AP39303

Document number:DS41017 Rev. 7 - 3

12 of 16

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AP39303

Operation Description (continued)

S

If Fault Occurs

GATE

Vcc

I_CHG

VST

VCC-UVLO

3V

I CHARGE-L

I CHARGE - H

I CHARGE-FAULT

I CHARGE-H

0mA

0mA

Figure 5

Built-In VCC LDO

The AP39303 integrates a VCC LDO circuitry, the LDO regulates the wide range VCC_IN which is rectified from auxiliary winding to an acceptable

value. It makes the AP39303 a good choice in wide range output voltage application.

Brown In/Out Protection

To avoid potential high-current stress at low line voltage, the AP39303 introduces a reliable brownout protection. The AC line voltage is detected

through HV pin, a pair of high-voltage diodes are connected to the AC line which will rectify the AC input voltage to a double-frequency positive

voltage referring to GND, a 20k

Ω resistor is recommended to be added to improve the surge immunity. When the voltage across HV pin is higher

than VBR-IN for about 100µs of tBR-IN and VCC reaches VST, the system starts to work. If the HV pin voltage falls below VBR-OUT and lasts for 50ms

of tBR-OUT, the system will shut down until the line voltage rises over its brown-in voltage again.

SOVP/SUVP Protection

The AP39303 provides output OVP and UVP protection function. The auxiliary winding voltage during secondary rectifier conducting period

reflects the output voltage. A voltage divide network is connected to the auxiliary winding and DEM pin, the DEM pin will detect the equivalent

output voltage with a delay of tSAMPLE from the falling edge of GATE driver signal, as shown in Figure 6. The detected voltage will be compared to

the SOVP and SUVP threshold voltage VTH-SOVP and VTH-SUVP. If the SOVP or SUVP threshold is reached continuously by 7 switching cycles, the

SOVP or SUVP protection will be triggered, the AP39303 will shut down and the system will restart when the VCC voltage falls below the UVLO

voltage.

To prevent from false-trigger of SUVP during start up process, a blank time of tBLANK-SUVP is set during which the SUVP protection function is

ignored.

VAUX

VDEM

0V

Gate

tSAMPLE

Figure 6