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Bridging Theory in Practice

Bridging Theory in Practice. Transferring Technical Knowledge to Practical Applications. Advanced Power Dissipation and AC Thermal Analysis. Advanced Power Dissipation and AC Thermal Analysis. Intended Audience:

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Bridging Theory in Practice

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  1. Bridging Theory in Practice Transferring Technical Knowledge to Practical Applications

  2. Advanced Power Dissipation and AC Thermal Analysis

  3. Advanced Power Dissipation and AC Thermal Analysis Intended Audience: • Engineers interested in advanced thermal design under AC (variable duty cycle and transient) conditions • A basic knowledge of DC thermal analysis is required Topics Covered: • Modeling thermal performance with electrical parameters • Explanation of thermal RC networks • Introduction of the Zth Diagram • AC thermal calculations • Complex waveform (superposition principle) thermal calculations Expected Time: • Approximately 60 minutes

  4. Advanced Power Dissipation and AC Thermal Analysis • Electrical Parameters vs. Thermal Parameters • Thermal Resistance and Capacitance Networks • Understanding the Zth Diagram • Example AC Thermal Calculations • Complex Waveforms and Superposition

  5. Electrical vs. Thermal DC Parameters Electrical Parameters Thermal Parameters + + V T R Rth I PD - - V = I R R = Electrical Resistance () V = Potential Difference (V) I = Current (A) T = PD Rth Rth = Thermal Resistance (C/W) T = Temperature Difference (C) PD = Power Dissipated (W)

  6. Electrical Resistance vs. Thermal Resistance Electrical Resistance Thermal Resistance PD I A A + + } d } d T V - - R Rth  th I = Current A = Area d = Thickness  = Electrical Conductivity R = Electrical Resistance () PD = Power Dissipated A = Area d = Thickness th = Thermal Conductivity Rth = Thermal Resistance (C/W)

  7. Electrical Circuits vs. Thermal Circuits Electrical Circuits Thermal Circuits + + V T R Rth I PD - - I = 10A R = 1 V = IR V = (10A)(1) = 10V 10V Potential Difference PD = 10W Rth = 1C/W T = PDRth T = (10W)(1C/W) = 10C 10C Temperature Difference

  8. Electrical vs. Thermal Parameters + + T V E Q Cth C - - Electrical Parameters Thermal Parameters C = Capacitance (Farads = A-sec / V) Cth = Thermal Capacitance (Joules / C = Watts-sec / C)

  9. Advanced Power Dissipation and AC Thermal Analysis • Electrical Parameters vs. Thermal Parameters • Thermal Resistance and Capacitance Networks • Understanding the Zth Diagram • Example AC Thermal Calculations • Complex Waveforms and Superposition

  10. Thermal Resistance & Capacitance p+ Well Cth1 - Rth1 Silicon Cth2 – Rth2 Example Silicon Wafer Cross Section Die Attach Cth3 – Rth3 Leadframe Metal Leadframe

  11. Thermal RC Network - Internal Rth1 Rth2 Rth3 Tjunction PD Chip T Cth1 Cth2 Cth3 Temperature ~ Voltage Power ~ Current Tambient

  12. Thermal RC Network – Total Rth1 Rth2 Rth3 Rinteface Rheatsink Tjunction Tcase PD Chip T Cth1 Cth2 Cth3 Cinterface Cheatsink Heatsink Tambient Temperature ~ Voltage Power ~ Current

  13. Junction Temperature Calculations Rth1 Rth2 Rth3 Tjunction Tcase PD Chip T Cth1 Cth2 Cth3 Heatsink Tambient With temperature analogous to voltage, T Is determined by the PD and the RC network

  14. Junction Temperature Calculations Rth1 Rth2 Rth3 Tjunction Tcase PD Chip T Cth1 Cth2 Cth3 Heatsink Tambient The maximum junction temperature is specified in the absolute maximum section of the data sheet (Tj,max)

  15. Junction Temperature Calculations Tjc Rth1 Rth2 Rth3 Tjunction Tcase PD Chip T Cth1 Cth2 Cth3 Heatsink Tambient The device junction-to-case thermal resistance (Rthjc) is specified in the datasheet and determines Tjc. Rthjc is usually valid for DC only

  16. Junction Temperature Calculations Tca Rth1 Rth2 Rth3 Tjunction Tcase PD Chip T Cth1 Cth2 Cth3 Heatsink Tambient The external case-to-ambient thermal resistance, (Rthca) is determined by the heatsink. This determines the temperature change from the case to the ambient.

