AP65111

Document number: DS39153 Rev. 3 - 3

8 of 14

www.diodes.com

January 2018

© Diodes Incorporated

AP65111

Application Information

Theory of Operation

The AP65111 is a 1.5A current mode control, synchronous buck regulator with integrated power MOSFETs. Current mode control assures

excellent line regulation, load regulation, and a wide loop bandwidth for fast response to load transients. Figure 1 depicts the functional block

diagram of AP65111.

The operation of one switching cycle can be explained as follows: The rising edge of the 500kHz oscillator clock signal sets the RS Flip-Flop. Its

output turns on HS MOSFET. When the HS MOSFET is on, inductor current starts to increase. The current sense amplifier senses and amplifies

the inductor current with a gain of 0.22V/A. Since the current mode control is subject to sub-harmonic oscillations that start at half of the

switching frequency, ramp slope compensation of 0.9V/T is utilized. This ramp compensation is summed to the current sense amplifier output

and compared to the error amplifier output by the PWM comparator. When the sum of the current sense amplifier output and the slope

compensation signal exceeds the EA output voltage, the RS Flip-Flop is reset and HS MOSFET is turned off.

When the HS MOSFET turns off, the synchronous LS MOSFET turns on until the next clock cycle begins. There is a “dead time” between the HS

turn off and LS turn on that prevents the switches from “shooting through” across the input supply to ground.

For one whole cycle, if the sum of the current sense amplifier output and the slope compensation signal does not exceed the EA output, then the

falling edge of the oscillator clock resets the Flip-Flop, and forces the MOSFET to turn off.

The voltage loop is compensated internally.

Enable

The enable (EN) input allows the user to control turning on or off the regulator. The AP65111 has an internal pull-down resistor on the EN pin

and when the EN is not actively pulled up the part turns off.

Quiescent Current

Above the ‘EN Rising Threshold’, the internal regulator is turned on and the quiescent current can be measured when VFB>0.8V.

Automated No-Load and Light-Load Operation

The AP65111 operates in light load high efficiency mode during low load current operation. The advantage of this light load efficiency mode is

lower power losses at no-load and light-load conditions. The AP65111 automatically detects the

inductor’s valley current and enters the light load

high-efficiency mode when value falls below zero Ampere. Once the inductor

’s valley current exceeds this zero Ampere, the AP65111 transitions

from light-load high-efficiency mode to continuous PWM mode.