1 Semikron Hong Kong Norbert Pluschke 07.10.2005 IGBT Gate Driver Calculation Gate Driver...
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Transcript of 1 Semikron Hong Kong Norbert Pluschke 07.10.2005 IGBT Gate Driver Calculation Gate Driver...
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Norbert Pluschke 07.10.2005
IGBT Gate Driver Calculation
Gate Driver Requirement
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What is the most important requirement
for an
IGBT driver ?
Gate Peak current
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Conditions for a safety operation
Which gate driver is suitable for the module SKM 200 GB 128D ?
Design parameters:
fsw = 10 kHz
Rg = ?
reverse recovery current Diode should be - 1.5 x I diode by 80 degree case 130A x 1.5 = 195A
Gate resistor in range of “test – gate resistor”
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How to find the right gate resistor ?
Rg = 7 OhmTwo gate resistors are possible for turn on and turn offRon = 7 OhmRoff = 10 Ohm
195A – max reverse recovery current
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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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Norbert Pluschke 07.10.2005
Driver performance – different IGBT technologies needs different gate charge
SPT IGBT with same chip current
Gate charge is 3 uC
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Demands for the gate driver
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)
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-8
15
1390
Determination of Gate Charge
Gate charge (QG) can be determined from fig. 6 of the SEMITRANS data sheet
QG = 1390nC
The typical turn-on and turn-off voltage of the gate driver is
VGG+ = +15V
VGG- = -8V
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Calculation of the average current
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
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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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Calculation of the peak gate current
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
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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 ratingof the gate resistor. The peak power rating of many "ordinary" SMD resistors is quite small. There are SMD resistors available with higher peak powerratings. For example, if you take an SKD driver apart, you will seethat the gate resistors are in a different SMD package to all the otherresistors (except one or two other places that also need high peak power). Theproblem was less obvious with through hole components simply because theresistors were physically bigger.
The Philips resistor data book has a good section on peak power ratings.
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Choice of the suitable gate driver
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
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Comparison with the parameters in the driver data sheet
Calculated and applied values:
Ig.pulse = 2.9 A@ Rg = 7 + R int
IoutAV = 13.9mA
fsw = 10kHz
VCE = 1200V
QG = 1390nC
According to the applied and calculated values, the driver e. g. SKHI 22A is able to drive SKM200GB128D
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Product overview (important parameters)
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Driver core for IGBT modules
Simple
Adaptable
Expandable
Short time to market
Two versions SKYPER™ (standard version)
SKYPER™ PRO (premium version)
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Assembly on SEMiXTM 3 – Modular IPM
SKYPER Driver board
SEMIX 3 IGBT half bridgewith spring contacts
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SKYPER™ – more than a solution
modular IPM using SEMiX®
with adapter board
solder directly in your main board
take 3 for 6-packs
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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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Cross conduction behavior
vCE,T1(t)iC,T1(t)
VCC
IO
0t
vGE,T1(t)vGE,T2(t)
VGE, Io
VGE(th)
0t
VGG+
VCC
IO
0t
vCE,T2(t) = vF,D2(t)iF,D2(t), iC,T2(t)
T1 D1
T2 D2iv,T2
Why changes VGE,T2 when T1 switches on?
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IGBT - Parasitic capacitances
dtdv
Ci
VCQ
v
When the outer voltage potential V changes, the load Q has to follow This leads to a displacement current iV
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Switching: Detailed for T2
dt
dvCi T2CE,
T2GC,T2v,
iv,T2
T2GE,T2v,T2GE, Riv
vCE,T2
vGE,T2
iC,T2
RGE,T2
CGC,T2
vCE,T2(t) VCC
0t
0t
iC,T2(t)iv,T2(t)
vGE,T2(t)
VGE(th)
0t
VGG+
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)
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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 besymetrical
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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 – (2.5us+1us) = 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 Don’t use bipolar transistors for the booster Protect the Gate/Emitter distance against over voltage Don’t mix;
Peak current Gate charge
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