AUIRFR/U4104
1000
Duty Cycle = Single Pulse
Allowed avalanche Current vs
avalanche pulsewidth, tav
100
∆
assuming
Tj = 25°C due to
0.01
avalanche losses. Note: In no
case should Tj be allowed to
exceed Tjmax
0.05
10
0.10
1
0.1
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
tav (sec)
Fig 15. Typical Avalanche Current Vs.Pulsewidth
160
Notes on Repetitive Avalanche Curves , Figures 15, 16:
(For further info, see AN-1005 at www.irf.com)
1. Avalanche failures assumption:
TOP
BOTTOM 1% Duty Cycle
= 42A
Single Pulse
I
Purely a thermal phenomenon and failure occurs at a
D
120
80
40
0
temperature far in excess of Tjmax. This is validated for
every part type.
2. Safe operation in Avalanche is allowed as long asTjmax is
not exceeded.
3. Equation below based on circuit and waveforms shown in
Figures 12a, 12b.
4. PD (ave) = Average power dissipation per single
avalanche pulse.
5. BV = Rated breakdown voltage (1.3 factor accounts for
voltage increase during avalanche).
6. Iav = Allowable avalanche current.
7. ∆T = Allowable rise in junction temperature, not to exceed
Tjmax (assumed as 25°C in Figure 15, 16).
tav = Average time in avalanche.
25
50
75
100
125
150
175
D = Duty cycle in avalanche = tav ·f
Starting T , Junction Temperature (°C)
ZthJC(D, tav) = Transient thermal resistance, see figure 11)
J
PD (ave) = 1/2 ( 1.3·BV·Iav) = DT/ ZthJC
Iav = 2DT/ [1.3·BV·Zth]
EAS (AR) = PD (ave)·tav
Fig 16. Maximum Avalanche Energy
Vs. Temperature
8
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