Neel SeshanMarketing ManagerIsolationTexas Instruments
Steven MappusApplications EngineerHigh Voltage PowerTexas Instruments
High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
2 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
The high voltages present in factory automation,
motor drives, grid infrastructure and electric vehicles
(EVs) can be several hundred or even thousands of
volts – good for efficiency, but potentially harmful for
low-voltage circuits and humans.
The first priority of any system operating with
high voltage present is protecting maintenance
personnel and end-equipment users. The second
priority is establishing reliable and safe operation
between high- and low-voltage circuits, performing
such functions as voltage and current sensing,
power-supply control, digital communication and
signal processing. Galvanic isolation satisfies
both priorities by isolating the high voltage from
low-voltage sections.
What is galvanic isolation?Galvanic isolation separates an electrical system
in such a way to prevent the flow of DC and
undesirable AC between two partitions, while
still allowing signal and power transfer. Figure 1
on the following page illustrates two galvanically
isolated circuits.
When GND1 is broken from GND2, I1 is galvanically
isolated from I2. Since there is no commonality
between GND1 and GND2, there is no common DC
GND current shared through the isolation barrier. In
addition to isolating shared GND connections and
signal communication without conduction, it is also
possible to use galvanic isolation for voltage-level
shifting, since GND2 is transferable to a different
floating potential relative to GND1.
High-voltage systems require more consideration
around isolation because more bidirectional signal
information is communicated across the barrier.
Many analog and digital circuits call for specific
This paper examines isolation requirements
for electrical systems and how high-voltage
semiconductors can help designers meet
their isolation needs.
At a glance
What is galvanic isolation?
Galvanic isolation prevents current
from flowing between different voltage
domains of a system. The primary
motivation to isolate is driven by
protecting personnel and equipment
and complying with industry standards.
Understanding isolation technologies
Optical, capacitive and magnetic tech-
nologies are common for transferring
power and signals across an isolation
barrier. Each approach varies with
regards to material composition, speed,
reliability, and isolation voltage ratings.
TI isolation technologies
Texas Instruments’ (TI’s) advancements
in capacitive and magnetic isolation
technologies transfer power and high-
speed signals safely and reliably across
the isolation barrier.
1
2
3
3 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
bias voltage requirements where both digital signals
and power cross the isolation barrier. An isolated
high-resolution analog-to-digital converter (ADC)
may require 3.3 V in the same system, whereas an
isolated gate driver may require +15 V and –5 V.
Figure 2 shows a variety of signal types and bias
power crossing the isolation barrier: 3.3-V or 5-V
low-voltage pulse-width modulated (PWM) signals
pass from the microcontroller (MCU) to the isolated
gate drivers, which in turn require +15 V and –5 V
bias derived from the 24-V system power bus.
Isolated feedback signals indicating phase, voltage
and position must cross the barrier reliably from
the 1.2-kV high-voltage side into the low-voltage
partition for closed-loop motor control.
Maintaining the integrity of the isolation boundary
protects personnel and equipment while simul-
taneously reducing expensive downtime. Several
methods of isolation implementation exist, each
with its own pros and cons. To achieve the optimal
level of isolation performance, it’s a good idea to
understand each method.
Figure 1. Low- to high-voltage galvanic signal isolation.
VDD1 VDD2 HV
I2I1
Input
Nocurrent
Output
Galv
anic
isola
tion
Load
GND1 GND2 GND2VCM
Power
Figure 2. Block diagram of an AC motor drive.
Position feedback
Communicationinterface
24-V DC system power bus100-V to 1200-V line power
Communication
AC/DC
Off-line power supply
(optional)
IndustrialEthernet
PHY
IndustrialEthernet
PHY
Industrial485 PHY
Industrial485 PHY
IndustrialCAN PHY
IndustrialCAN PHY
Control(with Fieldbusintegration)
Ext ADCrequired whenintegrated ADCnot presentor high-performance(high-endmotor control)
Motor drive
ControlMCU
InternalADCs
PRU
VREF
SARADC
SafetyMCU
MCU
PROT
DC/DCconverters & LDOs
IsolatedDC/DC
Power stage
Phase/voltagefeedback (options)
OPA Sensors
SDM
IGBTs
Encoder
Isolatedgate drivers
AMP
Isolatedanalog/
digital IO
Isolateddigital IO
OPA
4 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
High-voltage isolation concernsFunctional, basic and reinforced isolation refer to
the insulator rating level assigned to an electrical
system, as listed in Table 1.
