Texas Instruments | DN-35 IGBT Drive Using MOSFET Gate Drivers (Rev. A) | Application notes | Texas Instruments DN-35 IGBT Drive Using MOSFET Gate Drivers (Rev. A) Application notes

Texas Instruments DN-35 IGBT Drive Using MOSFET Gate Drivers (Rev. A) Application notes
Application Report
SLUA169A – August 1995 – Revised June 2018
IGBT DRIVE USING MOSFET GATE DRIVERS
ABSTRACT
Insulated gate bipolar transistors (IGBTs) are gaining considerable use in circuits requiring high voltage
and current at moderate switching frequencies up to 100 kHz. Typically these circuits are in motor drive,
Uninterruptible Power Supply (UPS), Solar and other similar inverter applications. Much of the IGBTs
popularity stems from its simple MOSFET-like gate drive requirement. In comparison to bipolar transistors
(BJTs) which were formally used in such designs, the IGBT offers a considerable reduction in both size
and complexity of the drive circuitry as highlighted in Table 1. Modern IGBTs have the switching speed
suitable for power supply applications, thus IGBTs will compete with MOSFETs for certain high voltage
applications as well. Many designers have therefore turned to MOSFET drivers such as UCC2753x and
UCC53xx for their IGBT drive requirements.
Table 1. IGBT comparison
1
2
3
4
Characteristic
BJT
FET
IGBT
Power Rating
<10 kW
<10 kW
>10 kW
Drive
20uA
7 - 12V
15 - 20V
Switching Speed
Slow
Fast
Medium
Contents
IGBT drive requirements ....................................................................................................
Kelvin Connection ...........................................................................................................
Negative Turn-Off Bias ......................................................................................................
Isolated IGBT Driver ........................................................................................................
1
2
2
3
List of Figures
1
Miller Turn-On ................................................................................................................ 2
2
IGBT Bipolar Supply with Level Shifter ................................................................................... 3
3
UCC5390SCDEVM-010 Simplified Schematic........................................................................... 4
List of Tables
1
IGBT comparison ............................................................................................................ 1
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1
IGBT drive requirements
IGBT drive requirements can be divided into two basic application categories: 1) Those that apply high
dv/dt to the collector/emitter of the IGBT when it is off and 2) Those that do not. Examples of low dv/dt can
be found in non-synchronous buck regulators and two switch forward converters, where only one switch is
employed or multiple switches are activated synchronously in a bridge configuration. High dv/dt is applied
during the off-state in most bridge circuits such as inverters and motor controllers, when opposing devices
are turned on. Simultaneous cross conduction, or shoot through of opposing devices can occur in such
SLUA169A – August 1995 – Revised June 2018
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IGBT DRIVE USING MOSFET GATE DRIVERS
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1
Kelvin Connection
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bridge circuits, often with catastrophic results if proper gate drive and layout precautions are not followed.
This behavior is caused by parasitic collector to gate (miller) capacitance, effectively forming a capacitive
divider with the gate to emitter capacitance and thus inducing a gate to emitter voltage as illustrated in
Figure 1. Further information on IGBT drive requirements can be found in, SLUA618, Fundamentals of
MOSFET and IGBT Gate Driver Circuits.
VDS
VIN
Miller Turn-On Spike in VGS
Gate Driver
CGD
VGS of
RG
COSS
ISINK
ROL
CGS
VTH
MOSFET
ON OFF
VIN
VDS of
MOSFET
GND
Figure 1. Miller Turn-On
When high off-state dv/dt is not present, the IGBT can be driven like a MOSFET using any of the gate
drive circuits from switching power supplies. Normally 15V is applied gate to emitter during the on-state to
minimize saturation voltage. The gate resistor or gate drive current directly controls IGBT turn-on, however
turn-off is partially governed by minority carrier behavior and is less effected by gate drive.
2
Kelvin Connection
There are several techniques which can be employed to eliminate shoot through when high off-state dv/dt
is present. The most important technique, which should always be employed, is a Kelvin connection
between the IGBT emitter and the driver’s ground. High di/dt present in the emitter circuit can cause
substantial transient voltages to develop in the gate drive circuit if it is not properly referenced. The Kelvin
drive connection also minimizes the effective driver impedance for maximum attenuation of the dv/dt
induced gate voltage.
