FSL518APG datasheet(18/27 Pages) ONSEMI

18 / 27 page

FSL518H, FSL538H, FSL518A, FSL538A

www.onsemi.com

Figure 40. Timing Chart of OLP

IDRAIN

Protection

VCC

VCOMP

tAR

VOLP

VCC−STOP

ILIM

VCC−HVREG

tD−OLP

Over Voltage Protection (OVP)

A malfunction of voltage-feedback circuitry for output

regulation in power converter could result in excessive

energy delivered to output. In this condition, both output

voltage and VCC can be increased by unstable operation, and

OVP will be triggered after delay time tD−OVP when VCC

rises above VCC−OVP.

Figure 41. Timing Chart of OVP

tAR

VCC −STOP

VCC −HVREG

VCC−OVP

tD−OVP

Fault

Protection

Vcc

IDRAIN

Abnormal Over-Current Protection (AOCP)

When the secondary-side rectifier diodes or the

transformer windings are shorted, a steep drain current with

extremely high di/dt will flow through the MOSFET during

the minimum turn-on time. Under this condition, each

switching cycle generates very high current stress on power

MOSFET. The controller monitors drain current within a

limited leading-edge time duration tLEB + tAOCP of each

switching cycle. If drain current exceeds current limit for a

few consecutive switching cycles, NAOCP-TRIG, switching

will be stopped for number of pulses, NAOCP-HALT. If the

fault condition is met for three times, NAOCP-COUNT, the

controller goes into protection mode as shown in Fig. 42.

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