SLUAAT8 December   2023 CSD13201W10 , CSD13202Q2 , CSD13302W , CSD13303W1015 , CSD13306W , CSD13380F3 , CSD13381F4 , CSD13383F4 , CSD13385F5 , CSD15380F3 , CSD15571Q2 , CSD16301Q2 , CSD16321Q5 , CSD16322Q5 , CSD16323Q3 , CSD16325Q5 , CSD16327Q3 , CSD16340Q3 , CSD16342Q5A , CSD16401Q5 , CSD16403Q5A , CSD16404Q5A , CSD16406Q3 , CSD16407Q5 , CSD16408Q5 , CSD16409Q3 , CSD16410Q5A , CSD16411Q3 , CSD16412Q5A , CSD16413Q5A , CSD16414Q5 , CSD16415Q5 , CSD16556Q5B , CSD16570Q5B , CSD17301Q5A , CSD17302Q5A , CSD17303Q5 , CSD17304Q3 , CSD17305Q5A , CSD17306Q5A , CSD17307Q5A , CSD17308Q3 , CSD17309Q3 , CSD17310Q5A , CSD17311Q5 , CSD17312Q5 , CSD17313Q2 , CSD17318Q2 , CSD17322Q5A , CSD17327Q5A , CSD17381F4 , CSD17382F4 , CSD17483F4 , CSD17484F4 , CSD17501Q5A , CSD17505Q5A , CSD17506Q5A , CSD17507Q5A , CSD17510Q5A , CSD17522Q5A , CSD17527Q5A , CSD17551Q3A , CSD17551Q5A , CSD17552Q3A , CSD17552Q5A , CSD17553Q5A , CSD17555Q5A , CSD17556Q5B , CSD17559Q5 , CSD17570Q5B , CSD17571Q2 , CSD17573Q5B , CSD17575Q3 , CSD17576Q5B , CSD17577Q3A , CSD17577Q5A , CSD17578Q3A , CSD17578Q5A , CSD17579Q3A , CSD17579Q5A , CSD17581Q3A , CSD17581Q5A , CSD17585F5 , CSD18501Q5A , CSD18502KCS , CSD18502Q5B , CSD18503KCS , CSD18503Q5A , CSD18504KCS , CSD18504Q5A , CSD18509Q5B , CSD18510KCS , CSD18510KTT , CSD18510Q5B , CSD18511KCS , CSD18511KTT , CSD18511Q5A , CSD18512Q5B , CSD18513Q5A , CSD18514Q5A , CSD18531Q5A , CSD18532KCS , CSD18532NQ5B , CSD18532Q5B , CSD18533KCS , CSD18533Q5A , CSD18534KCS , CSD18534Q5A , CSD18535KCS , CSD18535KTT , CSD18536KCS , CSD18536KTT , CSD18537NKCS , CSD18537NQ5A , CSD18540Q5B , CSD18541F5 , CSD18542KCS , CSD18542KTT , CSD18543Q3A , CSD18563Q5A , CSD19501KCS , CSD19502Q5B , CSD19503KCS , CSD19505KCS , CSD19505KTT , CSD19506KCS , CSD19506KTT , CSD19531KCS , CSD19531Q5A , CSD19532KTT , CSD19532Q5B , CSD19533KCS , CSD19533Q5A , CSD19534KCS , CSD19534Q5A , CSD19535KCS , CSD19535KTT , CSD19536KCS , CSD19536KTT , CSD19537Q3 , CSD19538Q2 , CSD19538Q3A , CSD22202W15 , CSD22204W , CSD22205L , CSD22206W , CSD23202W10 , CSD23203W , CSD23280F3 , CSD23285F5 , CSD23381F4 , CSD23382F4 , CSD25202W15 , CSD25211W1015 , CSD25213W10 , CSD25304W1015 , CSD25310Q2 , CSD25402Q3A , CSD25404Q3 , CSD25480F3 , CSD25481F4 , CSD25483F4 , CSD25484F4 , CSD25485F5 , CSD25501F3 , CSD75207W15 , CSD75208W1015 , CSD83325L , CSD85301Q2 , CSD85302L , CSD85312Q3E , CSD86311W1723 , CSD87312Q3E , CSD87313DMS , CSD87501L , CSD87502Q2 , CSD87503Q3E , CSD88537ND , CSD88539ND

