Solutions for High Voltage Drives
Identifying proper Gate Drivers for Power SwitchingandDifferentiating Isolation techniques
December 2020

Content and Presenters
Introduction
Powers Switches differences and why Gate Drivers are need it:

Differences & Similarities between IGBT’s, MOSFET’s, SiC MOSFET’s & GaN MOSFET’s
Gate Drive requirements for Power Switches needs

Gate Drivers tech features overview
Top Key Parameters for Gate Drivers
Gate Drivers selection process

Gate Drivers Categories/Types
High Side, Low Side, Dual… etc…

Non-isolated Gate Drivers & relationship to Power Switches
Isolated Gate Driver and their Applications




2

Types of Isolation and PROS/CONS of each
Why Isolate, how to Isolate and Apps
Isolation Standards

Gate Drivers Tech/Market & Applications Executive Summary
Gate drivers technologies have had certain evolutions during the last decadeWith the arrival of on-chip integrated isolation technologies, isolated driver ICs have been developed by main driver IC
manufacturers.
These digital isolators are replacing the OPTO-coupler technology little bylittle
So far, microtransformers (coreless transformers) are the preferred digital isolation

In the next 5 years, evolving industry needs will have a considerable impact on gate drivers as well:The emerging market of 48V mild hybrid will require isolated half-bridge drivers. Until now, there was no need for isolation in such low voltages. The cost of
microtransformers manufactured today will decrease considerably.
SiC MOSFETs will also have an impact on the gate driver market in two ways:
 Plug-and-Play market will enjoy a short term growth as some clients may choose to integrate SiC in their new generation converters. Customers
encountering difficulties with the development of adequate drivers will prefer to purchase plug & play ones to accelerate the integration of SiC.
 New safety and monitoring functions will be proposed by driver IC and gate driver board manufacturers in order to enhance the performance and thereliability of SiC switches.

Beyond 2025In a longer term perspective, high temperature (HT) driver ICs will see a much bigger market, being driven by integrations into high power modules. Currently,
the aerospace industry is developing HT modules, and in the coming years it will be extended to wind turbines, rail traction, electric cars, inverters, etc.
This integration trends will also appear on SiC IPMs, where the need to have the driver IC closer to the SiC MOSFETs will end up integrating them on thesame package.



3

Driving Force in power management

Highestefficiency

Lowestnoise
OptimalPower
Solution

Smallersize

Lowestcost

Applications
For switched-mode power electronic applications involved in high-power andhigh-voltage conversion

Factory automation

Motor drive and control

Enterprise power
power && telecom
Enterprisetelecom

Smart grid

Automotive

Other industrials

Gate Drivers Requirements for Power Switching Devices
 MOSFET and IGBT Tech - Diff and similarities
 Required Drive Power Overcoming Power Switch Gate Charge

 Maximum Drive Current requirement
 Variable Output Voltage Swing Maximum Switching Frequency
 Maximum Operating Temperature Isolation Requirements
7

Before proceed with Gate Drivers we need to understand the diffbetween MOSFET and IGBT Although both IGBT and MOSFET are voltage-controlled devices, IGBT has BJT-like
conduction characteristics.
 Terminals of IGBT are known as Emitter, Collector and Gate, whereas MOSFET has
Gate, Source and Drain.
 IGBTs are better in handling higher power than MOSFETs.
 IGBT has PN junctions. MOSFET does not have these.
 IGBT has lower forward voltage drop compared to MOSFET.
 MOSFETs have higher switching frequencies and hence these are preferred over IGBTs
in power supplies like SMPS and small to Medium Motor Drivers

8Selecting the best Power Switch (IGBT vs. FET vs. Module)
DISCLAMER:
 IGBTs and HV MOSFETs are similar in many ways but differ from a performance and application
perspective
 A “one size fits all” approach does not work The best device is the one that best meets the application needs in terms of size, efficiency andAmps/$ capability..!

Power Switching Devices  When comparing MOSFET and IGBT structures look very similar The difference is the addition of a P substrate beneath the N substrate The IGBT technology is certainly best Switch to use where breakdown voltages above 1000 V While the MOSFET is certainly the device of choice for breakdown voltages below 700 V

9‘Power Switch’ - Fundamental Component in PowerElectronics

Ideal switch:
Blocking loss, POFF = VOFF x IOFF = 0
Conduction loss, PON = VON x ION = 0
4 quadrant operation

Power Switches control flow of current in power electronic circuits by
operating in 2 states (ON/OFF) GATE (G) terminal controls ON/OFF status of switch
 Modern Power Electronics dominated by Switch Mode Power conversion

The quick DIFFMOSFET’s:

IGBT’s:• Improved switching speeds.

• Improved production techniques, which has• Improved dynamic performance that
requires even less power from the driver.

• Improved durability to overloads• Lower gate-to-drain feedback capacitanceresulted in a lower cost

• Improved parallel current sharing• Faster and smoother turn-on/-off waveforms• Lower thermal impedance which, in turn,has enabled much better power dissipation• Lower rise and fall times, which has
allowed for operation at higher switchingfrequencies• Lower on-state and switching losses• Lower thermal impedance• Lower input capacitanceIGBT vs. MOSFET
Conditions based• Low Switching Frequency (<20kHz)• High Power levels (above say 3 kW)• High dv/dt needed to be handled by
the diode• High Efficiency is needed at Full load

• High Switching Frequency (>100kHz)• Wide line and load conditions• dv/dt on the diode is limited• High efficiency is needed in Light Load

MOSFET
Preferred

IGBT
Preferred
Application based• Motor Drives (>250W)• UPS and Welding H Bridge inverters• High power PFCs (>3kW)• High Power Solar/Wind Inverters(>5kW)