Functional isolation refers to the minimum amount of
isolation assigned to a system so that it will function
properly, without necessarily protecting against
electric shock. One example of functional isolation is
proper printed circuit board conductor spacing for a
given voltage rating.
Basic isolation provides “sufficient” protection
against electric shock, with a safety rating at
parity with the highest system-level voltage.
An example of basic isolation is the addition of
insulating barrier tape between polyimide-coated
transformer windings.
Reinforced isolation is the highest commercial
rating applied to high-voltage systems. In addition
to using insulating barrier tape, one way to meet
reinforced isolation requirements is to introduce
further separation between a transformer’s primary
and secondary windings.
Certifying a high-voltage system for reinforced
isolation begins by selecting isolators compliant with
safety and certification testing protocols, as defined
by various committees. Underwriters Laboratories
(UL) is a global safety certification lab in the United
States, but different countries regulate compliance
to their local or regional system standards. Thus,
isolators intended for global use must comply with
various international safety standards.
Table 2 summarizes Verband der Elektrotechnik
(VDE) requirements for capacitive and magnetic
isolators and the International Electro-
technical Commission (IEC) standard directed
at optocouplers.
Insulator rating Description
Functional Insulation necessary for the correct operation of the equipment
Basic Insulation that provides basic protection against electric shock
Supplementary
Independent insulation applied – in addition to basic insulation – in order to protect against electric shock in the event of a failure of the basic insulation
Double Insulation comprising both basic and supplementary insulation
ReinforcedA single insulation system that provides a degree of protection against electric shock equivalent to double insulation
Table 1. Insulation ratings.
TestVDE 0844-11
capacitive and magnetic isolatorsIEC 60747-5-5optocouplers
Basic isolation Reinforced isolation Reinforced isolation only
VIORM – maximum repetitive peak isolation voltage AC voltage (bipolar) AC voltage (bipolar) AC voltage (bipolar)
VIOWM – maximum working isolation voltageAC voltage based on time-dependent dielectric breakdown (TDDB)
AC voltage based on TDDB Based on partial discharge test
VPD – partial discharge test voltage VTEST = 1.5 × VIOWM VTEST = 1.875 × VIOWM VTEST = 1.875 × VIOWM
VIOSM – maximum surge isolation voltage VTEST = 1.3 × VIOSMVTEST = 1.6 × VIOSM 10 kVPK (minimum) 10 kVPK (minimum)
Minimum rated lifetime 20 years × 1.3 20 years × 1.875 Not defined
Failure rate over lifetime 1,000 ppm 1 ppm Not defined
Allowable isolation materials Silicon dioxide (SiO2) and thin-film polymer SiO2 and thin-film polymer Not defined
Table 2. VDE and IEC standards for capacitive and magnetic isolators and optocouplers.
5 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
Isolators have several important parameters.
The creepage and clearance, for example, is the
shortest distance between two conductive leads
across the isolation barrier. As shown in Figure 3,
creepage distance is the shortest distance
measured between adjacent conductors across
the surface of an integrated circuit (IC) package,
whereas clearance distance is measured through
the air.
Package technology plays an important role
in achieving higher measures of creepage and
clearance distance by providing different options
for engineers. High-quality mold compounds,
wide-body packages and higher reinforced isolation
ratings must complement each other, because
higher isolation ratings need wider packages and
better mold compounds so packages don’t cause
breakdown and arcing.
Another parameter is common-mode transient
immunity (CMTI), which indicates an isolator’s
ability to operate reliably in the presence of
high-speed transients and is measured in kilovolts
per microsecond or volts per nanosecond. The
proliferation of wide band-gap semiconductors has
resulted in higher transient voltage (dV/dt) edge
rates, making the measure of CMTI critical for
gauging an isolator’s robustness. High-performance
isolators have CMTI ratings easily reaching 100 V/ns,
and many are tested in excess of 200 V/ns. A low
CMTI isolator operating in a high dV/dt environment
can expect to have signal integrity problems such
as pulse jitter, distortion, erratic operation or missing
pulse information.