  17. DC Junction Temperature Calculations Rth1 Rth2 Rth3 Tjunction Tcase PD Chip T Heatsink Tambient Under DC conditions, power and temperature reach steady state conditions and the thermal capacitors are removed from the circuit model

  18. DC Junction Temperature Calculation • Power Dissipation PD = Ids2Rdson = (5A)2(24m) = 0.6W • Thermal Resistance Rthja = 55 C/W • Junction Temperature Tjunction = Tambient + PDRthja Tjunction = 85C + (0.6W)(55C/W) Tjunction = 85C + 33C = 118C DC Calculations are relatively simple

  19. AC Junction Temperature Calculation of Transfer Function Rth1 Rth2 Rth3 Tjunction Tcase PD Chip T Cth1 Cth2 Cth3 Zth(j) = ? Zth(t) = ? Heatsink Tambient

  20. AC Junction Temperature Calculation of Transfer Function

  21. Simplified AC Thermal RC Network R’th1 R’th2 R’th3 Tjunction Tcase PD Chip T C’th1 C’th2 C’th3 Heatsink Tambient Thermal capacitance now in parallel with thermal resistance

  22. Simplified AC Thermal RC Network R’th1 R’th2 R’th3 Tjunction Tcase PD Chip T C’th1 C’th2 C’th3 Heatsink Tambient The new RC component values of the simplified network are obtained by mathematical transformations. They do NOT refer to any physical layer. Together, they describe the overall thermal behavior and performance of the device and heatsink.

  23. Simplified AC Thermal RC Network R’th1 R’th2 R’th3 Tjunction Tcase PD Chip T C’th1 C’th2 C’th3 Frequency Domain Heatsink Tambient Time Domain

  24. Zth P(t) Tj(t) AC Temperature Calculation Simplified Transfer Function T(t)=PD(t)Zth(t)

  25. Advanced Power Dissipation and AC Thermal Analysis • Electrical Parameters vs. Thermal Parameters • Thermal Resistance and Capacitance Networks • Understanding the Zth Diagram • Example AC Thermal Calculations • Complex Waveforms and Superposition

  26. Create test set-up for integrated circuit package types Power is generated in the integrated circuit for defined lengths of time The resulting temperature rise is measured A thermal impedance (Zth) diagram is generated Zth P(t) Tj(t) Development of the Zth Diagram

  27. 100.0 10.0 1.0 Zthja (C / W) Duty Cycle 50% 20% 0.1 10% 5% 2% 1% Single Pulse 0.01 tpulse (sec) 1E-5 1E-3 1E-1 1E+1 1E+3 Zth Diagram for the TO-263 Package

  28. P(t) PD tpulse Duty Cycle 50% 20% 10% 5% 2% 1% Single Pulse Zth Diagram for the TO-263 Package 100.0 Single Pulse 10.0 1.0 Zthja (C / W) 0.1 0.01 tpulse (sec) 1E-5 1E-3 1E-1 1E+1 1E+3

  29. P(t) PD tpulse T Duty Cycle 50% 20% 10% 5% 2% 1% Zth Diagram for the TO-263 Package 100.0 Periodic event: 10.0 1.0 Zthja (C / W) Duty Cycle: 0.1 Single Pulse 0.01 tpulse (sec) 1E-5 1E-3 1E-1 1E+1 1E+3

  30. Zth Diagrams for Different Packages TO-263-5-1 tp = 1s Zthja 2C/W TO-252-3-1 tp = 1s Zthja 4C/W SOT-223 tp = 1s Zthja 30C/W SO-8 tp = 1s Zthja 65C/W

  31. Advanced Power Dissipation and AC Thermal Analysis • Electrical Parameters vs. Thermal Parameters • Thermal Resistance and Capacitance Networks • Understanding the Zth Diagram • Example AC Thermal Calculations • Complex Waveforms and Superposition

  32. Single Pulse in aTO-263 Package PD tpulse 400W tpulse = 200µs Tiunction(t) Tpeak Tpeak = ? 25C

  33. Duty Cycle 50% 20% 10% 5% 2% 1% Single Pulse Single Pulse in aTO-263 Package 100.0 10.0 tpulse = 2E-4 s Zthja  0.083 C/W 1.0 Zthja (C / W) Duty Cycle 50% 20% 0.1 10% 5% 2% 1% Single Pulse 0.01 tpulse (sec) 1E-5 1E-3 1E-1 1E+1 1E+3

