IR3640MPBF datasheet(13/32 Pages) IRF

13 / 32 page

06/15/2009

IR3640MPBF

Power Good and Over-voltage Protection

The IC continually monitors the output voltage via

sense pin. The Vsns voltage compares to a fixed

voltage. As soon as the sensed voltage reaches

0.88*Vref, the Power Good signal flags. Power

Good pin needs to be externally pulled high. High

state indicates that output is in regulation. Figure

10a and 10b shows the timing diagrams of Power

Good function.

If the output voltage exceeds the over voltage

threshold, an over voltage trip signal asserts, this

will result to turn off the high side driver and turn

on the low side driver until the Vsns voltage

drops below 1.15*Vref threshold. Both drivers are

latched off until a reset performed by cycling

either Vcc or Enable.

The

OVP

threshold

can

externally

programmed to user defined value. Figure 10c

shows the response in over-voltage condition.

Fig.10a: IR3640 Non-Sequencing

Power Up (Seq=Vcc)

Fig.10b: IR3640 Sequencing

Power Up

Fig.10c: IR3640 Timing Diagram of Over-

voltage Protection

Thermal Shutdown

Temperature sensing is provided inside IR3640.

The trip threshold is typically set to 140oC. When

trip threshold is exceeded, thermal shutdown

turns off both MOSFETs and discharges the soft

start capacitor. Automatic restart is initiated when

the sensed temperature drops within the

operating range. There is a 20oC hysteresis in

the thermal shutdown threshold

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