IGBT
Preferred12

20/01/2021• Motor Drives (<250W)• Universal input AC-DC Flyback
and forward converter power supplies• Low to Mid power PFCs (75W to 3 kW)• Solar Micro Inverters

MOSFET
Preferred

Basically all powerswitches need a gate
driver!
Gate Driver Functions:• Turn ON/OFF power switch• Amplify logic signals• Level shifting• Protection Functions

Power Switch Apps in a nutshell (Graph) Silicon MOSFET Low to mid-power applications
 Reached theoretical performance limit

 IGBT - Insulated Gate Bipolar Transistor
 Scaled for High voltage, high power Least expensive per watt at high power Slower but perfect for motor control

 SiC - Silicon Carbide (breakthrough) High voltage, high current, high temperature
 Faster switching requires gate drivers that
can tolerate high dV/dt

 GaN - Gallium Nitride (breakthrough) Low(er) voltage, high current
 Fastest switching (higher dV/dt)
 Narrow gate drive voltage range

MOSFET and IGBT need for Gate Drive primer
 IGBT & MOSFET is a voltage-controlled device used as a switching element inPower Switching Circuits

 The GATE is the electrically isolated control terminal for each device
 To operate a MOSFET/IGBT, typically a voltage has to be applied to the gate The structure of an IGBT & MOSFET is such that the gate forms a nonlinear
capacitor that can not change its Voltage instantaneously The minimum voltage when the gate capacitor is charged and the device canjust about conduct is the threshold voltage (VTH) When Higher Power IGBT/MOSFET is used, the higher Current is required toTurn ON/OFF Power Switch
 Gate Drivers are used to apply voltage and provide drive current to the gateof the power device
 Gate Drivers have fundamental parameters, such as timing, drive strength,
and isolation

How does GATE terminal of a Power Switch Work ?
 Let’s take example of a power MOSFETGATE terminal controls ON/OFF state of MOSFET VGS = Voltage Between Gate & Source
 To turn ON: Apply a positive voltage, VGS > Threshold level To turn OFF: VGS < Threshold level
 GATE is a capacitive input, highimpedance terminal 2 parasitic capacitors inside MOSFET
internal structure (CGS, CGD)

CGD

G

D

(Gate-to-Source Voltage) VGS
ON

ON

CGS

Threshold
OFF

OFF

S

Required Drive Power The Gate Driver serves to turn the power device on and off, respectively
 In order to do so, the gate driver charges the gate of the power device up to
its final turn-on voltage Vge(on), or the drive circuit discharges the gate
down to its final turn-off
voltage Vge(off) The transition between the two gate voltage levels requires a certain amountof power to be dissipated in the loop between gate driver, gate resistors andpower device
 Today, high-frequency converters for low and medium-power application are
predominantly making use of the gate voltage-controlled device such as
power metal-oxide-semiconductor field effect transistors (MOSFETs)
 For High Power Applications best devices in use today are Isolated Gate
Bipolar Transistors (IGBT’s) Gate Drivers are not just for MOSFET’s and IGBT’s but also for fairly new andesoteric devise from Wide Band Gap group such as Silicon Carbide (SiC) FET’sand Gallium Nitride (GaN) FET’s as well16

What is a Gate Driver It is a power amplifier that accepts a low-power input from a controller IC andproducesthe appropriate high-current gate drive for a powerMOSFET Gate Driver device applies voltage signal (VGS) between Gate (G) &Source (S) of power MOSFET, while providing a high-current pulse
 To charge/discharge CGS, CGD QUICKLY To switch ON/OFF power MOSFET QUICKLY

Gate Driver

Switch Turn-On

Gate Driver

Switch Turn-Off

Gate Drivers Markets + Application Topology
 Single & ½ Bridge
 AirCon, White goods
 Pump & Motor control
 Lighting
 Consumer electronics power
conversion.

 Full Bridge
 Low/mid voltage DC-AC power
 Inverters
 AC/AC & DC-DC converters,
 Motor control applications.

 3-Phase Small BLDC motors and AC motors
 Fluid or Air Pumps
 Uninterruptible power supply
 Solar inverters and other inverters
18

Drivers usage19

20/01/2021

Gate Drive Requirements and Considerations
 Total Gate Charge (Qg)
Generally higher for HV MOSFETs (larger die compared to IGBT, for same current rating) Turn on gate resistors
Generally higher values used for IGBT (lower input capacitance compared to HV MOSFETs
 CMTI – Common Mode Transient Immunity
Maximum tolerable rate of rise or fall of the common mode voltage applied between two isolated
circuits. The unit is normally in kV/us or V/ns. High CMTI means that the two isolated circuits,
both transmitter side and receiver side will function well within the Datasheet specs
 Gate Drive Voltage
Higher (15 V) preferred for IGBT, 10 V is ok for HV MOSFETs

 Negative Gate Drive Voltage
Generally not needed for HV MOSFETs, sometimes used for older process IGBTs and definite
need for SiC and GaN
 Gate Driver vs. IGBT/MOSFET consideration
Driver that can source/sink higher gate current for a longer time span produces lower switchingtime and, thus, lower switching power loss within the transistor it drives.
20

Gate Driver Selection Questions
 How many Inputs/Outputs required from the Gate Driver Required Voltage Rating

 Driver Current Rating
 Gate Charge
 Maximum Switching Frequency
 Variable Output Voltage Swing Maximum Operation Temp
 Special Functions
 Key External Component selection
 Isolation Requirement – Yes or No

