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For Si MOSFET IPD90N04S4L04.xls (infineon.com), the transient thermal impedance graph is as below 
Are all these curves for single pulse? Or repeated pulses?
I want to calculate the peak pulse current & power dissipation capacity for this MOSFET for specific pulse duration for repeated pulses. If above graph is for single pulses, then for repeated pulses how to calculate power dissipation ?
Solved! Go to Solution.
 Labels:

ispn:4466:1:0

l1:144:1:0

l2:152:1:0

l3:153:1:0
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Hi,
Thank you for contacting the Infineon tech support.
1) Are all these curves for single pulse? Or repeated pulses?
Soln: Thermal resistance (Rth) and thermal impedance (Zth) are related because the thermal resistance is the steadystate measure of how the device blocks heat flow. Thermal impedance is how the device responds to transient thermal events. It involves different thermal capacities of parts of the device and the thermal resistances between these parts. The given graph is for a single pulse as well for a repetitive pulses. The same graph has the Zthjc for a single pulse as well as for a pulse with a defined duty cycle. From this duty cycle and pulse time (which is nothing but the turn ON duration ) we can get the working switching frequency. It is used for calculating the peak power and verify with the SOA curve whether the given MOSFET is capable to handle such peak current rise.
2) I want to calculate the peak pulse current & power dissipation capacity for this MOSFET for specific pulse duration for repeated pulses. If above graph is for single pulses, then for repeated pulses how to calculate power dissipation ?
Soln: It can be calculated as follows,
Tj: Junction temp
rthjc : Junction to case thermal resistance ( this can be obtained from the referred graph at the required condition.)
Tc : Case temperature
Pd : Power dissipation
Tj = (rthjc*Pd) + Tc
From this we can calculate the required specs based on the current pulses as explained in previous section. The Tj shouldn't exceed 150C. Pd = Vd*Id
Regards,
Abhilash P
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Hi,
Thank you for contacting the Infineon tech support.
1) Are all these curves for single pulse? Or repeated pulses?
Soln: Thermal resistance (Rth) and thermal impedance (Zth) are related because the thermal resistance is the steadystate measure of how the device blocks heat flow. Thermal impedance is how the device responds to transient thermal events. It involves different thermal capacities of parts of the device and the thermal resistances between these parts. The given graph is for a single pulse as well for a repetitive pulses. The same graph has the Zthjc for a single pulse as well as for a pulse with a defined duty cycle. From this duty cycle and pulse time (which is nothing but the turn ON duration ) we can get the working switching frequency. It is used for calculating the peak power and verify with the SOA curve whether the given MOSFET is capable to handle such peak current rise.
2) I want to calculate the peak pulse current & power dissipation capacity for this MOSFET for specific pulse duration for repeated pulses. If above graph is for single pulses, then for repeated pulses how to calculate power dissipation ?
Soln: It can be calculated as follows,
Tj: Junction temp
rthjc : Junction to case thermal resistance ( this can be obtained from the referred graph at the required condition.)
Tc : Case temperature
Pd : Power dissipation
Tj = (rthjc*Pd) + Tc
From this we can calculate the required specs based on the current pulses as explained in previous section. The Tj shouldn't exceed 150C. Pd = Vd*Id
Regards,
Abhilash P
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Thanks Abhilash,
But, if the duty cycle is 90% or above 50% then this data is not mentioned in that graph (max thermal transient impedance). How to get the value of ZthJC for duty cycle of 90% ?
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Hi.
From the graph it can be seen that for duty above 50%, the graph is normalized to 1. Hence it is recommended to use the maximum Rthjc of the MOSFET at those conditions.
Regards,
Abhilash P
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Thanks Abhilash.
The SOA data given is at Tc = 25 deg. C.
Can I get SOA at Tc = 100 deg. C?
Also, max. power dissipation is given at Tc = 25 deg. C. as in below snap 
How can I know max. power dissipation at Tc = 100 deg C.?
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Hi,
Custom specific SOA has to be generated separately. Please contact your nearest sales office / FAE to get the data.
Regards,
Abhilash P