AP3118 datasheet(13/17 Pages) DIODES

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AP3118

Document number: DS39915 Rev. 5 - 2

13 of 17

www.diodes.com

July 2018

AP3118

Operation Principle Description (Cont.)

Built-In Slope Compensation

It is well known that a continuous current mode SMPS may become unstable when the duty cycle exceeds 50%. The built-in slope compensation

in the AP3118 can keep the system stable.

Built-In VCC LDO

The AP3118 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 AP3118 a good choice in wide range output voltage application.

Brown In/Out Protection

To avoid potential high-current stress at low line voltage, the AP3118 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 GATE pin will output drive signals and the system starts to work. If the HV pin

voltage falls below VBR-OUT and lasts for 50ms of tBR-OUT, the GATE pin will turn off and the system will shut down until the line voltage rises over

its brown-in voltage again.

SOVP/SUVP Protection

The AP3118 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 8. 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 AP3118 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.

Two levels of OCP Control

The AP3118 sets two levels OCP protection thresholds to distinguish overload protection and short circuit protection. When overload condition

occurs (

), the internal timer begins to operate. After 120ms, IC enters into protection status. For short circuit protection

(FB>4.2V), the internal timer is set to 30ms.

Externally Triggered Protection

The AP3118 reserves flexible protection mode for power design. The CTRL Pin can achieve external programmable protection. A high threshold

of VTH-CTRL-H is set for any over voltage protection, if the CTRL Pin voltage is higher than the threshold for 7 switching cycles, the CTRL-High

protection will be triggered. A low threshold of VTH-CTRL-L is usually used for external over temperature protection. To realize the external OTP, a

proper value NTC should be connected from the CTRL Pin to the ground. An inner current of 100µA flows through the NTC from the CTRL pin. If

the CTRL Pin voltage is lower than the VTH-CTRL-L for 32ms duration at least, the CTRL-Low protection will be triggered. Whenever the

protection is triggered, the system will stop the output drive signal and will restart after the VCC voltage falling below the UVLO voltage.

System Protection

LOVP, FOCP, SSCP, VCC OVP, OTP

The AP3118 provides versatile protection to ensure the reliability of the power system. LOVP achieves line voltage overvoltage protection, if the

detected AC line voltage is higher than VLOVP for 7 switching cycles, the LOVP protection will be triggered. FOCP protection is an ultra-fast short-

current protection which is helpful to avoid catastrophic damage of the system when the secondary rectifier is short. The primary peak current will

be monitored by SENSE pin through a primary sense resistor, whenever the sampled voltage reaches the threshold of VTH-FOCP for 7 switching

cycles continuously, the FOCP protection will be active to shut down the switching pulse. SSCP might be triggered at ultra-low line voltage

condition or other failure condition that short the SENSE pin to ground. The SSCP module senses the voltage across the primary sense resistor

with a delay of 4µs after the rising edge of primary GATE signal, this sensed signal is compared with VTH-SSCP. If it is lower than VTH-SSCP for 7

switching cycles, the SSCP protection will be triggered and the drive signal will be disabled. All these protections described above will restart the

system when the VCC voltage falls below UVLO. Although the external OTP can be easily implemented through CTRL pin, the AP3118 still

reserves the inner OTP with a hysteresis for any necessary use.

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