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Semikron Hong Kong
Gate Driver Requirement
IGBT Gate Driver Calculation
Norbert Pluschke 07.10.2005
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for an
IGBT driver ?
Gate Peak current
Norbert Pluschke 07.10.2005
Semikron Hong Kong
What is the most important requirement
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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”
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
Conditions for a safety operation
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Semikron Hong Kong
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 ?
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 Trench Technology needs 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 has to provide a smaller Gate charge
Difference between Trench- and SPT Technology
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Gate charge is 2.3 uC
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 Trench IGBT with same chip current
Driver performance – different IGBT technologies
needs different gate charge
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Gate charge is 3 uC
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 SPT IGBT with same chip current
Driver performance – different IGBT technologies
needs different gate charge
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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
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
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
Semikron Hong Kong

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VGG+ = +15V
VGG- = -8V
 QG = 1390nC
-8
1390
Determination of Gate Charge
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Calculation of average current:

IoutAV = P / U

with P = E * fsw = QG * V * fsw
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
V = +Vg + [-Vg]
Absolute value

 IoutAV = QG * fsw
= 1390nC * 10kHz = 13.9mA
Calculation of the average current
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 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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 Gate charge
Power supply requirements
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Examination of the peak gate current with minimum
gate resistance

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
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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 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.
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 P total – Gate resistor
The Philips resistor data book has a good section on peak power ratings.
Pulse power rating of the gate resistor
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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
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
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
@ Rg = 7 + R int

IoutAV = 13.9mA

fsw = 10kHz

VCE = 1200V

QG = 1390nC
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
Comparison with the parameters in the driver data sheet
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Product overview (important parameters)
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 Adaptable
 Expandable
 Short time to market
 Two versions
 SKYPER™ (standard version)
 SKYPER™ PRO (premium version)
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 Simple
Driver core for IGBT modules
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 Driver board
 SEMIX 3 IGBT
half bridge
with spring
contacts
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 SKYPER
Assembly on SEMiXTM 3 – Modular IPM
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with adapter
board
solder directly in
your main board
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take 3
for 6-packs
modular IPM
using SEMiX®
SKYPER™ – more than a solution
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Advice
Norbert Pluschke 07.10.2005
Semikron Hong Kong
Selection of the right IGBT driver
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Low impedance
Problem 1--------------------- Cross conduction
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VGG+
VGE, Io
VGE(th)
T1
D1
T2
D2
0
vCE,T1(t)
iC,T1(t)
t
VCC
IO
iv,T2
0
vCE,T2(t) = vF,D2(t)
iF,D2(t), iC,T2(t)
t
VCC
IO
0
t
 Why changes
VGE,T2 when T1
switches on?
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vGE,T1(t)
vGE,T2(t)
Cross conduction behavior
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iv  C 
dv
dt
 When the outer voltage potential V changes, the load Q has to follow
 This leads to a displacement current iV
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Q  CV
IGBT - Parasitic capacitances
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vCE,T2(t)
VCC
CGC,T2
iC,T2
t
iC,T2(t)
iv,T2(t)
iv,T2
vCE,T2
0
t
vGE,T2(t) VGG+
RGE,T2
vGE,T2
dv CE,T2
iv,T2  CGC,T2 
dt
v GE,T2  iv,T2  RGE,T2
VGE(th)
0
t





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
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 If vGE,T2 > VGE(th) then T2 turns on (Therefore SK recommends: VGG- = -5…-8…-15 V)
Switching: Detailed for T2
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Semikron Hong Kong
Z 16 -18
Problem 2 ----------------------------- gate protection
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Semikron Hong Kong
Z18
PCB design because no cable
close to the IGBT
Gate clamping ---- how ?
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Semikron Hong Kong
Use MOSFET for the booster
For small IGBTs is ok
Problem 3 -----------------booster for the gate current
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 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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 Over voltage
Problem 4 ---------------------------- Short circuit
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Turn on and turn off delay must be
symetrical
Problem 5 – dead time between top and bottom IGBT
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Dead time explanation
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 Example:
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 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
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 Peak current
 Gate charge
Semikron Hong Kong
 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;
Our final recommendation
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Semikron Hong Kong
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