AN869 Datasheet, PDF (1/4 Pages) STMicroelectronics – Tj MAX LIMIT OF SCHOTTKY DIODES

AN869
APPLICATION NOTE
Tj MAX LIMIT OF SCHOTTKY DIODES
INTRODUCTION
This application note is about the limit of Tj max given in the datasheet of SCHOTTKY rectifiers.
It explains the real meaning of this parameter and why in some applications, the component can operate
with a junction temperature higher than Tj max.
Table 1 shows the Tj max specified in the datasheet for the different families of SCHOTTKY diodes.
Table 1. Tj max versus SCHOTTKY family
SCHOTTKY FAMILY
STPSxxL10
STPSxxL25
STPSxx45
STPSxx100
V_RRM
(V)
10
25
45
100
Tj Max
(°C)
100
125
150
125
For a classical ultra fast rectifier, this limit is equal to 150°C. For a SCHOTTKY diode this limit is lower (for
instance 125°C for a STPSxxL25). This lower limit of Tj max is only due to thermal runaway phenomenon
linked to the leakage current. This phenomenon is explained in the application note: "THERMAL RUN-
AWAY IN RECTIFIER".
This application note describes the rules for the calculation of the limit before thermal instability is reached.
This limit depends on the characteristics of the diodes (leakage current: IR, junction to case thermal resis-
tance Rth(j-c) ...) and application parameters (reapplied voltage across the diodes: V_R, duty cycle of the
blocking of the diode: (1 - δ), thermal resistance of the heatsink: Rth(c-a) ...).
The following two examples show that for the same diode (STPS10L25D) different conditions lead to dif-
ferent limits for Tj max.
First example:
Application parameters:
(1-δ) = 0.5
V_R = 15V
Rth(c-a) = 8.5°C/W
Diode parameters: (STPS10L25D):
I_R max (15V, 125°C) = 210mA
Rth(j-c)=1.6°C/W
May 2004
REV. 2
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