Application Note - TVS

Application Note
Vishay General Semiconductor
Determining Clamping Voltage Levels
for a Broad Range of Pulse Currents
By Bruce Hartwig
Senior Automotive Applications Engineer
VC = (IP/IPP)(VC max. - VBR max.) + VBR max.
Where: IP = test pulse current
IPP = max rated pulse current
VC max. = maximum specified clamping voltage
VBR max. = upper limit of breakdown voltage
This calculation assumes a linear increase in VC between
VBR and VC max, which is realistic. Figure 1 illustrates the
DVC vs DIP relationship for two voltage levels, 10 V and
64 V, in the SMB 600 W series between VBR and VC as
determined by this formula. Results are linear as expected.
VBR max is used in this calculation as it is the upper limit of
specified breakdown voltage.
In those instances where VBR max is not given on the data
sheet, it can be closely approximated. For “A” suffix parts,
multiply the minimum VBR by 1.11 and for non-suffix parts,
multiply by 1.22 to obtain the maximum VBR. The curves
derived from measured data are compared with calculated
values in Figure 1. Surge tests were performed for a
30 piece sample at 25 °C ambient with a 10/1000 µs
waveform.
Note that the curves based on actual surge data have a
more shallow slope than those from the calculation,
indicating that the devices are conservatively rated and that
the formula shown provides a sufficient level of confidence
for worst-case design.
Document Number: 88446
Revision: 14-Aug-07
VC - Clamping Voltage (V)
This figure is easily calculated using the parameters on the
data sheet with the formula:
25
20
15
Calculated
Measured
SMBJ10A
10
0
25
50
75
100
IPP - Peak Pulse Current (%)
Figure 1. VC vs IPP for SMBJ10A Calculated and Measured
110
100
VC - Clamping Voltage (V)
In Transient Voltage Suppressor (TVS) data sheets, all
clamping voltage (VC) levels are specified at maximum
rated peak pulse current (IPP). How do you interpolate the
VC levels for transient currents (IP) other than the rated
maximum?
90
Calculated
80
Measured
70
60
50
SMBJ64A
40
0
25
50
75
100
IPP - Peak Pulse Current (%)
Figure 2. VC vs IPP for SMBJ64A Calculated and Measured
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