AN869 datasheet(2/4 Pages) STMICROELECTRONICS

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AN869 APPLICATION NOTE

2/4

The limit of the reverse current at VR and Tj max before reaching thermal runaway is given by:

Where c is a thermal coefficient c

≈ 0.055

Rth(j-a) = Rth(j-c) + Rth(c-a)

We have: IR (15V, Tj max) = 242mA

Tj max is given by:

Tj max = 127°C

Second example:

Application parameters:

(1-

δ) = 0.5

VR = 5V

Rth(c-a) = 18.5°C/W

Diode parameters (STPS10L25D):

IR max (5V, 125°C) = 125mA

Rth(c-a=) = 1.6°C/W

We have IR (5V, Tj max) = 363mA

and

Tj max = 144°C

CONCLUSIONS

This application note shows that the maximum limit of Tj of the SCHOTTKY diodes given in the datasheet

is mainly due to the thermal runaway phenomenon. This limit doesn’t only depend on diode parameters

but also application parameters. In the first example corresponding to a typical application we will find Tj

max given in the datasheet. The second example shows that in some applications SCHOTTKY diodes can

be used with a junction temperature higher than the Tj max given in the datasheet.

IR 15VTjmax

()

VR 1 δ

–

()cRth j a

–

()

----------------------------------------------------

Tjmax

125

----

IR 15VTjmax

()

IRmax 15V 125°C

()

--------------------------------------------------

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