AP65101

Document number: DS38098 Rev. 2 - 3

8 of 14

www.diodes.com

December 2016

© Diodes Incorporated

AP65101

NOT RECOMMENDED FOR NEW DESIGN

Application Information

Theory of Operation

The AP65101 is a 1.5A current mode control, synchronous buck regulator with built in power MOSFETs. Current mode control assures excellent

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

AP65101.

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. Since the current mode control is subject to sub-harmonic oscillations that start at half the switching frequency, ramp slope

compensation is utilized. This will help to stabilize the power supply. 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” from 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 AP65101 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 above this threshold.

Automated No-Load and Light-Load Operation

The AP65101 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 AP65101 automatically detects the peak inductor current and enters the light load

high-efficiency mode when the inductor peak current goes below 500mA. Once the inductor peak current exceeds this level, the AP65101

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