Depending on the quality of the source signal provided to the DRV2700 device, an input filter may be required. Some key factors to consider are whether the source is generated from a DAC or from PWM, and the out-of-band content generated. If proper anti-image rejection filtering is used to eliminate image components, the filter can possibly be eliminated depending on the magnitude of the out-of-band components. If PWM is used, at least a first-order RC filter is required. The PWM sample rate must be greater than 30 kHz to keep the PWM ripple from reaching the piezo element and dissipating unnecessary power. A second-order RC filter may be desirable to further eliminate out-of-band signal content to further drive down power dissipation and eliminate audible noise.

For this design example, to ensure higher harmonics of the input signal do not propagate into the device, use a low pass filter with a 3-dB point of 2 kHz. Refer to DRV2700EVM High Voltage Piezo Driver Evaluation Kit, SLOU403, to build this input filter network.