The duty cycle for a buck regulator is defined as the ratio of tON to T. The output voltage is set by multiplying the input voltage by duty cycle. The amount of ripple current is also calculated by using duty cycle. As can be seen, the amount of ripple is proportional to duty cycle, the length of the total cycle time, and the difference between VIN and VOUT. It is inversely proportional to the amount of inductance in the system. Ripple current is used to calculate how much ripple voltage will be seen at the output. Ripple voltage is calculated by multiplying the ripple current by the ESR of the output capacitor.