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 www.vishay.com 283