Selection
 How many Inputs/Outputs are provided for/by Gate Driver For the inputs, It depends on the choice of the MCU and the control
algorithm chosen For 2 inputs, the choice is high side low side gate driver For 1 input, the choice is a half bridge driver Number of outputs depend on the number of half bridges that require
driving Voltage Rating Selection (Rule of Thumb) A conservative rule is to pick a voltage rating 3 times the operating
voltage, with 1.5 times being a recommended minimum However, thisdepends purely on the system requirements
 Gate drivers always work with MOSFET/IGBT, best practice is to matchthe voltage rating of the chosen MOSFET/IGBTGate Drive Current Need

 How much drive current is required Information about the required gate charge to raise the gate voltage tothe desired level is essential
 Gate charge information is provided by the MOSFET manufacturer in theirdatasheet, usually for a gate voltage of 10 V
 Now that we know the required gate charge, we choose the drive current
rating depending on the rise and fall times we are targeting.
 The equation to use is Qg = Igate * time Example: Qg = 50nc. Required Tr = 50ns and Tf = 25ns.
 Igate (source) = 50/50 = 1A of source Igate (sink) = 50/25 = 2A of sink

 The above calculation provides us with a minimum figure. Often it is noteasy to find a tailored gate driver. Best practice is to choose a gate driverwith higher than the required rating and use series gate resistors to limit
the source and sink currents

Gate Driver Special Functions
 Special Functions
 Some applications need special functions like
 inbuilt and/or adjustable dead time enable option
 shoot through prevention logic
 delay matching etc. to ensure the selected gate driver comes withthe required optional features

 Key external component selection
 Boot-strap Capacitor Selection
 Gate Resistor Selection
 Layout Recommendations

24External Devices Selection
 Gate Resistor Selection
 A typical gate drive current control circuit needs Series
Resistor with Device Gate and Optional Reverse biased
Diode.
 By adjusting the Tonn and Toff resistors respectively,
the rise and fall times can be controlled individually Reverse Biased Diode will facilitate Toff if need be Capacitor Selection
 The capacitance of the bootstrap capacitor should be highenough to provide the charge required by the gate of thehigh side MOSFET. As a general guideline, it is recommended
to make sure the charge stored by the bootstrap capacitor isabout 50 times more than the required gate charge at
operating V CC (usually about 10V to 12V)
 The formula to calculate the charge in C BS to provide
sufficient gate charge as follows; Q = C * V,
where Q is the gate charge required by the external
MOSFET. C is the bootstrap capacitance and V is thebootstrap voltage Vbs

Gate Driver Category Definition
Junction Isolated

Non-isolated

Single - Channel

Multiple - ChannelHigh - Side

Non-isolated• Single or multiple channel• Cheapest, simple solution for many
applications where only a low-side driver isneededHigh/Low

Half-Bridge

Galvanic Isolated

Three-Phase

Junction Isolated

1-Channel

2-Channel

Galvanic Isolated• High Side, High/Low and Half Bridge• Floating HV well
• From LV to 1200V breakdown voltage• Normally needed in very highpower/high voltage systems.
• Three options: Optical,
Inductive, Capacitive

Applications• Automotive• Industrial Systems• Consumer Devices• Appliances• Consumer Devices & Power Tools• Auxiliary Automotive & Motors Drives• Offline Power• Automotive traction inverters• Industrial Drive• Server Rack Power• Solar and Energy Storage

Products
FAN3100/11
FAN3181
FAN312x
NCD5700/1/2/3
26

FAN321xFAN322x20/01/2021

FAN73611

FAN8811
FAN7392
NCP51530
NCP5183

FAN7382
FAN73833
FAN73912
NCP5106B

FAN7382
FAN73833
FAN73912
NCP5106B

NCD57000/1
NCP5708x
NCP51157

NCD57252
NCP51561

Gate Driver Considerations
PURPOSEEFFECT

CONCERNS

Keep PWR Switch in
ON state

Minimize ON state
Voltage and reduce
conduction losses

Gate Voltage/Under
Voltage Lockout

Keep PWR Switch in
OFF state

Minimize leakage current
and prevent spurious turn
ON/OFF due to EXT or INT
disturbances

Gate Voltage/Under
Voltage Lockout

Drive SW from ON to
OFF and OFF to ON

Minimize SW losses &improve EMI/EMC

Noise Immunity

Endure large GND loops &potential differences withhigh energy present

Separate Signal PWR
GND/Reinforced

OCP, OTP, Shoot through,UVLO protection

Miller Capacitance
Clamp/Soft Shutdown

SW Protection
27

Peak Source/Sinkcurrents

Isolated Gate Drivers – Why, What and How Motivation in PowerManagement drivers to Isolation
 Rising concern for environmental issues and energy savings is driving growth in theuse of dynamic power control and inverters throughout the industrial, power, andhome appliance markets
 In the U.S., Asia and Europe, the use of general-purpose inverters, DC Motors and BLDC
Motors and AC servos is expanding rapidly, especially in the up and coming markets
 Most important is there has also been steady growth in the use of these devices in
power-related fields like wind and solar generation, two markets that are expected to
grow well into the future Pricing on MCU has dropped dramatically and current use of such Devices to control
almost everything has proliferated into every aspect of Life, even Power Management IN order to separate High Voltage/Power from Logic Level Galvanic Isolation is a MUSTHAVE and World Governments mandate soIntroduction to Isolation
Galvanic isolation is a principle ofisolating functional sectionsof electrical systems to prevent
current flow.

