7.4 Device Functional Modes

Figure 10 shows how duty cycle effects the operational mode and is useful for reference in the following discussions. Initially, only the buck switch is active and the buck duty cycle increases to maintain output regulation as VIN decreases. When VIN is approximately equal to 15.5 V, the boost switch begins to operate with a low duty cycle. If VIN continues to fall, the boost switch duty cycle increases and the buck switch duty cycle decreases until they become equal at VIN = 13.2 V.