  34. Power Dissipation PD = 400W Thermal Resistance Zthja = 0.083 C/W Junction Temperature Tjunction,peak = Tambient + PDZthja Tjunction,peak = 25C + (400W)(0.083C/W) Tjunction,peak = 25C + 33C = 58C Single Pulse in aTO-263 Package

  35. Single Pulse – TO-263 Package Saber Simulation 55C 400W 350W 50C 300W Tjunction,peak = 55C 45C 250W 200W 40C 150W 35C 100W 30C PD,max = 400W 50W 25C 0W 0 100 200 300 400 500 600 700 Time (s)

  36. 50% Duty Cycle in aTO-263 Package tpulse = 200µs PD 1.44W tperiod = 400µs Tiunction(t) Tpeak Tpeak = ? 25C

  37. tpulse = 2E-4 s Zthja  23 C/W 50% Duty Cycle in aTO-263 Package 100.0 10.0 1.0 Zthja (C / W) Duty Cycle 50% 20% 0.1 10% 5% 2% 1% Single Pulse 0.01 tpulse (sec) 1E-5 1E-3 1E-1 1E+1 1E+3

  38. 50% Duty Cycle in aTO-263 Package • Power Dissipation PD = 1.44W • Thermal Resistance Zthja = 23 C/W • Junction Temperature Tjunction = Tambient + PDZthja Tjunction = 25C + (1.44W)(23C/W) Tjunction = 25C + 33C = 58C

  39. Advanced Power Dissipation and AC Thermal Analysis • Electrical Parameters vs. Thermal Parameters • Thermal Resistance and Capacitance Networks • Understanding the Zth Diagram • Example AC Thermal Calculations • Complex Waveforms and Superposition

  40. Complex Pulse-SuperpositionMOSFET Turn On • VIN goes HI • IDS increases • VDS decreases • PLOSS spikes 1. VIN 4. PLOSS 2. IDS 3. VDS IDS

  41. Complex Pulse-SuperpositionMOSFET Turn On Pulse 1: tSTART 20µS tSTOP 50µS Pulse 2: tSTART 25µS tSTOP 50µS Pulse 3(neg): tSTART 40µS tSTOP 50µS Pulse 4(neg): tSTART 45µS tSTOP 50µS 1. VIN 4. PLOSS 2. IDS 3. VDS IDS

  42. Complex Pulse-SuperpositionMOSFET Turn On t=5µs At t = 5µs: tPULSE,1 = 5µsec tPULSE,2 = tPULSE,3 = tPULSE,4= 0 TJ1(5µs) = ZTH(5µs)*PPULSE,1 Power Time

  43. Complex Pulse-SuperpositionMOSFET Turn On t=20µs At t = 20µs: tPULSE,1 = 20µsec tPULSE,2 = 15µsec tPULSE,3= tPULSE,4 = 0 TJ2(20µs) = ZTH(20µs)*PPULSE,1 + ZTH(15µs)*PPULSE,2 Power Time

  44. Complex Pulse-SuperpositonMOSFET Turn On t=25µs At t = 25µs: tPULSE,1 = 25µsec tPULSE,2 = 20µsec tPULSE,3 = 5µsec tPULSE,4 = 0 TJ3(25µs) = ZTH(25µs)*PPULSE,1 + ZTH(20µs)*PPULSE,2 - ZTH(5µs)*PPULSE,3 Power Time

  45. Complex Pulse-SuperpositonMOSFET Turn On t=30µs At t = 30µs: tPULSE,1 = 30µsec tPULSE,2 = 25µsec tPULSE,3 = 10µsec tPULSE,4 = 5µsec TJ4(30µs) = ZTH(30µs)*PPULSE,1 + ZTH(25µs)*PPULSE,2 - ZTH(10µs)*PPULSE,3 - ZTH(5µs)*PPULSE,4 Power Time

  46. Complex Pulse-SuperpositonMOSFET Turn On Pulse 1: tSTART 20µS tSTOP 50µS Pulse 2: tSTART 25µS tSTOP 50µS Pulse 3(neg): tSTART 40µS tSTOP 50µS Pulse 4(neg): tSTART 45µS tSTOP 50µS TJ2 TJ1 TJ3 4. PLOSS TJ4 IDS

  47. Advanced Power Dissipation and AC Thermal Analysis • Electrical Parameters vs. Thermal Parameters • Thermal Resistance and Capacitance Networks • Understanding the Zth Diagram • Example AC Thermal Calculations • Complex Waveforms and Superposition

  48. Advanced Power Dissipation and AC Thermal Analysis

  49. Thank you! www.btipnow.com

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