Reasons for Galvanic Isolation
 Safety of End User
 Protecting LV circuits from HV Circuits
 Filtering of Common-Mode Noise Eliminating Ground Loop Noise

Circuit A

Galvanic Isolation

 Level-Shift between Power Domains

Circuit B• Optically Isolated Devices

High Impedance
GND A

29

Technologies used for Galvanic Isolation

GND B• Digitally Isolated Devices• Insulation with on-chip capacitors• Insulation with on-chip inductors• Insulation with off-chip capacitors

Why isolate, Summary?
 To protect from and safely withstand high voltagesurgesthat would damage equipment or harm humans
 To protect expensive controllers – intelligent systems
 To tolerate large ground potential differences anddisruptive ground loops in circuits that have high energy
or are separated by large distance To communicate reliably with high side components inhigh-voltage high performance solutions
30

When Isolation is necessary and How to Isolate
 Isolation is need it when there is more than One Conductive Path between
two circuits creates a Ground-Loop Multiple Ground Paths can lead to unintended compensation currents
 Ground Loops can be broken by:
 Disconnecting the Grounds
 Common Mode Chokes
 Frequency Selective Grounding (Modified Tank Circuits) Differential Amplifiers
 Galvanic Isolators

 ONLY TRUE GALVANIC ISOLATION PROVIDES PROTECTION FOR VERYLARGE POTENTIAL DIFFERENCES

31

Galvanic Isolation –Reason and Methods
 ISOLATION – Means of transporting data and Power between High
Voltage and a Low Voltage Circuit while preventing
 Hazardous DC, AC or Uncontrolled Transient currents flowing between two circuits
 To protect from and safely withstand high voltage surges that would damage equipment or harm
humans To protect expensive controllers – intelligent systems
 To tolerate large ground potential differences and disruptive ground loops in circuits that have highenergy or are separated by large distance To communicate reliably with high side components in high-voltage high performance solutions

32

Isolation Market & Technologies
Optocouplers

Digital Isolators (DI)Digi-Max™ (DM)Technology
Optical: LED + Photodiode

Digital: On-Chip

Digital: Off-chip with Ceramic Insulator

Benefits
Lowest Cost
EMI / EMC Immunity
Isolation Reliability / Safety

Low Cost
Stable over Temp & Time

EMI / EMC Immunity
Isolation Reliability / Safety
Stable over Temp & TimePrimary Markets
Power Supplies
Industrial HP Drives

Automotive (EV/HEV)
Telecom

Industrial HP Drives

Lead Suppliers

Unique to33

1/20/2021

What is the Popular Isolation methods in gate driver ?
 A) Optocoupler Signal transfer between two isolated circuits
using light – LED + phototransistor, 1970s ~(ON Semi, Avago, Toshiba and others) B) Transformer
 Integrated micro-transformer and electronic
circuitry, 2001 and on…
 C) Capacitor
 Signal transmission through capacitive
isolation with On- Off-Keying (OOK)
modulation, 2007 and on…

3

Common Isolation Techniques and Main Issues
Optical -> Optical transmission (fiber optics), optical coupling (optocoupler)• LED degradation over time/temperature
Emitter Chip
Epoxy
• Slow (<25Mbit/s)
Outer Mold
Input
• Not economical for high-channel countLeadframe

Capacitive (on-chip/off-chip)• Thin insulation barrier (on-chip)• Insulating materials susceptible todamage from EOS/ESD (on-chip)• Higher power consumption (off-chip)• EMI/EMC challenges
Magnetic -> Coreless transformer, magneto resistive, hall effect• Magnetic interference• EMI susceptibility• Thin insulation barrier
35

35

Reflector

Detector Chip
IR Transparent
Material
OutputLeadframe

THE importance of Integration of Driver + Isolation in single package
Adding isolation is becoming mandatory as part of regulatorycompliance System solutions becoming smaller in size

Telecom bay stations and RRUs – Higher data transactions
Datacenters – space limited – but more storage Higher efficiency

Switching to higher voltages
More intelligence to systems
More protection of controls

 Higher performance density
 Isolation robustness
 Availability of high voltage devices
Wide band gap devices – SiC, GaN

Levels of Isolation
 Functional Isolation
 Functional Isolation is necessary for the proper operation of a product. There is noneed for protection against electric shock Basic Isolation
 Basic Isolation is single level of isolation providing basic protection against electricshock Reinforced Isolation
 A single insulation system that provide electrical shock protection equal to double
insulation
 Supplementary Isolation
 Double Isolation

Comparison of Isolation Techniques
Attribute

Opto-Coupler

On-chip Magnetic

On-chip Capacitive

Digi-Max™
Off-chip Capacitive

Isolation Materials

Epoxy/Silicone gel

Polyimide

SiO2 or equivalent

Ceramic Substrate/ Epoxy

Signal Coupling

Optical (LED +diode)

Magnetic field

Electric field

Electric field

Performance Across Temp & Time

VariesConsistentConsistentConsistentLife Expectancy~10 Yrs~ 20 Yrs~ 20 Years~20 Years

Speed

Slow

Fast

Fast

Fast

> 400 µm

~20 µm~20 µm> 500 µm

Yes

No

No

Yes

~25 kV/µs> 100 kV/µs> 100 kV/µs> 100 kV/µs

Non-issue – too slow

Design techniques

Signal level dependent

Signal level dependentNon-issue (light transmission)

Design techniques

Design techniques

Design techniques

Junction Temperature

Up to 125°C

Wide range (150 °C)

Wide range (150 °C)

Wide range (150 °C)

Standards

UL1577
IEC60747-5-5

UL1577
VDE0884-11

UL1577
VDE0884-11

UL1577
VDE0884-11

No modulation required

On-Off Keying

On-Off Keying

On-Off Keying

Limited

Yes

Yes

Yes

Distance Through Insulation (DTI)
Meets EN60950 >0.4mm DTI
Common Mode Transient Immunity(CMTI)EMI
EMC

Susceptibility
Radiation

Modulation Method for Internal
Signal Xfer
AEC Qualified Portfolio
38

Working Principles of Bi-Directional Ceramic Isolator• Bi-Directional communication between two isolated circuits.
• Off−chip ceramic capacitors that serve both as the isolation barrier and as the medium of transmission for
signal switching using on−off keying (OOK) technique,• Tx, modulates the VIN input logic state with a high frequency carrier signal.
• Rx detects the barrier signal and demodulates it using an envelope detection technique.

