SLDA058 March   2021 TUSS4470

 

  1.   Trademarks
  2. 1Review of Ultrasonic Sensing Range Performance Factors
    1. 1.1 Physical Parameters
    2. 1.2 Transducer Characteristics
    3. 1.3 AFE Device Configuration
  3. 2Methods Overview
    1. 2.1 Introduction
    2. 2.2 Hardware Configuration
      1. 2.2.1 Transducers
      2. 2.2.2 Experimental Setup: Air-Coupled Level Sensing
      3. 2.2.3 Experimental Setup: Water-Coupled Level Sensing
      4. 2.2.4 TUSS4470 EVM Hardware Configuration
      5. 2.2.5 TDC1000-C2000EVM Hardware Configuration
    3. 2.3 Firmware Configuration
      1. 2.3.1 TUSS4470 Power Configuration
      2. 2.3.2 TUSS4470 220 kHz Configuration
      3. 2.3.3 TDC1000 220kHz Configuration
      4. 2.3.4 TDC1000 220kHz Configuration
      5. 2.3.5 TDC1000 1 MHz
  4. 3Short Range Air-Coupled Test Results
    1. 3.1 TUSS4470
    2. 3.2 TDC1000
  5. 4Mid-Range Air-Coupled Test Results
    1. 4.1 TUSS4470
      1. 4.1.1 Concept
      2. 4.1.2 TUSS4470 35 V Results
    2. 4.2 TDC1000
  6. 5Short Range Water-Coupled Test Results
    1. 5.1 TUSS4470
    2. 5.2 TDC1000
  7. 6Resistive Damping Device Comparison
    1. 6.1 TUSS4470
    2. 6.2 TDC1000
  8. 7Summary
  9. 8References
  10.   A Appendix A
    1.     A.1 TUSS4470: Filter Capacitor Selection
    2.     A.2 TUSS4470: Shematic
  11.   B Appendix B
    1.     B.1 TDC1000 Misc.
    2.     B.2 TDC1000-C2000EVM Schematic

2.3.4 TDC1000 220kHz Configuration

Because the TDC1000's architecture is optimized for higher frequency liquid-coupled applications, utilizing the TDC1000 for air-coupled evaluation requires more fine tuning and patience than the TUSS4470. Table 2-4 provides recommended values as a starting point, allowing a ToF in the range 128 ✕ T0 up to 128 ✕ T0 + 1024 ✕ T0. Values are given in the GUI format, see the TDC1000-C2000EVM GUI and the TDC1000 data sheet programming section for corresponding register values. For a short ToF measurement time line graphic and T0, T1 definitions, see Appendix B.

Table 2-4 TDC1000 air-coupeld suggested evaluation FW setup
GUI Setting GUI Value Comments
TOF_MEAS_MODE 0 Measurement mode 0 for mono-static ToF measurements
Recieve Mode Single or Multi- Echo
CLOCKIN_DIV Div by 1 Set T0 with CLOCKIN_DIV
FORCE_SHORT_TOF Enabled The short ToF mode allows the common-mode voltage settling time (128 ✕ T0) to occur before the TX burst, so that the COMPIN signal will be less noisy and the listen period may be maximized.

TOF_TIMEOUT_CTRL

 1024 ✕ T0 This allows a maximum echo listen period of approximately 4.6 ms.
NUM_TX 10 - 15 pulses This is a good starting point for producing a strong return echo.
NUM_RX No RX Event Count This allows STOP signals to be generated for the duration of TOF_TIMEOUT_CTRL, avoiding ending the measurement due to an erroneously generated STOP.
PGA_GAIN 21 dB The maximum gain is recommended for air-coupled evaluation.
ECHO_QUAL_THLD -35 mV The most sensitive echo threshold setting may be necessary to trigger a STOP.
LNA_FB Resistive Required for transducers in this frequency range.
AUTOZERO_PERIOD 64 ✕ To In short ToF mode, this period occurs before the TX burst and can be adjusted if needed.
SHRT_TOF_BLNK_PRD 128 ✕ T0 This should allow plenty of time for noise coupled from the TX line to settle and have a clean COMPIN for viewing the return echo.

Evaluation Notes:

Signals of interest: START, STOP, COMPIN, TX.

For short range measurements, the blanking period may need to be shortened so the return echo can trigger a STOP. Depending on the transducer frequency, the transducer ringing decay could couple noise onto the COMPIN signal path causing a false STOP to be triggered at the beginning of the listen period. If this occurs, the blanking period can be set to mask this noise, or other means of ignoring a false STOP may be required at the designer's discretion. This is a good reason to set an unlimited NUM_RX event count for initial evaluation.