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AN1768 Datasheet(PDF) 1 Page - STMicroelectronics |
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AN1768 Datasheet(HTML) 1 Page - STMicroelectronics |
1 / 2 page 1/2 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 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. 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 Table 1: PARM(1µs, 25°C) values for some ST Schottky diodes. 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. P (t , T ) / P (1µs, ) versus tp ARM p j ARM Tj 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 |
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