The ultrasonic mode is an unique control feature that keeps the switching frequency above the acoustic audible frequency toward no load condition. The ultrasonic mode control circuit monitors the switching frequency and keeps the switching frequency above 25 kHz to avoid the acoustic band. The output voltage becomes typically 1.6% higher than PWM operation. Figure 8-4 illustrates the details of ultrasonic mode operation.

Figure 8-4 Ultrasonic Mode Operation