GENERAL DATA — 1-3 WATT DO-41 SURMETIC 30
30
20
D =0.5
0.2
10
7
5
0.1
3
2
t
P
1
PK
0.05
t
2
DUTY CYCLE, D =t /t
0.02
0.01
1 2
1
0.7
0.5
NOTE: BELOW 0.1 SECOND, THERMAL
RESPONSE CURVE IS APPLICABLE
TO ANY LEAD LENGTH (L).
SINGLE PULSE
∆
T
=
∆
θ
T
(t)P
JL
JL
JL
PK
REPETITIVE PULSES
=
θ
(t,D)P
D = 0
JL
PK
0.3
0.0001 0.0002
0.0005
0.001
0.002
0.005
0.01
0.02
0.05
0.1
0.2
0.5
1
2
5
10
t, TIME (SECONDS)
Figure 2. Typical Thermal Response L, Lead Length = 3/8 Inch
3
1K
2
RECTANGULAR
NONREPETITIVE
1
0.5
500
T = 125°C
A
WAVEFORM
300
200
T
= 25°C PRIOR
J
0.2
0.1
TO INITIAL PULSE
0.05
100
0.02
0.01
0.005
50
30
20
T
= 125°C
0.002
0.001
A
0.0005
0.0003
10
1
2
5
10
20
50
100 200
400
1000
0.1
0.2 0.3 0.5
1
2
3
5
10
20 30 50 100
NOMINAL V (VOLTS)
Z
PW, PULSE WIDTH (ms)
Figure 3. Maximum Surge Power
Figure 4. Typical Reverse Leakage
APPLICATION NOTE
Since the actual voltage available from a given zener diode
is temperature dependent, it is necessary to determine junc-
tiontemperatureunderanysetofoperatingconditionsinorder
to calculate its value. The following procedure is recom-
mended:
∆T is the increase in junction temperature above the lead
temperature and may be found from Figure 2 for a train of
power pulses (L = 3/8 inch) or from Figure 10 for dc power.
JL
∆T = θ
JL
P
D
JL
For worst-case design, using expected limits of I , limits of
Z
Lead Temperature, T , should be determined from:
L
P
and the extremes of T (∆T ) may be estimated. Changes
D
J J
T = θ
L
P
D
+ T
A
LA
in voltage, V , can then be found from:
Z
θ
P
is the lead-to-ambient thermal resistance (°C/W) and
LA
D
∆V = θ
∆T
J
VZ
is the power dissipation. The value for θ will vary and
LA
LA
depends on the device mounting method. θ
30–40°C/W for the various clips and tie points in common
is generally
θ
,thezenervoltagetemperaturecoefficient,isfoundfrom
VZ
Figures 5 and 6.
use and for printed circuit board wiring.
Under high power-pulse operation, the zener voltage will
vary with time and may also be affected significantly by the
zenerresistance. Forbestregulation, keepcurrentexcursions
as low as possible.
Data of Figure 2 should not be used to compute surge capa-
bility. Surge limitations are given in Figure 3. They are lower
than would be expected by considering only junction tempera-
ture, as current crowding effects cause temperatures to be ex-
tremely high in small spots resulting in device degradation
should the limits of Figure 3 be exceeded.
The temperature of the lead can also be measured using a
thermocoupleplacedontheleadascloseaspossibletothetie
point. The thermal mass connected to the tie point is normally
large enough so that it will not significantly respond to heat
surges generated in the diode as a result of pulsed operation
once steady-state conditions are achieved. Using the mea-
sured value of T , the junction temperature may be deter-
L
mined by:
T = T + ∆T
JL
J
L
Motorola TVS/Zener Device Data
1–3 Watt DO-41 Surmetic 30 Data Sheet
6-44
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