During an initial overvoltage occurrence, the discharge

time (

discharge time is approximately:

current.

Upon OUT falling below the threshold point, the

MAX6495/MAX6496/MAX6499s’ charge-pump current

must recover and begins recharging the external GATE

the MOSFET’s gate threshold voltage is:

the internal clamp (from OUTFB to GATE) diode’s for-

current (100µA typ).

During

approximated using the following formula:

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:

The total period of the overvoltage waveform can be

summed up as follows:

The MAX6495/MAX6496/MAX6499 dissipate the most

maximum power dissipation can be approximated

using the following equation:

The die-temperature increase is related to

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:

Based on these calculations, the parameters of the

MOSFET, the overvoltage threshold, the output load

current, and the output capacitors are external vari-

ables affecting the junction temperature. If these para-

meters are fixed, the junction temperature can also be

affected by increasing

is on. By increasing the capacitance at the GATE pin,

required to charge up this additional capacitance

(75µA gate current). As a result,

PV

I

t

t

DISS

OV

GATEPD

OV

.

=×

×

×

0 975

1

∆

∆

∆

∆

t

Q

V

V

I

GD

GS

OUT

GATE

3

≅

∆

∆

VI

t

C

OUT

OUT

2

2

=

∆tC

VV

I

ISS

GS TH

D

GATE

2

()

=

+

∆tC

V

II

OUT

OV

OUT

GATEPD

1

095

.

(

)

=

×

+

72V, Overvoltage-Protection Switches/

Limiter Controllers with an External MOSFET

______________________________________________________________________________________

11

GATE

OUTFB

Figure 5. MAX6495/MAX6496/MAX6499 Timing