IGBT Gate Driver Calculation

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IGBT Gate Driver Calculation

• Gate Driver Requirement

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
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How to find the right gate resistor ?
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
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Difference between Trench- and SPT Technology

• 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

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Driver performance different IGBT technologies
needs different gate charge

• Trench IGBT with same chip current

Gate charge is 2.3 uC
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Driver performance different IGBT technologies
needs different gate charge

• SPT IGBT with same chip current

Gate charge is 3 uC
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• 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
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• 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
-8
? QG 1390nC
1390
Determination of Gate Charge
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• 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
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Power supply requirements

• 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

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• 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
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Pulse power rating of the gate resistor

• 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.
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• 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
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• 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_at_ Rg 7? R int
• IoutAV 13.9mA
• fsw 10kHz
• VCE 1200V
• QG 1390nC

Comparison with the parameters in the driver data
sheet
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• PCB Driver and PCB mountable Driver for single,
  half bridge, six pack modules
• integrated potential-free power supply
• switching frequency up to 100kHz
• output peak current up to 30A
• Gate charge up to 30µC
• dv/dt capability up to 75kV/µs
• high EMI immunity
• TTL- an CMOS-compatible inputs and outputs with
  potential isolation via opto coupler or
  transformer (isolation up to 4kVAC)
• protection (interlock, short pulse suppression,
  short circuit protection via VCE -monitoring,
  under voltage monitoring, error memory and error
  feedback)

SEMIDRIVER
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Product overview (important parameters)
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• Simple
• Adaptable
• Expandable
• Short time to market
• Two versions
• SKYPER (standard version)
• SKYPER PRO (premium version)

Driver core for IGBT modules
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• SKYPER
• Driver board
• SEMIX 3 IGBT half bridge
• with spring contacts

Assembly on SEMiXTM 3 Modular IPM
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take 3 for 6-packs
with adapter board
solder directly in your main board
modular IPM using SEMiX
SKYPER more than a solution
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Selection of the right IGBT driver

• Advice

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Problem 1--------------------- Cross conduction
Low impedance
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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
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• When the outer voltage potential V changes, the
  load Q has to follow
• This leads to a displacement current iV

IGBT - Parasitic capacitances
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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 gt VGE(th) then T2 turns on (Therefore
  SK recommends VGG- -5-8-15 V)

Switching Detailed for T2
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Problem 2 ----------------------------- gate
protection
Z 16 -18
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Gate clamping ---- how ?
Z18
PCB design because no cable
close to the IGBT
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Problem 3 -----------------booster for the gate
current
Use MOSFET for the booster
For small IGBTs is ok
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Problem 4 ---------------------------- Short
circuit

• 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

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Problem 5 dead time between top and bottom IGBT
Turn on and turn off delay must be symetrical
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Dead time explanation
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Dead time explanation

• 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 (2.5us1us) 1.5 us

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Our final recommendation

• 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
• Dont use bipolar transistors for the booster
• Protect the Gate/Emitter distance against over
  voltage
• Dont mix
• Peak current
• Gate charge

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Thanks