IRFS/SL4615PbF
www.irf.com 5
Fig 13. Maximum Effective Transient Thermal Impedance, Junction-to-Case
Fig 14. Typical Avalanche Current vs.Pulsewidth
Fig 15. Maximum Avalanche Energy vs. Temperature
Notes on Repetitive Avalanche Curves , Figures 14, 15:
(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 16a, 16b.
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 14, 15).
t
av =
Average time in avalanche.
D = Duty cycle in avalanche = t
av
·f
Z
thJC
(D, t
av
) = Transient thermal resistance, see Figures 13)
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
1E-006 1E-005 0.0001 0.001 0.01 0.1
t
1
, Rectangular Pulse Duration (sec)
0.001
0.01
0.1
1
10
T
h
e
r
m
a
l
R
e
s
p
o
n
s
e
(
Z
t
h
J
C
)
°
C
/
W
0.20
0.10
D = 0.50
0.02
0.01
0.05
SINGLE PULSE
( THERMAL RESPONSE )
Notes:
1. Duty Factor D = t1/t2
2. Peak Tj = P dm x Zthjc + Tc
1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01
tav (sec)
0.1
1
10
100
A
v
a
l
a
n
c
h
e
C
u
r
r
e
n
t
(
A
)
0.05
Duty Cycle = Single Pulse
0.10
Allowed avalanche Current vs avalanche
pulsewidth, tav, assuming ∆Τ j = 25°C and
Tstart = 150°C.
0.01
Allowed avalanche Current vs avalanche
pulsewidth, tav, assuming ∆Tj = 150°C and
Tstart =25°C (Single Pulse)
25 50 75 100 125 150 175
Starting T
J
, Junction Temperature (°C)
0
20
40
60
80
100
120
E
A
R
,
A
v
a
l
a
n
c
h
e
E
n
e
r
g
y
(
m
J
)
TOP Single Pulse
BOTTOM 1.0% Duty Cycle
I
D
= 21A
τ
J
τ
J
τ
1
τ
1
τ
2
τ
2
τ
3
τ
3
R
1
R
1
R
2
R
2
R
3
R
3
Ci= τi/Ri
τ
C
τ
4
τ
4
R
4
R
4
Ri (°C/W) τi (sec)
0.02324 0.000008
0.26212 0.000106
0.50102 0.001115
0.25880 0.005407