39Digi-Max™ Family of Hi-Speed Digital Logic-to-Logic Isolators
Available in Industrial (NCID) and Automotive Grade (NCIV)
NCIV9211

NCIV9200

NCIV9600

NCIV9420
VDD1

VDD2

GND1

GND2

NC

NC

NC

IN1

EN2

IN2

IN1

IN3

OUT2

OUT4

NC

NC

NC

NC

GND1

GND2

GND1

GND2

OUT1
IN2

NCIV9311

NCIV9210

NCIV9410

NC

NC

GND1

VDD1

IN1

IN1

IN2

OUT2

OUT3

NC

NC

GND1

NC

EN1

EN2

NC

NC

NC

GND2

GND1

GND2

GND1

GND2

IN2
NC

Released

OUT2
OUT3
IN4

NCIV9630

VDD2

VDD1

VDD2

VDD1

VDD2

GND2

NC

NC

IN A

OUT A

OUT1

IN1

OUT1

IN B

OUT2

IN2

IN3

IN3

NC

OUT4

GALVANIC ISOLATIONOUT1GALVANIC ISOLATIONGND2GALVANIC ISOLATION

GND1

VDD1

OUT1

NCIV9510

VDD1

OUT2
OUT3
IN4

IN C
IN D
NC

GALVANIC ISOLATIONEN1GALVANIC ISOLATIONVDD2GALVANIC ISOLATION

VDD1

NC

SO-16 WB
Package

NCIV9400

OUT B
OUT C
OUT D
NC

Out E

In E

GND1

GND2

2020

Other Configurations Available

2021

ON-CHIP ISOLATION -Micro-transformers and capacitive coupling• A digital isolator (also known as on-chip isolators) is used to get a digital signal across a galvanic isolation
boundary.
• They serve a similar purpose as optocouplers, except optocouplers are far too slow and error prone for highspeed (>1MHz) digital signals.

• Two principal technologies are being used for digital isolators: micro-transformers and capacitive coupling.
• In both cases, an insulating material separates both the primary and secondary side, such material being a polyimide (PI) ora silicon dioxide (SiO2) layer.

Temperatures up to125°C

While SiO2 is

12

CORELESS TRANSFORMERS
Also called micro-transformers• Coreless Transformers or Coreless Planar Transformers (CPT) were first developed as a solution for insulating
the high voltage power circuit from the low voltage control circuit allowing integration on-chip.
• The coreless transformer technology has been chosen by main major driver IC manufacturers as the mostadequate solution among on-chip isolation technologies.
• This Tech has several design advantages:• While a discrete transformer needs a core to direct the magnetic flux, the coils in an IC can be placed close enough to save thecore.
• The design of these transformers gives the designer greater control in optimizing, such as precise winding spacing andorientation when compared to traditional wire-wound magnetics.
• Greater stability over high temperatures. Pulse transformers suffer from magnetic property changes and accelerated aging.
• The pulse response of a planar transformer is typically less than 2ns, while the propagation delay is about 20ns. For optocouplers,
the propagation delay is around 500ns.

• For signal transfer, the input data is usually encoded before being transmitted to the primary data transformer. A decode is used at
the secondary side to recover the signal.
• Isolation between the input and output is provided by the insulation layers between the primary coil and the secondarycoil.

Isolation Technologies (Capacitive)

Figure 4

Advantages:• Physical barrier utilizing dielectric insulating material• No LED to wear out• Total immunity to magnetic fields• Used by Texas Instruments (developed by Burr Brown)
Disadvantages:• Higher current consumption than transformer isolation

Figure 5

Honorable mention - Isolation Technologies (RF)This RF ISO tech is usedby Silicon Labs

Advantages:• Requires less input power than optoisolator
technologies• Lower propagation delay than optoisolators• Total immunity to magnetic fields• No LED to wear out
Disadvantages:• Higher current consumption than magnetic isolation• Carrier frequency limits pulse position accuracy

ISOLATION TECHNOLOGY PER POWER• Optocouplers and pulse transformers have been the most used technologies to provide the galvanic
isolation for gate drivers.

• Fiber optic remains a high-end solution, for high power applications, such as rail traction, wind turbines or
the grid.
• But since a couple of years, chip integrated isolation technologies, such as coreless transformers areattacking the traditional optocoupler & pulse transformer markets.

Chip
integrated
isolationtechnologie
s arepenetratingthe
traditional
optocouplerandtransformer
market.

Device voltage

Comparison between MOSFET and IGBT Isolated drivers
Power Switch

MOSFET

IGBT

Switching frequencies

High (>20 kHz)Low to Medium (5-20kHz)# Channels

Single and Dual

SingleProtectionNo

Yes – Desaturation, MillerClamping

Max Vdd (power supply)

20V

30V

Vdd range

0-20V-10 to 20V

Operating Vdd

10-12V

12-15V

UVLO

8V

12V

CMTI

50-100V/ns<50V/ns

Propagation delay

Smaller the better (<50ns)

High (not critical)

Rail Voltage

Up to 650V

>650V

Typical Applications

Power supplies – Server, datacom, telecom,
factory automation, onboard and offboard
chargers, solar u-invertersand string
inverters (<3kW), 400-12V DCDC - Auto

Moto drives (AC machines), UPS, Solarcentral and string power inverters(>3kW), Traction inverters for auto