Isolation trade-offs are similar at the IC and system
level. Smaller IC package sizes, higher integration,
thermal management and compliance with
certification standards often compete against the
need to reduce electromagnetic interference (EMI)
and achieve higher efficiency. Selecting isolated
components designed to meet all of these needs at
the IC level helps facilitate a seamless transition to
fully reinforced compliance at the system level.
Understanding isolation technologiesICs are the basic building blocks used to achieve
isolation in modern high-voltage systems because
they can block DC and low-frequency AC currents
while allowing power, analog or high-speed digital
signal transfer. Figure 4 on the following page
shows three popular semiconductor isolation
technologies: optical (optocoupler), electric field
signal transfer (capacitive) and magnetic field
coupling (transformer).
Each technology relies on one or more
semiconductor insulating materials, such as those
listed in Table 3, to achieve the required level of
isolation performance. Higher dielectric strength
materials are more effective for isolating similar
voltages over a given distance.
Let’s look at each technology in more depth.
Optical isolation
Optocouplers are complementary metal-oxide
semiconductor ICs used in analog and digital
Figure 3. Creepage (a) and clearance (b) across an
isolator package.
Surface
Air
(a) (b)
Insulator materials Dielectric strength
Air Approximately 1 VRMS/µm
Epoxies Approximately 20 VRMS/µm
Silica-filled mold compounds Approximately 100 VRMS/µm
Polyimide Approximately 300 VRMS/µm
SiO2 Approximately 500 VRMS/µm
Table 3. Semiconductor insulator materials.
6 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
isolation applications. They operate on the principle
of infrared emission from an LED light source
transmitted to a phototransistor through a dielectric
insulating material of air, epoxy or mold compound.
You can see in Table 3 that these materials have
the lowest dielectric strength, and therefore require
more physical separation to achieve higher levels
of isolation.
Although light-emitting photons are the fastest
known vehicles for electromagnetic energy transfer,
LED switching speeds, bias and drive circuitry
limit their signal rate to less than a few megabits
per second. Combining functions such as LED
drive circuitry and amplifiers inside an optocoupler
package helps achieve higher data rates, but at a
higher cost. The input-to-output current transfer
ratio is a measure of an optocoupler’s gain and will
vary and degrade over time. Designers sometimes
compensate for this aging effect by overspecifying
the required bias current. Thus, optocouplers tend
to have higher power consumption compared to
capacitive or magnetic isolators.
Capacitive isolation
Capacitive isolation technology is based on AC
data transfer across a dielectric using schemes
such as on-off keying or edge-based transfer,
as the capacitor inherently blocks DC signals. A
double capacitive isolator is a multichip module
(MCM) consisting of a transmitter (left die) and a
receiver (right die). As shown in Figure 5, each die
has a dedicated capacitor to provide high-voltage
isolation and electric shock protection while meeting
reinforced isolation equivalent to two levels of
basic isolation.
It is possible to place multiple capacitive channels
into a single IC package where either side can
be the transmitter or receiver, thus enabling
bidirectional signal communication. Capacitive
isolators have low propagation delay, can transfer
data at rates exceeding 100 Mbps and consume
less bias current compared to optocouplers – but
still require separate bias supply voltages for each
side of the isolation boundary.
Magnetic isolation
While optocouplers and capacitive isolators are
popular for low-voltage analog and digital signal
transmission, integrated magnetic isolation has
really found its place in high-frequency DC/DC
Figure 5. Block diagram of MCM with isolation capacitors.
Package
LeadframeLeadframe
Left die Right die500 µm
Ciso
Figure 4. Semiconductor isolation technologies:
optocoupler (a); capacitive (b); transformer (c).
Silicon LED
Barrierbreakdowndue to high-
voltage stress
Detector die
Insulatingtape
(a)
(b)
(c)
Left dietransmit/receive
Right dietransmit/receive
High-voltage stress Barrierbreakdown
due tohigh-voltage
stress
Bondwires
Left die
Leadframe
High-voltageSiO capacitors2
Leadframe
Right die
CisolationCisolation
Packagemold compound
7 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
power conversion. A unique advantage of IC
transformer-coupled isolation is the ability to
process power in excess of hundreds of milliwatts,
eliminating the need for a secondary-side
bias supply.
