AP3128

Document number: DS43487 Rev. 3 - 2

9 of 12

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September 2021

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AP3128

Operation Description (continued)

SOVP Protection Function

For some applications, the system requires the output overvoltage protection function. The DEM pin will comapre the divided voltage from the VCC

winding with the inner threshold. When the voltage between RDEM and RSOVP is higher than VTH-SOVP during primary power MOSFET turning off

duration, the AP3128 will trigger SOVP function and the system will enter the latch protection mode. The Secondary Output Voltage Protection

(SOVP) can be achieved by this function since the value of the VCC winding

’s waveform reflects the output voltage precisely.

Other System Protection and Pin Fault Protection

The AP3128 provides versatile system and pin fault protections. The OCP comparator realizes the cycle-by-cycle current limiting (OCP). In universal

input line voltage, the IC realizes the constant over load protection (OLP). VCC overvoltage protection can be applied as the primary OVP or opto-

coupler broken protection. The AP3128 also has pin fault connection protection, including floating and short connection. The floating pin protection

includes the SENSE, FB, etc. The short pin protection includes the DEM pin short protection. When these pins are floated or the DEM pin is shorted

to ground, PWM switching will be disabled, thus protecting the power system.

Internal OTP Protection Function

The AP3128 integrates an internal temperature sensor. It has a trigger window of entering OTP mode at +150°C and exiting at +125°C. The internal

OTP protection mode is auto-recovery mode.