MP155 – ENERGY EFFICIENT OFF-LINE REGULATOR

MP155 Rev. 1.12

www.MonolithicPower.com

11

10/28/2013

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Over Load Protection (OLP)

As the load increases, the peak current and the

switching frequency increase with the load. When

the switching frequency and peak current

reaches their maximums, the output voltage will

decrease if the load continues to increase. Then

the FB voltage will drop below OLP threshold.

By continuously monitoring the FB voltage, the

timer starts when the FB voltage drops below the

1.7V error flag threshold. Removing the error flag

resets the timer. If the timer continues to

This timer duration avoids triggering OLP when

the power supply starts up or enters a load

transition phase, and therefore requires that the

power supply start up in less than 170ms. A

over-load protection delay time, as shown below:

τ≈

×

Dealy

37kHz

170ms

fs

Short Circuit Protection (SCP)

The MP155 shuts down when the peak current

rises above 450mA as its short-circuit protection

threshold. The power supply resumes operation

after removing the fault.

Thermal shutdown (TSD)

To prevent from any lethal thermal damage, the

MP150 shuts down switching when the inner

shutdown (TSD), the VCC drops to 2.4V, and

then the internal high voltage regulator recharges

VCC.

Open Loop Detection

working and begins a re-start cycle. The open-

loop detection is blanked for 128 switching cycles

during start-up.

Leading-Edge Blanking

An internal leading-edge blanking (LEB) unit

between the current sense resistor inside the IC

and

the

current

comparator

input

avoids

prematurely switching pulse termination due to

the parasitic capacitance. During the blanking

period, the current comparator is disabled and

cannot turn off the external MOSFET. Figure 6

shows leading-edge blanking.

Figure 6: Leading-Edge Blanking