This level of size reduction presents several
challenges, however. First, increasing transformer
isolation through winding separation is counter-
intuitive in an IC package. Second, the height
of traditional ferrite transformers limits their
usage in space-constrained subsystems. Planar
transformers, common in integrated solutions, can
help provide a compact isolated power solution.
There are different implementations of these planar
transformers: air core or magnetic core (magnetic
sheets or ferrite plates placed above and below
the windings). In the absence of magnetic sheets,
air-core transformers are smaller, do not saturate
and are capable of providing medium power-transfer
efficiency with higher output-current capability.
On the other hand, ferrite plates drive higher
coupling between the magnetic core transformer
windings, providing better efficiency with medium
output-current capability. Finally, balancing
the impact of EMI against the need to achieve
reinforced isolation is critical to the successful
adaptation of an IC-level magnetic isolator.
A single isolation solution may not fit every
application, making it necessary to understand
the different parameters and specifications while
balancing design trade-offs.
How isolation requirements differ for end-equipment applicationsIsolation requirements vary greatly across the
industrial, automotive and communication markets.
Even within the same market, different applications
have different isolation requirements. Let’s look at a
few examples.
Grid infrastructure
Figure 6 shows two implementations of solar power
conversion equipment. IEC 62109-1 is the safety
standard driving isolation specifications for these
applications. Depending on the partitioning, basic or
reinforced isolation may be necessary.
In Figure 6, the control module on the left is
accessible externally to this subsystem and to
humans. Isolating the control module from the
high-voltage inverter requires reinforced isolated
gate drivers and isolated sensing. Conversely, the
communications module on the right is already
isolated from the control module by one level of
isolation. The isolation requirements of the gate
Solar PCE
3DCDC
DCDC
PVPV
DC+DC+
DC–DC–
DC–
DC–DC–
DC–
Control/Comms
module µP
Controlmodule
µP
Controlmodule
µP
Communication
bus RS-485,
CAN, Ethernet
High-voltage
solar panel
High-voltage
solar panel
High-voltage
solar inverter
High-voltage
solar inverter
High-voltage
DC/DC converter
High-voltage
DC/DC converter
Isolated IGBT
gate drivers
Isolated IGBT
gate drivers
Isolated current andvoltage sensing
Isolated current andvoltage sensing
Digital
isolator
DC–
Communication
bus RS-485, CAN, Ethernet
Solar PCE
Figure 6. Two architectures for a solar power conversion system.
8 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
drivers and sensing devices are therefore relaxed to
meet functional safety only.
The typical working voltages in these systems are
1 kVRMS to 1.5 kVRMS. For working voltages up
to 1.5 kVRMS, isolators with 8-mm creepage and
clearance may suffice. As working voltages increase
beyond 1.5 kVRMS, conformal coating can help
prevent arcing across pins, but adds system costs.
Alternatively, ultrawide-body package isolators can
support working voltages up to 2 kVRMS.
Factory automation
Programmable logic controller (PLC) applications
process data from 24-V field inputs (from sensors
or transmitters) by transmitting through an isolator
to the MCU. The MCU uses a wired interface such
as RS-485 or Controller Area Network (CAN) for
communication. In the PLC digital input module
shown in Figure 7, the serializer and field side
of the isolator need power from a 5-V or 3.3-V
supply. An isolated power supply or digital isolator
with an integrated power supply providing the
required bias from the MCU side eliminates the
need for a separate power supply on the field side.
Since the field-side voltages are typically 24 V,
functional isolation usually suffices for breaking
the ground loops. Working voltages of 100 VRMS
to 500 VRMS and isolation voltages of 2.5 kVRMS
are good enough for most low-voltage PLC
applications. Packages with small creepage and
clearance distances are preferable in these space-
constrained applications.
Motor drives
The AC drive power stage shown in Figure 8 on
the following page uses isolation for the transfer
of PWM signals to isolated gate drivers, and for
the feedback signals monitoring the voltage and
current for the three phases of the AC motor to
the MCU. Because the high-voltage switching of
the insulated-gate bipolar transistors (IGBTs) and
silicon carbide (SiC) metal-oxide semiconductor
field-effect transistors (MOSFETs) can cause ground
noise in these applications, isolation components
must have high CMTI in order to prevent noise on
the motor side from corrupting data on the MCU
side. The MCU of the drive stage communicates
with the control module using wired interfaces such
as CAN, RS-485 or low-voltage differential signaling
(LVDS). Interfaces such as these could be isolated
depending on the architecture and in some cases
may need isolated power supplies.
