AN869 Datasheet, PDF (2/4 Pages) STMicroelectronics – Tj MAX LIMIT OF SCHOTTKY DIODES

AN869 APPLICATION NOTE
The limit of the reverse current at V_R and Tj max before reaching thermal runaway is given by:
I_R(15V,Tjmax) = _V----_R----₍--₁----_–-----_δ---₎---_c1---_R----_t--_h---₍---_j---_–----_a----₎
Where c is a thermal coefficient c ≈ 0.055
Rth(j-a) = Rth(j-c) + Rth(c-a)
We have: I_R (15V, Tj max) = 242mA
Tj max is given by:
Tjmax=
125
+
-¹--
C
In
-_I--_R---_m^I--^R---_a⁽---^1x---⁵₍---₁^V---₅-^,--_V-^T---_,-^j--^m₁---₂-^a--₅--^x-_°--⁾-_C----₎-
Tj max = 127°C
Second example:
Application parameters:
(1-δ) = 0.5
V_R = 5V
Rth(c-a) = 18.5°C/W
Diode parameters (STPS10L25D):
I_R max (5V, 125°C) = 125mA
Rth(c-a=) = 1.6°C/W
We have I_R (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.
2/4