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Review the ZθJC Graph
  6. 3Using the ZθJC Graph to Estimate Junction Temperature Rise
  7. 4Application Example
  8. 5Using the ZθJC Graph to Estimate MOSFET Peak Current Capability
  9. 6Application Example
  10. 7Summary
  11. 8References

6 Application Example

Using the CSD19532Q5B, what is the peak current for a 1-ms single pulse at TC = 25°C? The ZθJC graph from the CSD19532Q5B is shown below in Figure 6-1.

GUID-D9F5A7F4-C677-4260-8CD7-F075D0D64956-low.png Figure 6-1 CSD19532Q5B ZθJC Graph

The CSD19532Q5B maximum continuous drain current is calculated as follows:

Equation 5. M a x   P D I S S ( T C = 25 ℃ ) = M a x   T J - 25 ℃ R θ J C = 150 ℃ - 25 ℃ 0.8 ℃ / W = 156 W
Equation 6. M a x   I D ( T C = 25 ℃ ) = M a x   P D I S S R D S ( o n ) @ M a x   T J

Maximum RDS(on) at TJ = 150°C can be calculated using the maximum specified RDS(on) = 4.9 mΩ at VGS = 10 V and multiplying RDS(on) by the normalizing factor shown in Figure 8 of the data sheet:

Equation 7. M a x   R D S ( o n ) @ M a x   T J = 4.9 m Ω × 2.1   = 10.3 m Ω
Equation 8. M a x   I D ( T A = 25 ℃ ) = 156 W 10.3 m Ω = 123 A

Draw a vertical line from 1 ms on the x-axis to the Single Pulse curve, and draw a horizontal line from there to the y-axis to get a value of ZθJC = 0.17. The peak drain current is calculated as follows:

Equation 9. P e a k   I D ( T C = 25 ℃ , t p = 1 m s ) = 150 ℃ - 25 ℃ 0.17 × 0.8 ℃ / W 10.3 m Ω = 299 A

These calculations assume that the case temperature can be held indefinitely at TC = 25°C. In reality, this is impossible without using an infinite heat sink with zero thermal impedance. A more realistic approach is to assume the maximum case temperature is equal to the maximum allowable PCB temperature. For an FR4, a typical maximum temperature is 110°C and the peak drain current is reduced:

Equation 10. P e a k   I D ( T C = 110 ℃ , t p = 1 m s ) = 150 ℃ - 110 ℃ 0.17 × 0.8 ℃ / W 10.3 m Ω = 169 A

What if the pulse width remains 1 ms but is repetitive with a duty cycle of 50%? From the ZθJC graph, the value of ZθJC = 0.56 for 1 ms, 50% duty cycle repetitive pulses. The peak repetitive drain current under these conditions is:

Equation 11. P e a k   r e p e t i t i v e   I D ( T C = 110 ℃ , t p = 1 m s , D = 50 % ) = 150 ℃ - 110 ℃ 0.56 × 0.8 ℃ / W 10.3 m Ω = 93 A

One last thing to note, for reliability purposes, most engineers typically derate the FET maximum operating junction temperature by 10°C to 25°C especially for repetitive pulses where the FET can operate for an extended period of time. For example, assume the derated maximum operating TJ = 130°C. Now, the peak repetitive drain current is:

Equation 12. P e a k   r e p e t i t i v e   I D ( T C = 110 ℃ , t p = 1 m s , D = 50 % ) = 130 ℃ - 110 ℃ 0.56 × 0.8 ℃ / W 10.3 m Ω = 66 A