There are two control schemes for these devices- Pulse Width Modulation (PWM) and Pulse Frequency Modulation (PFM). Looking at the graph on the left, the XC9235 has PWM fixed control with its efficiency curves shown by the dashed lines. The frequency is always fixed at either 3MHz or 1.2MHz providing the advantage of an output voltage ripple that is small. The XC9236 has PFM/PWM auto switching control. Their efficiency curves are shown by the continuous lines. The advantage for PFM/PWM auto switching is that efficiencies are high at light loads. The graph on the left shows the efficiency stays greater than 80% even if the load current goes down to 1mA. In the PFM mode, the frequency goes down to 27kHz as shown in the upper-right hand graph. One point which should be noted is that efficiency is influenced by the frequency of the product selected. The 1.2MHz version has a higher efficiency than the 3MHz version.