CCS/PGA460-Q1: PGA460-Q1 :How do I successfully use a high-frequency transducer (180-480kHz)

user1327352,

Yes, you can use a 300 kHz mono-static or bi-static transducer configuration with the direct driven circuit.

The process is no different that that of the lower frequency transducers (30-80 kHz).

For guidance on using a different transducer on the EVM's Direct Driven daughtercard, refer to FAQ # 4.4.2 "How do I use a different transducer on the direct driven circuit?" from the PGA460 FAQ at http://www.ti.com/lit/an/slaa733/slaa733.pdf.

The only additional consideration for high frequency transducers (180-480kHz) is in software because the DSP coefficients are not automatically updated when the FREQUENCY register is written to. The additional step of updating the DSP coefficients in a high frequency case is explained in FAQ # 5.10 "How do I successfully use a high-frequency transducer (180-480kHz) with the GUI?" . The GUI now automatically updates the DSP coefficients, but if you are implementing a custom software solution, you will need to replicate the DSP coefficient write procedure described. This additional requirement is also described in section 7.3.4.1 Ultrasonic Echo—Band-Pass Filter of the datasheet:

The band-pass filter is a second-order Butterworth IIR type filter. On power up, the PGA460-Q1 device calculates
the coefficients and places them in the BPF_A2_xSB, BPF_A3_xSB, and BPF_B1_xSB registers. These
registers can be overwritten by the user to reconfigure the filter. However, if the FREQ or BPF_BW bit is
changed, the coefficient calculation sequence is rerun and the device rewrites these registers. In case the
FREQ_SHIFT bit is set to 1 (80- to 480-kHz driving frequency range), the band-pass filter coefficients are not
calculated automatically by the PGA460-Q1 device. In this case the MCU is required to write these values
through the UART or USART interface.

A DSP band-pass coefficient look up table is included in the PGA460-Q1 EVM GUI, is dependent on the frequency and band-pass filter bandwidth.

Hi user1327352,

Responding to your questions:

1) Based on your first image, you are powering the PGA460 with the USB step-up circuit to generate a VPWR_DD voltage of 7V. In the half-bridge driver configuration, this means you are only exciting the transducer with 7Vpp total, whereas a transformer driver would generate 140Vpp. It is difficult to determine if the transducer you are using if closed-top or not, but you may need a larger VPWR_DD voltage to properly excite the transducer. The maximum driver voltage I recommend you try using is 28V. You can also power the device from a 28V supply to simplify the EVM setup. Remember to completely remove the jumper on the BOOSTXL-PGA460 board when using an external supply on the EVM's MAIN supply net. What is the transducer part number and/or voltage driver specification of the transducer?

2) You setup for the high-frequency mode is correct, and the driving signal appears to be correct also. You may not see anything on the return envelope due to the weak driving voltage, or you may need to increase the digital gain setting. According to your echo data dump capture, your digital gain is x2 on preset 1 and x1 on preset 2. Try increasing these values to x8, x16, or x32.

3) High frequency transducers (i.e. 300kHz) typically have a very short maximum range (typically <1m). Your time access is currently configured for 16ms (2.8m). I recommend, that you reduce the record time for your initial debug/evaluation to the minimum of 4.096ms (70cm). This will allow you to see objects very close, even if they are weak, to confirm the presence of any echo activity when using a 7V half bridge driver.