SLAA941 March 2020 TUSS4440 , TUSS4470
If the driver voltage is to be generated internally by the TUSS44x0, then the VDRV_HI_Z bit field must be set to 0h to enable VPWR to VDRV regulation. Ensure the equivalent voltage of VDRV_VOLTAGE_LEVEL bit field is less than or equal to the voltage at the VPWR pin. If VDRV_VOLTAGE_LEVEL is greater than the voltage at VPWR, the SPI Interface Status Bit will report an error that the VDRV power regulator has not reached the programmed voltage level. If VDRV is sourced externally, keep the VDRV_HI_Z bit field set to 1h to disable internal VPWR to VDRV regulation.
The default number of burst pulses at the BURST_PULSE bit field is set to 0h, which allows for continuous pulsing. TI recommends to change this value to a specific number to prevent additional unintentional pulses that may damage the transducer. For applications that prioritize short ranging, using a low number of burst pulses such as 1 to 4 is recommended. Some transducers have a maximum number of burst pulses rating, which is typically 16 to 20.
Choose an IO_MODE based on the MCU's capabilities or user preference. TUSS44x0 has multiple modes to excite the transducer through the OUTA and OUTB pins. For each of the modes, the desired frequency of burst is supplied through an external clock or GPIO output on the IOx pins. This enables the user to supply a highly precise clock or GPIO output calibrated to the center frequency of transducer to enable the highest sound pressure level generation. These modes can be selected by the IO_MODE bit field in the DEV_CTRL_3 register. When IO_MODE = 0h, there is a SPI dependency to start a time-of-flight cycle. All other IO_MODEs only use the IOx pins to start a time-of-flight cycle.
The TUSS4440 current limit control block set by the XFMR_DRV_ILIM bit field drives current efficiently into the primary side of the transformer to achieve the maximum swing (set by voltage on the center tap and turn ratio of the transformer) on the secondary side. By default, the current limit is set to lowest value of 50 mA, which may be suitable for short range applications. To increase the maximum detectable range, increasing the current limit to a nominal 300 mA may be required for transducers with a larger driver voltage requirement.