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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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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Date post:	25-Dec-2015
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1 Semikron Hong Kong Norbert Pluschke 07.10.2005 IGBT Gate Driver Calculation Gate Driver...

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