The average output current needs to be supplied by the piezo amplifier during continuous operation.
For short periods of time, a higher current can be required (e.g. maximum slope of sinusoidal signal).
This is approximated by multiplying the average output current by a correction factor which depends on the drive signal type (see graphics).
If the calculated peak current is not well below the specified peak current of the amplifier, the expected amplitude at a given frequency cannot be reached in continuous operation, even if the average output current is in spec (the target signal would be distorted, e.g. sinusoidal would appear triangular).
The higher the required peak current, the longer it takes for the amplifier to recover.