5 2017-03-28
AUIRFS4127
Fig 13. Maximum Effective Transient Thermal Impedance, Junction-to-Case
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
22a, 22b.
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 = tav ·f
Z
thJC
(D, t
av
) = Transient thermal resistance, see Figures 14)
PD (ave) = 1/2 ( 1.3·BV·I
av
) = T/ Z
thJC
I
av
= 2T/ [1.3·BV·Z
th
]
E
AS (AR)
= P
D (ave)·
t
av
Fig 14. Avalanche Current vs. Pulse Width
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
T
h
e
r
m
a
l
R
e
s
p
o
n
s
e
(
Z
t
h
J
C
)
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
25 50 75 100 125 150 175
Starting T
J
, Junction Temperature (°C)
0
50
100
150
200
250
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% Duty Cycle
I
D
= 44A
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 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)
