IC returns MXPWR warnings

When operating the BOS1921 and playing waveforms, I receive many MXPWR warnings, either in Haptic Studio or using the SDK. What should I do?

The Boreas driver provides error flagging to help the integrator identifying problems in the design. Note that MXPWR is not an error but only a warning. It will not prevent a waveform from playing but it is an indication that the driver has reached the maximum amount of power it can transfer and that the waveform may be distorted.

A distorted waveform may produce undesirable audible noise and loss of haptic performance. Although operating the IC with MXPWR warning does not pose a risk for the hardware, if a prototype is showing significant MXPWR warnings and the situation is not corrected, inconsistencies may appear in production where tolerances come into play.

Some solutions to reduce MXPWR occurrence are:

• adjust register parameters : many parameters may be adjusted to optimize the waveform shape and power consumption, which may also affect MXPWR occurrences. Please consult chapter 9 - IC performance optimization - of our Solid-State Button Design – Hands-on Guide application note.

• change BOM to allow more output power if possible : reduce Rsense and change the inductor accordingly.

• change waveforms : steep transitions and high-frequency content will need higher power transfer rates leading to MXPWR conditions, especially when rising the voltage on the output. Use lower frequency waveforms, lower amplitudes. An interesting solution could be to lower the frequency on the voltage rise part of the waveform (reducing the power intake) while keeping or increasing the voltage fall part of the waveform (keeping good haptic in that region).

• change operating conditions : output drive is also a function of the piezo actuator capacitance and the supply level. Reducing the piezo actuator capacitance, if possible while meeting other application constraints, would reduce the needed power. Using a higher supply level will yield higher output drive – if the system uses both 3.3 and 5V rails, supplying VBUS from the 5V might be preferable.

• if more power is needed, consider enabling the CCM mode or using another driver IC with more power output.