Electronic Design

Constant On-Time Buck Regulator ICs

How did the constant ontime (COT) buck regulator IC evolve?

The COT regulator is a modified version of the basic hysteretic regulator shown in Figure 1. The basic hysteretic regulator IC consists of a comparator with input hysteresis that compares the output feedback voltage with a reference volt turning off the buck switch MOSFET.

When the feedback voltage exceeds the reference voltage, the comparator output goes low, turning off the buck switch MOSFET. The switch remains off until the feedback voltage falls below the reference hysteresis voltage. Then, the comparator output goes high, turning on the switch and allowing the output voltage to rise again.

What are the characteristics of the basic hysteretic buck regulator IC?

It reacts extremely quickly to load and line transients due to itswide bandwidth control loop. Unlike a pulsewidth modulation (PWM) regulator, this loop does not require an error amplifier or frequency compensation.

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