English
Language : 

AN1768 Datasheet, PDF (1/2 Pages) STMicroelectronics – ADMISSIBLE AVALANCHE POWER OF SCHOTTKY DIODES
AN1768
®
APPLICATION NOTE
ADMISSIBLE AVALANCHE POWER OF SCHOTTKY DIODES
D. JOUVE
INTRODUCTION
The design of Switch Mode Power Supply (SMPS) is subjected to ever increasing cost and efficiency
constraints.
One way to respond to these aggressive specifications is to use components closer to their intrinsic limits.
The increasing use of Schottky diodes in the avalanche area is a good example of this evolution.
To help the designer to optimize the choice of the Schottky diode in a rectification application,
STMicroelectronics is proposing a simple tool to determine if a given ST Schottky diode can withstand the
avalanche energy fixed by the application conditions.
1. DESIGN RULES
The first step for the designer is to estimate, in the
worst-case conditions, the following parameters:
n Operating junction temperature: Tj
n Pulse duration of the avalanche current: tp
n Avalanche energy by pulse generated by the
converter in the Schottky diode: EAP
STMicroelectronics guarantees for each Schottky
diode a reference avalanche power given at
tp=1µs and Tj=25°C: PARM(1µs,25°C) (corre-
sponding to a rectangular current pulse ).
Table 1 gives PARM(1µs,25°C) for some part
numbers.
Table 1: PARM(1µs, 25°C) values for some ST
Schottky diodes.
Part number
PARM(1µs; 25°C)
per diode
STPS1545D (2x7.5A)
2.7 kW
STPS2045CT (2x10A)
4 kW
STPS3045CT (2x15A)
6 kW
STPS20H100CT (2x10A)
10.8 kW
Derating curves figure 2 and figure 3 give the ad-
missible avalanche power versus tp and Tj.
PARM(1µs, 25°C) for each part number as well as
the derating curves are given in the respective
datasheet.
The designer must ensure that the guaranteed
avalanche energy EARM(tp,Tj) is greater than the
avalanche energy in the application EAP.
October 2003 - Ed: 1
Fig. 2: Avalanche power derating over tempera-
ture range.
PARM(tp, Tj) / PARM(tp, 25°C) versus Tj
1.2
1
0.8
0.6
0.4
0.2
0
Tj (°C)
25
50
75
100
125
150
175
Fig. 3: Avalanche power derating over pulse dura-
tion range
PARM(tp, Tj) / PARM(1µs, Tj) versus tp
10
tp(µs)
1
0.01
0.1
1
0.1
10
100
1000
0.01
0.001
1/2
 ▷