Texas Instruments | Implementing a Bipolar Gate Drive for Low-Side IGBTs and SiC FETs in Motor Drive | Application notes | Texas Instruments Implementing a Bipolar Gate Drive for Low-Side IGBTs and SiC FETs in Motor Drive Application notes

Texas Instruments Implementing a Bipolar Gate Drive for Low-Side IGBTs and SiC FETs in Motor Drive Application notes
Implementing a Bipolar Gate Drive for Low-Side IGBTs
and SiC FETs in Motor Drives Applications
Mamadou Diallo, High Power Drivers
BLDC Motor Drives applications such as pumps and
compressors use three-phase inverters in their power
modules to convert the rectified DC power to AC
power necessary to control the speed, torque, and
direction of the AC motors. IGBTs are the basic
building blocks of the inverter stage which, in some
cases, require a bipolar or unipolar gate drive supply
to drive the low-side IGBT. When implementing a
bipolar power supply to turn off the IGBTs, a level
shifter is required to interface between the controller,
referenced to GND, while the driver IC is referenced to
negative power supply. This tech note discusses how
to implement a level-shifter network to allow a bipolar
gate drive, which is critical to safely turn off the lowside IGBT.
Low-Side Gate Driver Selection
The control architecture in Figure 1 is common
practice in BLDC motor drives applications (< 5 kW)
where the controller shares the same ground with the
IGBTs in the inverter stage. This architecture allows
the reinforced isolation to be implemented on the
communication channels, as shown in Figure 1, and
reduces the number of reinforced isolation gate
drivers. This enables driving the low-side IGBTs
without isolation while driving the high-side IGBTs with
a functional isolated driver. This ensures a costoptimized, compact solution where non-isolated, lowside gate drivers can effectively drive each of the three
legs of the low-side IGBTs. The UCC27531 and family
are available in SOT23 6-pin packages and have a
wide VDD voltage range (10 to 35 V), suitable for IGBTs
that require a unipolar (+15 V / 0 V) or bipolar gate
drive voltage (+15 V / -8 V).
Figure 1. System Block Diagram
Unipolar Supply Operation
Some applications (low to medium power) use a
unipolar gate drive with VDD=15–18 V and VDC- = 0V
to drive the IGBTs, in which case both the emitter of
the IGBT, the MCU, as well as the gate driver and the
decoupling capacitor of the gate driver CVDD are
referenced to the same 0-V ground.
Figure 2. Simulations Schematic
Bipolar Supply Operation
SLUA994 – October 2019
Submit Documentation Feedback
Implementing a Bipolar Gate Drive for Low-Side IGBTs and SiC FETs in
Motor Drives Applications Mamadou Diallo, High Power Drivers
Copyright © 2019, Texas Instruments Incorporated
1
References
www.ti.com
For medium to high power applications where the gate
driver does not have the Miller clamp feature, there is
a risk of Miller-induced turn-on when a high dv/dt is
seen across the collector-to-emitter junctions of the
IGBT. Leakage current in the form of ICG = CCG*dVCE/dt
can couple at the gate, which can charge the gate
voltage beyond the threshold of the IGBT. To
overcome this issue, designers can use a bipolar gate
drive operation where the negative voltage (VGE = -5 to
-8V) ensures that the collector-to-gate charge is lower
than the gate to-emitter’s to keep the IGBT fully off. To
implement this, there are couples of key
considerations to drive the low-side IGBT with a
negative voltage.
Because both the low-side gate driver and low-side
IGBT are referenced to the negative voltage supply, a
level-shifter network is therefore required to interface
the MCU signal, referenced to 0 V, and the gate driver
IC, referenced to -8 V.
The schematic in Figure 2 shows the PWM signal (0 to
3.3 V) referenced to 0 V while the driver GND pin is
referenced to the -8-V negative supply necessary to
fully turn off the IGBT. A low-cost PNP transistor in an
emitter base configuration allows the control signal to
interface with the input stage of the driver. In this
configuration, the emitter is connected to the PWM
signal with a resistor R3 setting the current through the
transistor. The base voltage is negatively biased with
respect to the emitter, while the collector resistor R4
(optional) helps dissipate power away from the
transistor. C8 is used to provide the peak current
necessary to turn on the IGBT while also filtering noise
on the supply pin of the driver. This capacitor,
referenced to the negative supply -8 V, in practice
must be placed directly across the VDD pin of the
driver. The EN pin of the driver left floating in this
application ensures that this pin is internally pulled
high through a 500-kΩ resistor. This EN pin is
convenient for battery-powered applications to disable
the driver and set it in a low current standby mode.
Figure 3 shows the PWM signal referenced to the 0-V
controller ground while the driver input signal sees a
PWM signal from -5.42 V to -8 V. AM2 captures the
current through the level-shifter; this current is based
on the power dissipation capability of the transistor,
bandwidth, and desired prop delay. The VGE at the
output of the driver provides the positive gate voltage
to turn on the IGBT/SiC and the negative voltage to
keep the FET off during high dv/dt transitions.
Figure 3. Simulation Results
Table 1. Alternate Devices
1
UCC27531
UCC27533
UCC27536
UCC27537
UCC27538
UCC27532
Current
Source/Sink
2.5 A / 5 A
2.5 A / 5 A
2.5 A / 5 A
2.5 A / 5 A
2.5 A / 5 A
2.5 A / 5 A
Single
IN
Single
Dual
Single
Single
Dual
EN
Yes
No
Yes
Yes
No
Yes
Output
Split
Single
Single
Single
Split
Split
Inverting
No
Yes
Yes
No
No
No
References
Texas Instruments, Gate Driver Overview Page
Texas Instruments, UCC27531 Product Page
Texas Instruments, UCC27531 EVM Page
1.1
Trademarks
All trademarks are the property of their respective owners.
2
Implementing a Bipolar Gate Drive for Low-Side IGBTs and SiC FETs in
Motor Drives Applications Mamadou Diallo, High Power Drivers
Copyright © 2019, Texas Instruments Incorporated
SLUA994 – October 2019
Submit Documentation Feedback
IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE
DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY
IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable
standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you
permission to use these resources only for development of an application that uses the TI products described in the resource. Other
reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third
party intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims,
damages, costs, losses, and liabilities arising out of your use of these resources.
TI’s products are provided subject to TI’s Terms of Sale (www.ti.com/legal/termsofsale.html) or other applicable terms available either on
ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable
warranties or warranty disclaimers for TI products.
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2019, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Related manuals

Download PDF

advertising