Figure 7. PLC digital input module with isolated data and power.
MCU
Protection
circuitry
Protection
circuitry
Protection
circuitry
Signal + Power
isolation
Digital inputField inputs
(0 V to 24 V)
±24 V
5 V/3.3 V available
on controller side
Digital input
serializer
5 V/3.3 V
Isolation barrier
9 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
Automotive applications
With the growth of hybrid electric vehicles
(HEV) and EVs, isolation is increasing in battery
management systems, traction inverters, onboard
chargers, and heating and cooling systems. The
isolation requirements for these systems depend
on their HEV and EV system architectures and
battery voltages.
Figure 9 on the following page shows the battery
management subsystems for a 48-V HEV and a
400-V EV. The isolation components between the
two sides should be able to withstand voltages
and meet the requirements of Verband der
Automobilindustrie 320 (for 48-V systems) and IEC
60664-1 and LV 123 for 400-V/800-V systems.
For 48-V HEVs, small packages are preferable
because of their lower isolation voltages, but for
EVs, batteries operating from higher voltages such
as 400 V or 800 V drive the working voltages
higher, and thus require wider creepage and
clearance packages. Ultra-wide packages are
becoming a critical requirement for high altitude
operation. Isolators in these applications should
have isolated power supplies because bulky
Safe
torque-off
input
3-phase
AC mains
(200 V to 690 V)
Isolation DC/DC
Diagnostics/monitoring
Brake control
Brake
resistorDC LINK
DC LINK
Regen brake power stage
High-side
smart switchIsolated
gate driver
Rectifier
Non-isolated
AC/DC
power
supply
24 V and
other rails
Input power
protectionNon-isolated DC/DC
power supply
Wired interface
Isolated DC/DC main DC link current and
voltage sense Temp monitoring
Signal conditioningMotor current &
voltage sensing
Fan power stage
Connection to control module
Clocking
Fan
Isolated DC/DC hot side
FET
FET
REF REF
EFuse
DC/DC
CAN
Isolation
CMOS
DC/DC
LVDS
RS-485
Supervisor
sequencer
PMICOring
controller
COMP COMP
COMP
LDO
PWM controller
PWM
controller
LDO
LDO
24-V
auxiliary
Multiple
rails
Connection to
control module
Gate
driver
supply
Brake
control
PWM Gate driver supply
3-Phase power stage
Temp
sense
AmpIso
amp
Iso
amp
Isolation
MCU
ASIC
FPGA
Digital processing
Amp
AmpADC
REF
LDO
Logic gates
COMP
Iso delta
sigma
Iso
amp
Isolation Switch/LDO
CLK distribution
Fluxgate/Hall
Logic
gatesIsolated
gate
driver
IGBT
AC
motor
Figure 8. Isolated AC drive power-stage module.
10 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
transformers occupy more board space, whereas
integrated solutions contribute to smaller and lighter
automotive subsystems.
TI technologies for signal and power isolationTI’s isolation ICs use advanced capacitive isolation
technology for signal isolators and proprietary planar
transformer and control technology for magnetic
isolation. TI leverages its position in package
development, isolation and process technology
to achieve the highest levels of integration,
performance and reliability.
For signal isolation, TI’s capacitive isolators are
constructed using a SiO2 dielectric, which has the
highest dielectric strength of the materials listed in
Table 3. TI’s data or signal isolators use a logic input
and output buffer separated by a double capacitive
SiO2 insulation barrier, as shown in Figure 10 on the
following page.
SiO2, in addition to having the highest dielectric
strength among other insulators, is also an inorganic
material and therefore very stable over moisture
and temperature. TI’s proprietary methodology for
multilayered capacitor and multilayer passivation
improves isolator quality and reliability by reducing
the dependence of high-voltage performance on
any single layer. This technology supports working
voltages (VIOWM) of 2 kVRMS, withstand isolation
voltages (VISO) of 5.7 kVRMS, and surge voltage
capability of 12.8 kVPK.
