6.12 Digital I/O Characteristics
    13. 6.13 EEPROM Characteristics
    14. 6.14 Timing Requirements
    15. 6.15 Switching Characteristics
    16. 6.16 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Power-Supply Block
      2. 7.3.2  Burst Generation
        1. 7.3.2.1 Using Center-Tap Transformer
        2. 7.3.2.2 Direct Drive
        3. 7.3.2.3 Other Configurations
      3. 7.3.3  Analog Front-End
      4. 7.3.4  Digital Signal Processing
        1. 7.3.4.1 Ultrasonic Echo—Band-Pass Filter
        2. 7.3.4.2 Ultrasonic Echo–Rectifier, Peak Hold, Low-Pass Filter, and Data Selection
        3. 7.3.4.3 Ultrasonic Echo—Nonlinear Scaling
        4. 7.3.4.4 Ultrasonic Echo—Threshold Data Assignment
        5. 7.3.4.5 Digital Gain
      5. 7.3.5  System Diagnostics
        1. 7.3.5.1 Device Internal Diagnostics
      6. 7.3.6  Interface Description
        1. 7.3.6.1 Time-Command Interface
          1. 7.3.6.1.1 RUN Commands
          2. 7.3.6.1.2 CONFIGURATION/STATUS Command
        2. 7.3.6.2 USART Interface
          1. 7.3.6.2.1 USART Asynchronous Mode
            1. 7.3.6.2.1.1 Sync Field
            2. 7.3.6.2.1.2 Command Field
            3. 7.3.6.2.1.3 Data Fields
            4. 7.3.6.2.1.4 Checksum Field
            5. 7.3.6.2.1.5 PGA460 UART Commands
            6. 7.3.6.2.1.6 UART Operations
              1. 7.3.6.2.1.6.1 No-Response Operation
              2. 7.3.6.2.1.6.2 Response Operation (All Except Register Read)
              3. 7.3.6.2.1.6.3 Response Operation (Register Read)
            7. 7.3.6.2.1.7 Diagnostic Field
            8. 7.3.6.2.1.8 USART Synchronous Mode
          2. 7.3.6.2.2 One-Wire UART Interface
          3. 7.3.6.2.3 Ultrasonic Object Detection Through UART Operations
        3. 7.3.6.3 In-System IO-Pin Interface Selection
      7. 7.3.7  Echo Data Dump
        1. 7.3.7.1 On-Board Memory Data Store
        2. 7.3.7.2 Direct Data Burst Through USART Synchronous Mode
      8. 7.3.8  Low-Power Mode
        1. 7.3.8.1 Time-Command Interface
        2. 7.3.8.2 UART Interface
      9. 7.3.9  Transducer Time and Temperature Decoupling
        1. 7.3.9.1 Time Decoupling
        2. 7.3.9.2 Temperature Decoupling
      10. 7.3.10 Memory CRC Calculation
      11. 7.3.11 Temperature Sensor and Temperature Data-Path
      12. 7.3.12 TEST Pin Functionality
    4. 7.4 Device Functional Modes
    5. 7.5 Programming
      1. 7.5.1 UART and USART Communication Examples
    6. 7.6 Register Maps
      1. 7.6.1 EEPROM Programming
      2. 7.6.2 Register Map Partitioning and Default Values
      3. 7.6.3 REGMAP Registers
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Transducer Types
    2. 8.2 Typical Applications
      1. 8.2.1 Transformer-Driven Method
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Transducer Driving Voltage
          2. 8.2.1.2.2 Transducer Driving Frequency
          3. 8.2.1.2.3 Transducer Pulse Count
          4. 8.2.1.2.4 Transformer Turns Ratio
          5. 8.2.1.2.5 Transformer Saturation Current and Main Voltage Rating
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Direct-Driven (Transformer-Less) Method
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  9. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  10. 10Mechanical, Packaging, and Orderable Information

7.3.3 Analog Front-End

The analog front-end (AFE) in the PGA460 device, shown in #X1316, receives the reflected echo from the object, amplifies it, and feeds it into a digital signal processing (DSP) data path for echo detection. Because the received echo signal can vary amplitude (in millivolts for near objects and in microvolts for far objects), the first AFE stage is a very low-noise balanced amplifier with a predetermined fixed gain followed by a variable gain-stage amplifier with configurable gain from 32 dB to 90 dB. The amplified echo signal is converted into a digital signal by a 12-bit analog-to-digital converter (ADC) and fed to a DSP processing block for further evaluation and time-of-flight measurement.

The PGA460 AFE implements system diagnostics for sensing element (transducer) monitoring during the burst and decay stage of the echo recording process in a way of measuring the maximum achieved voltage at the transducer node and the frequency of oscillation at the transducer node. For more information on these diagnostics, see the GUID-BC9FDDC3-E4C4-4B97-827D-A2FCEED52928.html#TITLE-SLASEC8X133 section.

GUID-C7298CA4-8EC7-4AD5-AA1F-AB7FE527B4D1-low.gifFigure 7-3 Analog Front-End

The variable gain amplifier in the AFE implements a time-varying gain feature which allows the user to set different static gains and also specify a gain profile for the echo listening process (echo record time). This feature allows for a uniform amplification of echo signals from objects at different distances without saturating the ADC. As an example, for closer objects, gain can be programmed lower initially in time and then increased during the recording time to detect farther objects which have a very small echo signal. This feature helps in attaining sufficient SNR after ADC conversion for all distances for accurate time of flight measurement.

The time-varying gain parameters are stored in the EEPROM memory and characterized by:

  • The initial fixed-gain parameter, GAIN_INIT.
  • A time-varying gain start-time value stored in the TVGAIN0 register.
  • An array of 5 gain-varying cross points placed in the TVGAIN0 to TVGAIN6 registers.

#X2707 shows an example plot of the time-varying gain.

GUID-412BB63E-664E-44EC-83BA-241C4A574996-low.gifFigure 7-4 Time-Varying Gain Assignment Example

The time value, TVG start time, is expressed in terms of absolute time, and all following TVG point times (TVG_Tx parameters) are expressed as a delta time between the current and previous point. All gain values are expressed in an absolute gain value in dB and are unrelated from each other. The final gain setting of TVG Point 5 (TVG_G5) will be kept constant until the end of the echo record time. The time-varying gain assignment is the same for both presets. A linear interpolation scheme is used to calculate gain between two TVG points. The AFE gain resolution is 0.5 dB typical.

Note:

The time-varying gain changes during the recording are applied only on the record cycle that follows. If the TVGAIN[0:6] registers programmed to 0x00, the time-varying gain function of the PGA460 device is disabled and a fixed gain defined by the INIT_GAIN register is applied. In this case, changing the INIT_GAIN register changes the gain of AFE during the recording.

The offset on the time-varying gain is controlled through the two AFE_GAIN_RNG bits in DECPL_TEMP register. For each of the four settings as defined in the GUID-ED773D30-2D5D-4A9D-B0E9-278B351A9705.html#TITLE-SLASEC8X3442 section, the gain can be varied from 0 to 32 dB added on top of the offset.