SNVS723G October 2011 – July 2018 LMZ10500
The LMZ10500 features a transition mode designed to extend the output regulation range to the minimum possible input voltage. As the input voltage decreases closer and closer to VOUT, the off-time of the PFET gets smaller and smaller and the duty cycle eventually needs to reach 100% to support the output voltage. The input voltage at which the duty cycle reaches 100% is the edge of regulation. When the LMZ10500 input voltage is lowered, such that the off-time of the PFET reduces to less than 35ns, the LMZ10500 doubles the switching period to extend the off-time for that VIN and maintain regulation. If VIN is lowered even more, the off-time of the PFET will reach the 35ns mark again. The LMZ10500 will then reduce the frequency again, achieving less than 100% duty cycle operation and maintaining regulation. As VIN is lowered even more, the LMZ10500 will continue to scale down the frequency, aiming to maintain at least 35ns off time. Eventually, as the input voltage decreases further, 100% duty cycle is reached. This behavior of extending the VIN regulation range is illustrated in Figure 12.