Isolators must have long lifetimes – well beyond
those of non-isolated components – in order to
CSU passive cell balancing
400-V battery pack – passive balancing48-V battery pack – passive balancing
12-V
supply
48-V
battery
Contactor
control
Isolated
DC/DC power
supply
CAN
Current and
voltage sense
Self diagnostics/
monitoring
Reverse battery
protection
System basis
chip (SBC)
Input
protection
DC/DC
converter/
SBC
High-side &
low-side
switches
Temperature
& voltage
measurements
Cell
supervision
AFE
(M&P)
Isolated
DC/DC
Microcontroller
CAN
transceiver
Isolator
CAN Digital processing Battery monitoringSignal
isolation
..
..
Real-time
clock &
monitor
Interlock
High-voltagesafety interlock
CANCAN
transceiver
CAN
Pack
thermal
management
Valve control
12-V
supply
High-side &
low-side
switches
Microcontroller
Input
protection
Contactor control
Battery systemcontroller
Reverse battery
protection
Watchdog
Battery control unit
Current
sense
StepdownHV-12
DC-DCconverter/
SBC
Monitoring &overcurrent detection
CSC interfacecontroller
supply
High-voltagediagnostics
Current
sense
Isolator
enable
Isolation
checks
Isolator
Signalisolation
Safetydiagnostics
CSC interfacecontroller
Microcontroller
Cellsupervisiondiagnostics
High-
voltage
diagnosis
CSU
interface
CSC interface
CSUx
CSU2
CSU1
Isolated
supply
IsolatedDC/DC power
supply
CANDigital
isolator
Cellsafety
Temperature
sense
CSC supply
CSC controllerBCU interface
DC/DC
power
supply
MCU
(Optional)
Cell diagnostics Battery monitoring
Cell supervision
(monitor &
protection)
DC/DC
converter/
SBC
System basischip (SBC)
Figure 9. Battery pack subsystems for 48-V HEVs and 400-V EVs.
11 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
protect circuitry from faults. One test for determining
an isolator’s lifetime is the TDDB test, which
measures the time to failure after applying a high
voltage across the device to extrapolate its lifetime.
Figure 11 shows that the lifetime of TI’s reinforced
SiO2 isolators exceed 100 years, well above the
industry standard, and beyond the lifetime of the
insulating materials in Table 3.
While absolute TDDB lifetime is important for
all applications, lifetime variation with switching
frequencies also matters. One example is the
motor-control system shown in Figure 8, where it’s
important to preserve the isolator’s lifetime over the
entire range of various switching frequencies. The
lifetime curves of the SiO2-based capacitive isolator
in Figure 12 highlight that these devices have very
low lifetime variation with frequency.
Transmit chip Receive chip
OOKmodulation
RXsignal
conditioningEnvelope
detection
TXsignal
conditioning
Bottom electrode
ILDn–1>10.5 µmLayers of SiO dielectric2
ILDn
...
...
HV capacitor top electrode
Wire
bond
Figure 10. SiO2-based capacitive isolation technology.
Figure 11. Lifetime performance of an SiO2-based
capacitive isolator.
T up to 150°C
Modeled insulation lifetime = 135 yearsA Stress voltage frequency = 60 Hz
Working isolation voltage = 1500 VRMS
Applied voltage (V )RMS
Figure 12. AC TDDB for a capacitive isolation device with SiO2
dielectric as a function of frequency.
5-kV peak
1.0E+07
1.0E+06
1.0E+05
1.0E+04
1.0E+03
1 10 100
Frequency (Hz)
TD
DB
lif
eti
me (
sec)
1,000 10,000
6-kV peak
8-kV peak
�
�
�
�
12 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
Another test that TI uses to demonstrate process
capability is the ramp to breakdown voltage
distribution shown in Figure 13. The industry
requirement for most applications is 5.7 kVRMS or
below, while TI’s test data shows process capability
above 10 kVRMS, demonstrating considerable
margin of this stable process technology.
Figure 13. Ramp to breakdown voltage distribution
(1-kVRMS/s ramp rate).
RTB kV (16 bins)RMS
(Row
count)
5.00
500
450
400
350
300
250
200
150
100
50
0
6.00 7.00 8.00 9.00 10.00 11.00 13.00 14.0012.00
N =
Mean =
StDev =
180
12.35 kV
0.26 kVRMS
RMS
VIOTM
TI uses this capacitive isolation technology in several
product families supporting functional, basic and
reinforced ratings and commercial, automotive and
high-reliability devices. For example:
• To address the variety of specifications, TI’s
portfolio has several digital isolator families that
range from providing the highest isolation and
widest packages to the lowest power.
