IRFR/U540Z
100
Duty Cycle = Single Pulse
Avalanche Current (A)
10
0.01
0.05
0.10
Allowed avalanche Current vs
avalanche pulsewidth, tav
assuming
∆Tj
= 25°C due to
avalanche losses
1
0.1
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
tav (sec)
Fig 15.
Typical Avalanche Current vs.Pulsewidth
40
EAR , Avalanche Energy (mJ)
30
TOP
Single Pulse
BOTTOM 1% Duty Cycle
ID = 21A
20
10
0
25
50
75
100
125
150
Starting TJ , Junction Temperature (°C)
Notes on Repetitive Avalanche Curves , Figures 15, 16:
(For further info, see AN-1005 at www.irf.com)
1. Avalanche failures assumption:
Purely a thermal phenomenon and failure occurs at a
temperature far in excess of T
jmax
. This is validated for
every part type.
2. Safe operation in Avalanche is allowed as long asT
jmax
is
not exceeded.
3. Equation below based on circuit and waveforms shown in
Figures 12a, 12b.
4. P
D (ave)
= Average power dissipation per single
avalanche pulse.
5. BV = Rated breakdown voltage (1.3 factor accounts for
voltage increase during avalanche).
6. I
av
= Allowable avalanche current.
7.
∆T
=
Allowable rise in junction temperature, not to exceed
T
jmax
(assumed as 25°C in Figure 15, 16).
t
av =
Average time in avalanche.
175
D = Duty cycle in avalanche = t
av
·f
Z
thJC
(D, t
av
) = Transient thermal resistance, see figure 11)
P
D (ave)
= 1/2 ( 1.3·BV·I
av
) =
DT/
Z
thJC
I
av
= 2DT/ [1.3·BV·Z
th
]
E
AS (AR)
= P
D (ave)
·t
av
Fig 16.
Maximum Avalanche Energy
vs. Temperature
7 / 11
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