MAX6495(2005) Ver la hoja de datos (PDF) - Maxim Integrated

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MAX6495
(Rev.:2005)

72V, Overvoltage-Protection Switches/Limiter Controllers with an External MOSFET

Maxim Integrated 

72V, Overvoltage-Protection Switches/Limiter

Controllers with an External MOSFET

During ∆t2, COUT loses charge through the output load.

The voltage across COUT (∆V2) decreases until the

MOSFET reaches its VGS(TH) threshold and can be

approximated using the following formula:

∆V2

= IOUT

∆t2

COUT

Once the MOSFET VGS(TH) is obtained, the slope of the

output-voltage rise is determined by the MOSFET Qg

charge through the internal charge pump with respect

to the drain potential. The new rise time needed to

reach a new overvoltage event can be calculated using

the following formula:

∆t3

≅

QGD

VGS

∆VOUT

IGATE

where QGD is the gate-to-drain charge.

The total period of the overvoltage waveform can be

summed up as follows:

tOV = ∆t1 + ∆t2 + ∆t3

The MAX6495/MAX6496/MAX6499 dissipate the most

power during an overvoltage event when IOUT = 0. The

maximum power dissipation can be approximated

using the following equation:

PDISS

=

VOV ×

0.975 × IGATEPD ×

∆t1

∆tOV

The die-temperature increase is related to θJC (8.3°C/W

and 8.5°C/W for the MAX6495/MAX6496/MAX6499,

respectively) of the package when mounted correctly

with a strong thermal contact to the circuit board. The

MAX6495/MAX6496/MAX6499 thermal shutdown is

governed by the equation:

TJ = TA + PDISS x θJC < +170°C

12V IN

GATE

IN

OUTFB

MAX6495

SHDN

OVSET

GND

DC-DC

CONVERTER

IN

OUT

GND

Typical Application Circuits

DC-DC

CONVERTER

IN

OUT

GND

GATE

12V

IN

OUTFB

MAX6496

SHDN

GATEP

OVSET

GND

Figure 5. Overvoltage Limiter (MAX6495)

Figure 6. Overvoltage Limiter with Low-Voltage-Drop Reverse-

Protection Circuit (MAX6496)

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