Comparison of SiC to MOSFET and IGBT iso drivers

Green font highlights
similarities

Power Switch MOSFET

IGBT

SiC

Switchingfrequencies# Channels

High (>20 kHz)Low to Medium (5-20kHz)

High (>50 kHz)Single and Dual

SingleSingle and Dual

ProtectionNo

Yes – Desaturation, Miller Clamping

Yes – Current sense, Miller Clamping

Max Vdd (power
supply)

20V

30V

30V

Vdd range

0-20V-10 to 20V-5 to 25V

Operating Vdd

10-12V

12-15V

15-18V

UVLO

8V

12V

12-15V

CMTI

50-100V/ns<50V/ns>100V/ns

Propagation delay

Smaller the better (<50ns)

High (not critical)

Smaller the better (<50ns)

Rail Voltage

Up to 650V

>650V

>650V

Moto drives (AC machines), UPS,
Solar central and string power
inverters (>3kW), Traction
inverters for auto

PFC – Power supplies, Solar inverters,
DCDC for EV/HEV and traction inverters
for EV,
Motor drives, Railways

Typical Applications Power supplies – Server, datacom,
telecom, factory automation, onboard
and offboard chargers, solar u-inverters
and string inverters (<3kW), 400-12V
DCDC - Auto

Gate Driver Isolation Requirements in Motor Drivers

A conceptual power drive system block diagram
Electronic devices and integrated circuits (ICs) used
for isolation are called isolators
Isolator

Sensing elementwith Isolation

Power Supply application
Rectified A C

Primary

385V 400V
BoostedDC
OutputA C Line:
85-265 VAC

Distribution
B U S Voltage(48, 24,
12V)

Main
Card
Power
3.3V

Secondary3 .3 V2 .5 VPFC

DownS tre a m
DC/DC

Local
D C /D C

MOSFET
Drivers

1 .x V

Isol atedFeedback

Local
D C /D C

S yn c h.
Buck
DriverThere is high voltage involved on the primary side of DCDC
PFC
Boost
Reduces HarmonicContent, lowers peak current andmakes load look Resistive

PWM

Local POL
Regulators

PWM is main loop to regulate
Vo, provides proper duty cycle

PWM is main loop to regulate
Vo, provides proper duty cycle

Server / Telecom Power Supply example
AC85~265V#nPFC
EMI Filter#2 ction)(Power Factor Corre

48V

DC-DC #n

400VDC

DC-DC #mPFC
#1 ion)(Power Factor Correct
PFC

DC-DC

Bus Converters

POLs

Batteries#1(Power Factor Correction)

POL s

…

12V

uProcessor, Memory, HDD…
All pictures are Used under Fair use, 2015

VDC-Link 400V

Lkp
CB

48V

48V
Lk
9.6V/12V

CR
Lm

1. 1Ch/2Ch low side driver
2. High and low side driver
100V
600V

Lks
Lks

12V

Motor driveapplication
Gate driver options:- 6 single channel iso
drivers with noprotection ( 8pin) andusually reinforced- 6 single channel iso
drivers with protection(DESAT, Miller clamp or
split output) (16 pin)
- 3 single channel iso
drivers
for high side only (8 or
16 pin) along with 3
non isolated drivers

Solar micro (300W)/string (<3kW) inverter

Usually MOSFET single
inverters needing isolated(basic or reinforced) drivers

Isolation – OPTO vs. Digital
Key Article

EffectDigital Isolators

Optocoupler

Timing performance

Enables higher throughput and efficiency for end productLow propagation delay and skew, better
part to part matching

High propagation delays and skew, worse part topart matching

Parasitic capacitive coupling

The lower the parasitics, the higher the CMTI

Less than half the parasitic coupling of
optocouplers

High parasitic coupling with interdependent
parameters

Reliability and high temperature
operation

Longer product lifetimes

No wear out mechanisms, 60+ year
operating lifetime at 125 °C at maximum
VDD

Intrinsic wear-out mechanisms; 10x lower lifetime

Input current

High input current means higher power consumption

CMOS input buffers need very low input
current

Requires higher input current to be competitive

Ease-of-use

Minimum external BOM needed to extract fullfunctionality and performance

Fewer second order effects, minimum
BOM required for full performance
guarantee

Significant first and second order effects,
temperature dependencies, imprecise current
thresholds, CTR require external BOM to get stableperformanceElectro-magnetic immunity andradiation

Immunity provides robustness and low radiation implies
low noise generation

Capacitive-coupled devices arecomparable to optos while magneticallycoupled devices can be noisy and aresusceptible to external EM noise

Opto are generally highly immune and have low
radiation

Safety compliance

Ensures safety standards are tested and certified

54

20/01/2021

General trend is new-generation isolators Opto have traditionally been used for many years
are on par with opto
and are compliant

Active Standards Organizations: Keep Up-to-Date With Rapidly Evolving Requirements

IEC 60747-5-5

IEC 60747-17

Optoelectronic devices

Magnetic and capacitive
coupler for basic andreinforced isolation
Valid from ~ 2018 Target

photo-couplers

VDE 0884-10 and 0881-11
Magnetic and capacitive couplers
for safe isolation
Will be replaced by VDE 0884-17

Component level standards(component insulation capabilities)

VDE 0884-17
Magnetic and capacitive
coupler for basic andreinforced isolation
Valid from ~ 2018 Target

System level standards (isolation coordination)

IEC 60664-1

IEC 61800-5-1 new UL 61800-5-1

Insulation coordination for equipment within low-voltage
systems - principles, requirements and tests

Adjustable speed electrical power drive systems –safety requirements

Key requirements for an isolated driver
In addition to understanding the levels of isolation.... It is important to find out about the driverfunctionalities:

