AP3301

Document number: DS38018 Rev. 4 - 2

10 of 16

www.diodes.com

June 2016

© Diodes Incorporated

AP3301

Multi-Mode Operation

The switching frequency curve in Figure 1 shows three operation modes.



Burst Mode

At no load and light load, the system will operate at burst mode. In burst mode, the switching frequency is fixed at about 22kHz to avoid

audible noise. When the FB voltage is lower than 1.55V, the controller will not provide driving signal and the FB voltage will rise above

1.65V, then the driving signal will resume. By this control strategy, the system will eliminate a bunch of pulses and the power loss is

reduced.



QR Mode

AP3301 will count it as one valley. At light load and medium load, the system will enter QR mode. As the load changes, the trend of the

switching frequency in QR mode is modulated by AP3301 and following the internal arithmetic it is increased or decreased. In general when

the turning-on valley changes, the frequency will jump to a new value, this frequency jump transits quickly and the turning-on valley

changes between two neighboring valleys back and forth, this unstable condition introduces unacceptable audible noise. In benefit of

Diodes

proprietary “Valley Lock” technology, the turning on valley is locked and will not switch iteratively when the load is changed.

Meanwhile, the frequency dithering function is built in to reduce EMI emission. As Figure 2 shows, switching frequencies between the

power increase and power decrease line are a little different because of the inherent characteristic of valley-lock QR control, and it will

result in a tiny difference in efficiency. When the load increases, the switching frequency is also increased, a frequency of 120kHz is set to

clamp the maximum operating frequency, if this 120kHz is touched, the system will operate in normal DCM mode, and will return to QR if

the load continues to increase.



CCM Mode

With the load increases, if the switching frequency decreases below 62kHz in valley1 mode, CCM mode is implemented to achieve high

efficiency. Usually at low line voltage, the system will enter CCM mode at heavy load, while high line voltage the system may still operate at

QR mode with 1st or 2nd valley on.

Start-up Current and UVLO

The start-up current of AP3301 is optimized to realize ultra low current (1

direct benefit of low start-up current is the availability of using large start-up resistor, which minimizes the resistor power loss for high voltage AC

input.

An UVLO comparator is included in AP3301 to detect the voltage on VCC pin. It ensures that AP3301 can draw adequate energy from hold-up

capacitor during power-on. The turn-on threshold is 15.8V and the turn-off threshold is 7.6V.

Current Sense Comparator and PWM Latch

The AP3301 operates as a current mode controller, the output switch conduction is initiated by every oscillator cycle and is terminated when the

peak inductor current reaches the threshold level established by the FB pin. The inductor current signal is converted to a voltage signal by

S

FB

PK

R

V

I

3

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0

.

1

(

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short test. Few drive cycles can alleviate the destruction range and get better protection.

Leading-edge Blanking

edge blank is built-in to prevent the false-triggering caused by the turn-on spike. During this period, the current limit comparator is disabled and

the gate driver cannot be switched off.

At the time of turning off the MOSFET, a negative undershoot (maybe larger than -0.3V) can occur on the SENSE pin. So it is strongly

recommended to add a small RC filter or at least connect a resistor “R” on this pin to protect the IC (Shown as Figure 2).