EVM430-FR6047: EVM430-FR6047

Hi Laurent,

1. The MSP430FR6047 device is capable of supporting transducer excitation frequencies down to about 130 kHz when setting the PLL frequency to 68 MHz. As discussed in Section 21.2.6 of the Device Family User's Guide (www.ti.com/.../slau367), the frequency is set by the PLL clock frequency and the SAPHPGLPER.LPER and SAPHPGHPER.HPER registers. Excitation pulse frequency = HSPLL frequency / ( SAPHPGHPER.HPER + SAPHPGLPER.LPER). The limitation is given by 68 MHz / (255+255) which is approximately 133.33 kHz.

2. The Ultrasonic Design Center is targeted initially for water flow meter customers who mostly use transducers that are in the range of 800 kHz to 2.25 MHz. That is the reason for the limitation of the 772 MHz as documented in the Design Center User's Guide. You can access it from the "Help" in the Design Center.

3. The MSP430FR6047 also has on on-chip PGA which can provide a gain of as much as 30.8 dB as discussed in Section 22.2.5 "PGA Gain Control" of the Device Family User's Guide (www.ti.com/.../slau367). This might allow you to operate with 1 MHz transducers all the way to 1.4 m.

4. If your system requires the use of transducers below the 175 kHz excitation frequency, small modifications will be needed to the application code file USS_userConfig.h in the Application example project where you can specify the transducer excitation frequency. You can set the USS_F1_FREQ to 175000 for 175 kHz. You will also need to disable the update for this frequency from the Design Center GUI in hmi.c:HMI_update_USSmeterConfig to ensure the "transFreq" is set to 175 kHz.
4b. If you use this approach, you also have to make sure the ADC sampling frequency is between 4x-8x of the transducer frequency. As an example, for 175 kHz, you have to restrict the ADC sampling frequency to between 700 kHz and 1400 kHz. The default ADC sampling frequency setting is 3.6 MHz for 1 MHz transducers.

Srinivas