In this section, to verify the theory, we measure the voltage drop with different output current. We choose TPS629210 and LMR51610 to perform these tests. TPS629210 is the newest TI 3-17V, 1A synchronous buck converter with 100% duty cycle function. LMR51610 is TI newest wide range V_in, 1A synchronous buck converter with 98% maximum duty cycle.

An important factor influencing the measurement of the voltage drop in a buck converter is the deviation of the feedback resistor from the standard value. Deviation of the feedback resistor causes the output voltage to deviate from the calculated value. Therefore, we cannot consider the calculated output voltage to be the designed for value. To make sure that the buck converter operates in the dropout zone, making sure that the device has reached the maximum duty cycle.

The TPS629210 has 100% duty cycle function. First we choose a fixed output voltage and then the voltage drop can be measured by adjusting the input voltage when the duty cycle reaches 100%.

The LMR51610 designed for duty cycle is 98%. The cycle is limited by the minimum off time and maximum on time as shown in Equation 8 which is 200nS and 5uS respectively. However, in practice, the minimum off time can have some deviation. The practical duty cycle of LMR51610 is measured during in the following chapter.

Where:

• T_onmax is the maximum on time
• T_offmin is the minimum off time

Based on Equation 8 and the typical number in data sheet, the calculated duty cycle is 96%.