SLAAES9 March   2025 MSP430FR5043 , MSP430FR6005 , MSP430FR6007 , MSP430FR6043 , MSP430FR6045 , MSP430FR6047

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Flow Meter Measurement Theory
    1. 2.1 TOF Measurement Algorithm Implementation
      1. 2.1.1 AbsTOF Calculation Method – Lobe
      2. 2.1.2 AbsTOF Calculation Method – Hilbert Wide
      3. 2.1.3 dTOF Calculation Method - Cross-Correlation
        1. 2.1.3.1 Get a High-Precision dTOF Result
        2. 2.1.3.2 Optimization in Cross-Correlation Method
    2. 2.2 Differences between ADC Approach and TDC Approach
  6. 3MSP430 MCUs for USS Application
    1. 3.1 USS Module
    2. 3.2 Differences Between USS and USS_A Module
    3. 3.3 Software Implementation on MSP430 MCUs
  7. 4Hardware Design Flow
    1. 4.1 Schematics
      1. 4.1.1 Water Meter Schematic – MSP430FR6047 and MSP430FR6007
      2. 4.1.2 Water Meter Schematic – MSP430FR6043 and MSP430FR5043
      3. 4.1.3 Gas Meter Schematic – MSP430FR6043 and MSP430FR5043
    2. 4.2 PCB Layout Guide
  8. 5Software Design Guide
    1. 5.1 USS Demo Projects and Related Resources
    2. 5.2 Demo Project Instruction
      1. 5.2.1 Files in Demo Project
      2. 5.2.2 Properties Setting in Demo Project
  9. 6Summary
  10. 7References

4.1.3 Gas Meter Schematic – MSP430FR6043 and MSP430FR5043

For gas meter applications, use an external AFE circuit with MSP USS MCUs for the hardware design. For more details, refer to the TIDM-02003.

There are several points which need to be highlighted.

  1. For evaluating gas meter applications on EVM430-FR6043 board, only use the channel CH0 for both UPS and DNS signal path. The analog switch U7 and U8 are used to switch the direction on the UPS and DNS signal. This can give a better ZFD performance compare to using both CH0 and CH1 channels.
  2. Note that R10, R13 and R14 are essential for the hardware design. Do not forget these.
  3. The U9 SN74LVC2T45 is a voltage level shifting component. This level shifts the excitation signal voltage to 5V, and improves the measurement performance in strict test environments. By default, the 5V LDO is bypassed on the EVM board. Users can add a jumper on the JP1 5VENA, and move the jumper on the JP2 from 3.3VTX to 5VTX. Find the predefined symbols in the Project Properties->Build->MSP430 Compiler->Predefined Symbols. Then, change the predefined symbol __AFE_EXT_3v3__ to __AFE_EXT_5v0__ to enable the 5V excitation function.

    Users can also remove this U9 on the board. The reference circuit without the U9 is shown in Figure 4-2. Note that R47 and R49 are kept in the circuit.

    A Schematic Without Level Shifter Figure 4-2 A Schematic Without Level Shifter
  4. For the U10 OPA836, TI is recommends to use the same circuit as shown in the EVM board. The bandwidth -3dB at 584kHz is from the TINA simulation based on the Low-Power Applications and the Effects of Resistor Values on Bandwidth section of the OPAx836 Very-Low-Power, Rail-to-Rail Out, Negative Rail In, Voltage-Feedback Operational Amplifiers data sheet. This circuit is a general recommendation circuit for both 200kHz, 400kHz and 500kHz transducers. Users can change the circuit based on the design.

    R65, R67, R66 and C45 provide a bias voltage for the OPA IN+ input. Users can also find the R44, R45, R42 and C35 showing as the symmetric matching circuit on the CH0_OUT trace.

    R63 and C44 provide a low pass filter on the OPA_OUT pin before the signal goes into the MCU.

    OPA838 is a pin-to-pin replacement for the OPA836. OPA838 has a better input voltage noise performance rather than the OPA836. OPA838 can provide enhanced standard deviation performance up to 2.5x lower than the OPA836 and is a drop-in replacement. For more information, refer to TIDM-02003.

  5. For the power supply U4, U5 and U6, TI recommends to use a dedicate LDO, DCDC power supply for the MCU. A good load transient response performance is important for ultrasonic applications. When users do not need the 5V feature, the U5 5V DCDC is not necessary in the board. Users can also use one LDO to provide both VCC_TX and VCC_RX to save BOM value. This needs to connect the TxPwr and RxPwr together on the hardware for the changing or change the configuration in the software to save one GPIO.
  6. For the USSXT, TI recommends to choose the load capacitor value by using Equation 11.
    Equation 11. C c r y s t a l + C l o a d + C l a y o u t = 34 p F

    Since the ADC approach is used in the USSLib, the measurement accuracy is barely affected by the crystal oscillator accuracy. Therefore, use a resonator on the EVM boards for demonstration with good performance. A resonator also consumes less current than a crystal. If users do not care about the current consumption and have a wide temperature range in the application, then users can consider to use a crystal to replace the resonator. Users need to modify the USS_HSPLL_INPUT_CLK_TYPE and USS_HSPLL_USSXTAL_SETTLING_USEC in the software.

  7. For the CHx_IN, OUT AFE circuit, TI recommends to use 1% resistors and 1% NP0 capacitors for a better measurement performance. For more details, refer to the EVM bill of materials list.
  8. For the USS GUI connection, TI recommends to keep the I2C connection port (COMM_SDA, COMM_SCL and COMM_IRQ) on the board at first. To debug issues with USS GUI at the evaluation stage is easy.
  9. For evaluating with MSP430FR5043, the default MSP430FR5043 linker file must be modified to meet the memory configuration required for the USS library. Use the lnk_msp430fr6043.cmd in the MSP430FR6043EVM_USS_Gas_Demo. Change the name to FR5043 and start evaluation. The MSP430FR5043 does not include LCD support, so the software must be modified to disable the LCD and any related functions. This is handled in hal_lcd.h.