 Propagation delay

 Common Mode Transient Immunity (CMTI)
 Rise time/fall time Maximum driver side supply voltage
 UVLO Channel to channel delay Protection schemes Dead time control and overlap
 Enable/disable features

Gate Driver Topologies
Non-isolated

Signal Isolated

Junction Isolated

Galvanic Isolated

VDD

VDD

VDD

VCC

Isolation

Gate Driver

Galvanic Isolated
Gate Driver
MCU

MCU

Junction
Isolated Gate
DriverMCU

Galvanic Isolated
Gate Driver
Isolation

•
•
•
•
•

Very simple
Minimal features
Layout critical to prevent crosstalkand GND currents
May need extra Cap & Common
Mode Choke to decouple noise
APPS – Low Power SMPS with Low
Cost MCU; Low drive Power57

20/01/2021

•
•
•
•
•

Gate Driver

Not commonly used
Layout can be complex due to extra IC’s
Decoupling Caps extra cost
GND noise Common Mode choke could
be required
APPS – Low to Med Power; Afterthought
Isolation need it if long cables are used

•
•
•
•
•

Low Cost
Easy layout
Need to select Boost Diode and Cap withcare for speed/noise ratio
Possible Cap needed for cross - coupling
reduction due to NO galvanic Isolation
APPS – DC-DC; PFC; Small-Med Motordrivers; Consumer Appliances; Med Power
UPS< 3KW

•
•
•
•
•

IC is complex; all Integrated
Full protection features
Higher cost/Highest safety
Ease of Layout, no extra
components
APPS – High Power AC/BLDC
Motors; Industrial SMPS; Solar
Inverters; High Power UPS > 3KW

Isolation Tech: OPTO, Fiber-optic & Level Shift Pros – Cons
OPTO-Coupler
Pluses:SimpleBeen around longest
High Iso Capacity up to 1 KV
Drive Speed up to 1 MHz
Offers good response at Lower Fsw
Very inexpensive

Minuses:LED Degradation
Power supply required
Slow Prop DelaySlow Rise/Fall times
Frequency Response is slow
No energy Transmission

Fiber Optics

Pluses:Unlimited Isolation Voltage
Fast Response time
Distance between points isunlimitedGreat Communication
between Points
Minuses:ExpensivePower Supply requiredNo Energy Transmission

Level Shit/Junction
Isolation
Pluses:High Current Capability
Precision Analog Circuitry
Voltage levels of 1200 V/600
V/500V/200 V & 100 V
Configuration of 3-Phase/Half
Bridge/Single Channel &moreBest Price/Performance ratio
Minuses:No Galvanic Isolation
Power Supply requiredNo Energy Transmission

Isolation Tech: Inductive Coupling and Capacitive Pros – Cons
Transformer, IronCore

Planar Core

Coreless IC

Pluses:Galvanically Isolated
Reinforced Isolation for
1700V MIN
Fast & Accurate, lowjitter/low delay
Flexible Form Factor
Low coupling CapacitanceBi-Directional

Pluses:Unlimited Isolation
VoltageFast Response time
Distance between
points is unlimited
Great Communication
between Points

Pluses:High Current
Capability
Low Cost
Very Fast
Low coupling
Capacitance

Minuses:Expensive
10% Turn ON/OFF stability
issuesSingle Source
Limited Product Portfolio, yet

Minuses:ExpensivePower Supply
requiredNo Energy
Transmission

Minuses:Single SourcePower Supply
requiredNo Energy
Transmission

Capacitive
Isolation

Pluses:Low Power Consumption
1700V MIN
Fast & Accurate, lowjitter/low delayPhysical Barrier with IsoMaterial
Minuses:Expensive
High Current consumption

ISOLATION TECHNOLOGY COMPARISON

Optocouplers
Fiber optic

Monolithic level
shifter
Pulse
transformer

Integrationlevel

Independent
power supply
needed at thesecondary>400nsMediumYes

Aging
issues$>100kV’s/µs

Negligible

MediumYes

Goodreliability

$$$$

None

50kV/µs-

Integrated
on the IC

No

-

$

Several kV>50kV/µs<100 ns

Bulky

No

Reliable$~20 nsIntegrated
on-chip ordriver IC
package

Yes

Very reliable$$

Isolation

Dv/dt
immunity

Few kV>50kV/µs

Several10’s kV

Propagatio
n delay

Digital isolation

Several kV>100kV/µs

Reliability(over time &harshenvironment)

Cost

Comparison between Gate Drive Transformer & High & Low
Side Driver with isolator
TProp
Bias PowerCIO
Parasitics
OvershootSizeType A

Type B

≈20ns
NO
≥10pF
Large (LLK)
Large
Bulky

≈100nsYes≤1pF
Very small
Small
Small

Isolation Evolution and Key Reasons behind it
THE need for Gate Driver change

Fasterswitchingfrequency

This causeeffectscenario isnow
principally
applied by
Wide BandGap
devices.

