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AN1768

APPLICATION NOTE

®

ADMISSIBLE AVALANCHE POWER OF SCHOTTKY DIODES

October 2003 - Ed: 1

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.

0

0.2

0.4

0.6

0.8

1

1.2

25

50

75

100

125

150

175

Tj (°C)

P

(t , T ) / P

(tp, 25°C) versus T

ARM p

j

ARM

j

Fig. 2: Avalanche power derating over tempera-

ture range.

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

STMicroelectronics guarantees for each Schottky

diode a reference avalanche power given at

sponding to a rectangular current pulse ).

numbers.

Part number

per diode

STPS1545D (2x7.5A)

2.7 kW

STPS2045CT (2x10A)

4 kW

STPS3045CT (2x15A)

6 kW

STPS20H100CT (2x10A)

10.8 kW

Schottky diodes.

Derating curves

figure 2 and figure 3 give the ad-

missible avalanche power versus tp and Tj.

the derating curves are given in the respective

datasheet.

The designer must ensure that the guaranteed

P

(t , T ) / P

(1µs,

) versus tp

ARM p

j

ARM

tp(µs)

10

1

1

0.01

0.1

0.1

0.001

0.01

100

1000

10

Fig. 3: Avalanche power derating over pulse dura-

tion range