A Kelvin connection adds complication to driving multiple ground referenced IGBTs due to finite ground
circuit impedance. Substantial voltages may develop across the ground impedance during switching. This
ground bounce on power ground requires the gate driver to have a level shifter or isolation to reference
the input signal properly allowing Kelvin drive circuit connections.
3
Negative Turn-Off Bias
A Kelvin connected unipolar driver may often be adequate at lower switching speeds, however negative
gate bias must be applied during the off-state to utilize the IGBT at higher rates. This becomes apparent
considering that the gate to emitter threshold voltage drops to approximately 1.4 V at high temperature
due to negative temperature coefficient. With high dv/dt at the collector, a very low and impractical drive
impedance is required to assure that the device remains off. By utilizing a negative turn-off bias, an
adequate voltage margin is easily achieved, allowing the use of a more practical gate drive impedance.
Fortunately most gate drivers have sufficient voltage capability to be used with bipolar power supplies.
The UCC2753x shown in Figure 2 can sink up to 5 amps peak and is particularly suited to driving IGBTs.
For added reliability during power sequencing a low VDD clamp turns off the output, actively sinking
current when insufficient supply voltage is present. The positive supply, +Vcc, is normally 15 to 20 volts
and the negative supply, -VEE, typically ranges between -5 and -15 volts depending on circuit conditions.
Texas Instruments has the UCC2753x and UCC53xx families featuring strong sink current to defeat miller
turn on and the ability to drive IGBTs or MOSFETs up to 35V max supporting negative turn off capability.
2
IGBT DRIVE USING MOSFET GATE DRIVERS
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Isolated IGBT Driver
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UCC2753x
IN4
IN+
-13V
OUT
5
+
3
VDD
1
+
±
18 V
2
-13V
GND
+
±
13 V
-13V
GND
Figure 2. IGBT Bipolar Supply with Level Shifter
A PNP level shift circuit references the drive signal to ground. Opto-couplers are also commonly
employed, and may be interfaced directly to the gate driver by referencing the signal to the negative
supply. Note that high dv/dt is a very demanding application for optocouplers, and only devices rated for
high CMRR should be used such as UCC53xx isolated gate drivers.
4
Isolated IGBT Driver
A bipolar IGBT gate driver with isolated bias supply can be implemented using the UCC53xx isolated gate
driver as featured in UCC5390SCDEVM-010 shown in Figure 3. The UCC53xx transmits the gate drive
signal across the isolation barrier and SN6505B transmits power across a push pull transformer, thereby
achieving low cost and high voltage isolation in a compact solution. An additional transformer winding
develops a negative voltage, providing a bipolar supply for the UCC53xx. The UCC53xx can also be used
for circuits which do not require negative turn-off bias by simply eliminating the negative supply and using
a positive isolated bias to drive the IGBT gate.
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3
Isolated IGBT Driver
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VCC1
UCC53xx
1
VCC1
2
IN+
OUTH 6
3
IN-
OUTL 7
4
GND1
VEE2
VCC2
5
8
GND1
VCC1
SN6505B
VCC2
1
VCC
D1
5
2
EN
D2
6
3
CLK
GND
7
VCC1
Source
GND2
GND1
Figure 3. UCC5390SCDEVM-010 Simplified Schematic
4
IGBT DRIVE USING MOSFET GATE DRIVERS
SLUA169A – August 1995 – Revised June 2018
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Copyright © 1995–2018, Texas Instruments Incorporated
Revision History
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Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from original Revision (March 2013) to A Revision ........................................................................................ Page
•
•
•
Added Updated figure for IGBT Miller Turn-On ....................................................................................... 2
Added Level Shift input and negative bias for UCC2753x driving IGBT ........................................................... 3
Added Isolated Gate Driver with Isolated negative bias for UCC5390SCDEVM driving IGBT ................................. 4
SLUA169A – August 1995 – Revised June 2018
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Copyright © 1995–2018, Texas Instruments Incorporated
Revision History
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