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IGBT Gate Driver Calculation

Gate Driver Requirement. IGBT Gate Driver Calculation. What is the most important requirement for an IGBT driver ?. Gate Peak current. Which gate driver is suitable for the module SKM 200 GB 128D ?.

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IGBT Gate Driver Calculation

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  1. Gate Driver Requirement IGBT Gate Driver Calculation

  2. What is the most important requirement for an IGBT driver ? Gate Peak current

  3. Which gate driver is suitable for the module SKM 200 GB 128D ? reverse recovery current Diode should be - 1.5 x I diode by 80 degree case 130A x 1.5 = 195A Design parameters: fsw = 10 kHz Rg = ? Gate resistor in range of “test – gate resistor” Conditions for a safety operation

  4. 195A – max reverse recovery current Rg = 7 Ohm Two gate resistors are possible for turn on and turn off Ron = 7 Ohm Roff = 10 Ohm How to find the right gate resistor ?

  5. Trench Technology needs a smaller Gate charge • Driver has to provide a smaller Gate charge • SPT Technology needs more Gate charge compared to Trench Technology • Driver has to provide a higher Gate charge Difference between Trench- and SPT Technology

  6. Trench IGBT with same chip current Gate charge is 2.3 uC Driver performance – different IGBT technologies needs different gate charge

  7. SPT IGBT with same chip current Gate charge is 3 uC Driver performance – different IGBT technologies needs different gate charge

  8. The suitable gate driver must provide the required • Gate charge (QG) – power supply of the driver must provide the average power • Average current (IoutAV) – power supply • Gate pulse current (Ig.pulse) – most important • at the applied switching frequency (fsw) Demands for the gate driver

  9. Gate charge (QG) can be determined from fig. 6 of the SEMITRANS data sheet The typical turn-on and turn-off voltage of the gate driver is VGG+ = +15V VGG- = -8V 15  QG = 1390nC -8 1390 Determination of Gate Charge

  10. Calculation of average current: • IoutAV = P / U V = +Vg + [-Vg] • with P = E * fsw = QG * V * fsw •  IoutAV = QG * fsw = 1390nC * 10kHz = 13.9mA Absolute value Calculation of the average current

  11. Gate charge • The power supply or the transformer must provide the energy (Semikron is using pulse transformer for the power supply, we must consider the transformed average power from the transformer) • Average current • Is related to the transformer Power supply requirements

  12. Examination of the peak gate current with minimum gate resistance • E.g. RG.on = RG.off = 7 • Ig.puls≈ V / RG + Rint= 23V / 7 + 1 = 2.9 A Calculation of the peak gate current

  13. P total – Gate resistor • Ppulse Gate resistor = I out AV x V • More information: The problem occurs when the user forgets about the peak power rating of the gate resistor. The peak power rating of many "ordinary" SMD resistors is quite small. There are SMD resistors available with higher peak power ratings. For example, if you take an SKD driver apart, you will see that the gate resistors are in a different SMD package to all the other resistors (except one or two other places that also need high peak power). The problem was less obvious with through hole components simply because the resistors were physically bigger. The Philips resistor data book has a good section on peak power ratings. Pulse power rating of the gate resistor

  14. The absolute maximum ratings of the suitable gate driver must be equal or higher than the applied and calculated values • Gate charge QG = 1390nC • Average current IoutAV = 13,9mA • Peak gate current Ig.pulse = 2.9 A • Switching frequency fsw = 10kHz • Collector Emitter voltage VCE = 1200V • Number of driver channels: 2 (GB module) • dual driver Choice of the suitable gate driver

  15. According to the applied and calculated values, the driver e. g. SKHI 22A is able to drive SKM200GB128D Calculated and applied values: • Ig.pulse = 2.9 A@ Rg = 7 + R int • IoutAV = 13.9mA • fsw = 10kHz • VCE = 1200V • QG = 1390nC Comparison with the parameters in the driver data sheet

  16. Product overview (important parameters)

  17. Simple • Adaptable • Expandable • Short time to market • Two versions • SKYPER™ (standard version) • SKYPER™ PRO (premium version) Driver core for IGBT modules

  18. SKYPER • Driver board • SEMIX 3 IGBT half bridge • with spring contacts Assembly on SEMiXTM 3 – Modular IPM

  19. take 3 for 6-packs with adapter board solder directly in your main board modular IPM using SEMiX® SKYPER™ – more than a solution

  20. Selection of the right IGBT driver Advice

  21. Low impedance Problem 1--------------------- Cross conduction

  22. vGE,T1(t) vGE,T2(t) VGG+ T1 D1 VGE, Io VGE(th) 0 t vCE,T1(t) iC,T1(t) VCC T2 D2 IO iv,T2 0 t vCE,T2(t) =vF,D2(t) iF,D2(t),iC,T2(t) VCC IO • Why changes VGE,T2 when T1 switches on? 0 t Cross conduction behavior

  23. When the outer voltage potential V changes, the load Q has to follow • This leads to a displacement current iV IGBT - Parasitic capacitances

  24. vCE,T2(t) VCC vGE,T2(t) VGG+ VGE(th) 0 t 0 iC,T2(t) iv,T2(t) t 0 t iC,T2 CGC,T2 iv,T2 vCE,T2 RGE,T2 vGE,T2 • Diode D2 switches off and takes over the voltage • T2 “sees” the voltage over D2 as vCE,T2 • With the changed voltage potential, the internal capacitances change their charge • The displacement current iv,T2 flows via CGC,T2, RGE,T2 and the driver • iv,T2 causes a voltage drop in RGE,T2 which is added to VGE,T2 • If vGE,T2 > VGE(th) then T2 turns on (Therefore SK recommends: VGG- = -5…-8…-15 V) Switching: Detailed for T2

  25. Z 16 -18 Problem 2 ----------------------------- gate protection

  26. Z18 PCB design because no cable close to the IGBT Gate clamping ---- how ?

  27. Use MOSFET for the booster For small IGBTs is ok Problem 3 -----------------booster for the gate current

  28. Over voltage • 1200V ----- is chip level ---- consider internal stray inductance • +/- 20V----- gate emitter voltage ---- consider switching behavior of freewheeling diode • Over current • Power dissipation of IGBT (short circuit current x time) • Chip temperature level Problem 4 ---------------------------- Short circuit

  29. Turn on and turn off delay must be symetrical Problem 5 – dead time between top and bottom IGBT

  30. Dead time explanation

  31. Example: • Dead time = 3 us logic level • Turn on delay 1 us • Turn off delay 2.5 us • Td – toff delay + ton delay = real dead time • Real dead time: 3us – (2.5us+1us) = 1.5 us Dead time explanation

  32. IGBT driver must provide the peak Gate current • The stray inductance should be very small in the gate driver circuit • Gate/Emitter resistor and Gate/Emitter capacitor (like Ciss) very close to the IGBT • Turn off status must have a very low impedance • High frequency capacitors very close to the IGBT driver booster • Don’t use bipolar transistors for the booster • Protect the Gate/Emitter distance against over voltage • Don’t mix; • Peak current • Gate charge Our final recommendation

  33. Thanks

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