AP3302 datasheet(11/17 Pages) DIODES

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AP3302

Document number:DS38882 Rev. 4 - 2

11 of 17

www.diodes.com

March 2017

AP3302

Operation Description (Cont.)

Start-Up Current and UVLO

The start-up current of the AP3302 is optimized to realize ultra low current (1

A typical) so that V

CC capacitor can be charged more quickly. The

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 AP3302 to detect the voltage on VCC pin. It ensures that AP3302 can draw adequate energy from VCC

capacitor during power-on.

VCC Maintain Mode

During some transient load condition, VFB will drop below 1.55V, thus the PWM drive signal will be stopped, and there is no more energy

transferring to the output side and auxiliary winding VCC supply. Therefore, the IC VCC voltage may reduce to the UVLO threshold voltage which

will results in unexpected system restart. To avoid this failure condition, the AP3302 has a so-called VCC maintain mode to maintain VCC voltage

above UVLO. Whenever VCC decreases to a setting threshold as VM, the VCC maintain mode will be awaked and AP3302 will output a driving

pulse to turn on primary switch for providing enough energy to VCC capacitor.

Leading-Edge Blanking Time

A narrow spike on the leading edge of the current waveform can usually be observed when the power MOSFET is turning on. A 250ns leading-

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

comparator are 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 4).

SENSE

GATE

Large undershoot (more than

-0.3V) may damage the SENSE pin

Necessary

Figure 4

Protections

Brown In and Brown Out

The AP3302 can easily achieve brown in and brown out protection with the help of an external setting resistor. To determine the brown in voltage,

according to the formula:

mainly determines the brown in voltage, it’s the upper resistor connected to the DEM Pin as shown in figure 5. Vindc is the peak value of

targeted brown-in AC voltage, Np is the primary winding turns and the Naux is the auxiliary winding turns. When the system is plugged in, the

AP3302 will output 4 switching pulses to identify the AC voltage value, when the primary MOSFET turns on, the DEM Pin is clamped to GND and

a current

will flow out of the DEM pin, passing through

and the auxiliary winding. The smaller

, the larger

. If the IC controller

detects that

is larger than

for the continuous 4 cycles, the IC will start outputting driving signal normally. Otherwise, whenever the

lower than

for a period of tDELAY-BNO, it will trigger the brown out protection and the IC will stop outputting driving signal.

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