Highertemp.
inside thepowermoduleNeed forlower strayinductance

Need foron-chip
integrated
isolation

Driver IC
closer to
gate

Integrationof driverICs intransistor
package8

Construction of an isolated gate driver
Multichip module
Block
Diagram

Transmitter

Isolator

Receiver+ DriverApp
Schematic

NCD57000 - Isolated DriverPower Switch Impact on Gate Driver Evolution
Yet even higher working voltage
Faster DSAT detection
Higher CMTI
Enhanced safety features

Yet even higher
CMTI Narrow gate
drive window

Higher working voltage
Miller Clamp
DSAT detection

10 kW

10 kW IGBT Heat Sink

SiC Heat Sink

State-of-the-art Power Semiconductors (Wide Band Gap)
Si-MOSFET

IGBT

SiC-MOSFET

GaN

Nom-ON

Voltage Ratings
Optimal VGS
Max.Limit
Si-MOSFET≥650V-10~15V(-10~20V)

20~650V
0~15V(±20V)
10V

IGBT

12V

≥650V
-5~20V(-5~25V)

Nom-OFF≤650V-5~10V-4~6V(±18V) (-10~7V)

SiC-MOSFET

GaN
20V
18V
16V

5V
4V

3V

2V
- I-V curves are from datasheets of Infineon, CREE, EPC

Value of Silicon carbide in high voltage & high power
applications
 High power density – 10x more thanSilicon
 High current density
 High breakdown voltage
 Drive higher current in a reduced footprint High thermal conductivity
 High mobility – ability to switch at high frequencies

Trending towards integration: Isolated gate driver
TYPE A
Type A

FAN3224/NCP810
71
GA3550-BL

TYPE C: ISO Driver

PCB Area
Reduction – 76%(NCD57252 &NCP51561)

1.75

Area
(mm2)
31

Vol
(mm3)
54.25

10

420

4200

SUM

451

4254

2.65
1.75
2.4

111.3
54.25
49.41

295
95
119

SUM

215

509

W (mm)L (mm)H (mm)

5

6.2

17.4

24.13

TYPE B
Type B

ISO7520C
UCC27714
MURS360

10.5
8.75
8.1

10.6
6.2
6.1

 CMTI>100V/ns

 5kVrms reinforced
isolation
 TProp: 35ns Typ.

 Match./ TPWD < 5ns

110mm2

Gate Driver Key attributes
Negative Input/Output
Voltage Capability

Negative Voltage result from parasitic inductances caused by switching transitions, leakage oreven layout issues. Gate Driver ability to survive NEG Voltage is critical for robust, reliable
solution. High Immunity to GND noise

Propagation Delay

Supports higher Frequencies, reduction in reverse recovery losses. FET needs quicker switching
than IGBT and Fast Prop-Delay enables that, minimizing conduction losses in process

Delay Matching

IF FET’s used in parallel then it will support Drive with MIN delay differences. Reduces issues
with paralleling FET’s and easily doubles Current drive output for large FET’s

Wide VDD Range

Capability of using the same Gate Driver when diff Voltages are present as well as diff Power
Switches (MOSFET/IGBT). Also great in low- quality PS environment. Also support Split Railsystem where POS and NEG voltage present; IGBT /SiC FET’s

Operating Temp Range

Very consistent performance and robustness under Extreme Temp conditions (-40 Deg C – 125
Deg C)

68

3-Phase Motor Control (Industrial Robotics / Etc…)
Isolation
Boundary

VAVBVC
Industrial
comms(position /speed / torquereference)

Position
Loop

Speed LoopPWM unit

Torque /current loop
[FOC]

NCID9210
NCID9210
NCV57252 x3

Current
Feedback

IAIBICVDC

ΣΔInterface

OpAmp

DigitalIsolator
Angle

69

Speed

Angle

Angle
Feedback

Position
Feedback

Angle
Angle
SensorSensorAngle
SensorSpeed
Feedback

3-Phase Motor Control (Auto / Industrial Robotics / Etc…)
Isolation
Boundary

VAVBVC
Industrial
comms(position /speed / torquereference)

Position
Loop

Speed LoopPWM unit

Torque /current loop
[FOC]

NCID9210
NCID9210
DigitalIsolator

Gate
DriverCurrent
Feedback

IAIBICVDC

ΣΔInterface

OpAmp

DigitalIsolator
Angle

70

Speed

Angle

Angle
Feedback

Position
Feedback

Angle
Angle
SensorSensorAngle
SensorSpeed
Feedback

3-Phase Motor Control (Auto / Industrial Robotics / Etc…)
Isolation
Boundary

VAVBVC
Industrial
comms(position /speed / torquereference)

Position
Loop

Speed LoopPWM unit

Torque /current loop
[FOC]

NCID9210
NCID9210
Digitally Isolated
Gated Drivers

Current
Feedback

IAIBICVDC

ΣΔInterface

OpAmp

DigitalIsolator
Angle

71

Speed

Angle

Angle
Feedback

Position
Feedback

Angle
Angle
SensorSensorAngle
SensorSpeed
Feedback

Network Communications

Industrial Communication (PLC)
1-Ch
Optocoupler Digi-Max™

4x=

Optocoupler

Opto
coupler

Optocoupler
Optocoupler
Optocoupler

Digi-Max™
2-Ch
Optocoupler

2X
DigitalIsolator

DigitalIsolator

DigitalIsolator

72=

Automotive Electrification – PTC Heaters
15V
LDO
5V
LDO

Iso
Flyback

Isolated
Gate Driver

15V
LDO

15V
LDO

DigitalDigitalIsolator
Isolator

PSU
MonitorDigitalIsolator

Micro

CAN
Transceiver

Temp
Sensor73

Temp
SensorNon-Isolated
Gate DriverIndustrial Washing Machine

Industrial Communication (PLC)

Optocoupler

74

TRIAC
Optocoupler

Isolated
Gate Driver(Optical or Digital)

Analog Input Modules
Isolation
Boundary

DigitalIsolator

Mux

GPIO

Processor

Shift
Register

AnalogInputs75

Analog Mux

Precision
OpAmp

ADC

DigitalIsolator

SPI BusPower Supply

Isolation
Boundary

AC In

Input
BridgeRectifierPower
FactorCorrection

OutputRectifier /Sync
Rectifier

Voltage
Regulator

Optocoupler

76

Voltage
Regulator

OutputRectifier /Sync
Rectifier

DC OutThank you very much for your attention

77