• Integrating various transceivers such as
RS-485, CAN or LVDS with digital isolators
provides single-chip isolated transceivers for
communication to and from the microcontroller.
• Isolated gate drivers accept a low-power input
from a controller IC to produce the appropriate
high-current gate drive for a MOSFET, IGBT, SiC
or gallium nitride power switch.
• Isolated amplifiers (analog output) and
isolated modulators (digital output) can be
used for cost-sensitive current- and voltage-
sensing applications.
For magnetic isolation, TI uses a proprietary
multichip module approach, co-packaging a
planar transformer with an isolated power stage
and dedicated controller die. The total solution
is integrated into a 2.65-mm-high wide-body
small-outline IC package, resulting in a DC/DC
bias converter capable of reinforced isolation up to
10 kVPK and 5 kVRMS, according to the magnetic
isolator requirements outlined in Table 2.
The dual-die multichip module shown in Figure 14
on the following page uses specialized control
mechanisms; clocking schemes; and a high-Q
integrated planar transformer to provide low
radiated emissions, high efficiency and exceptional
thermal performance. The transformer topology may
consist of optional top and bottom ferrite plates,
with TI’s proprietary thin-film polymer laminate
array as the insulation barrier. The transformer
configuration shown in Figure 14 is an example
of transformer windings contained within the
polymer laminate sandwiched between two parallel
ferrite plates.
TI’s magnetic shielding techniques constrain the
magnetic flux, providing more effective magnetic
coupling and better radiated EMI performance
compared to air-core transformers. Employing EMI
mitigation techniques at the package level eliminates
the need for additional board-level filtering to
meet the limits of Comité International Spécial des
Perturbations Radioélectriques (CISPR) 32 Class B
radiated emissions. Figure 15 on the following page
demonstrates better than –5 dB of margin with four
UCC12050 DC/DC converters operating simul-
taneously and unsynchronized.
Thermal management and efficiency define the
boundary conditions for power delivery within a
given package. TI’s proprietary control and fault
13 April 2021High-Voltage Semiconductor Solutions for Meeting Isolation Requirements
algorithms, designed to reduce power loss and
boost efficiency, can achieve cohesive integration
between the transformer and silicon. Figure 16
shows the resulting efficiency curves for a 5-V
input, 500-mW isolated bias converter for four
user-selectable output options.
The black curve shown in Figure 16 highlights
peak efficiency of nearly 60% operating at a 25°C
ambient temperature and a full load current of
100 mA for VISO = 5 V. Under the same operating
conditions, Figure 17 shows thermal performance
16°C above a 25°C ambient temperature. Fully
rated load power up to 60°C is possible with 20%
derating at a 125°C ambient temperature.
Figure 18 on the following page shows a
multichannel reinforced digital isolator family with
an integrated high-efficiency power converter to
VINP
SEL
VISO
GNDS
UVLO
OSC
EN
SYNC
SYNC_OK
GNDP
Ext CLK
detect
Transformer
driverRectifier
Control
�2
Figure 14. The UCC12050 500-mW DC/DC converter.
Frequency (kHz)10010 1000
Lim
it (
dB
µv/M
)
60
50
40
30
20
10
0
–10
Figure 15. Four 5-V to 5-V 500-mW DC/DC converters.
Load current (mA)
Effi
cie
ncy
(%
)
0 20 40 60 80 100 120 1400
10
20
30
40
50
60
70
V ISO = 5.4 VV ISO = 5.0 VV ISO = 3.7 VV ISO = 3.3 V
Typical efficiency vs. Load
VINP = 5.0 V TA = 25ºC
Figure 16. 5-V to 5-V magnetic isolator: efficiency vs. load.
Figure 17. 5-V to 5-V, 500-mW and 25°C (16°C above
ambient) thermal performance.
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drive external transceivers, amplifiers and ADCs.
The signal isolation channel has a logic input and
output buffer separated by a double capacitive SiO2
insulation barrier, whereas power isolation uses
on-chip transformers separated by thin-film polymer
as insulating material. Both signal and power paths
are 5-kVRMS isolated, with the integrated DC/DC
converter providing up to 650 mW of isolated
power. Innovative chip design and layout techniques
leading to significantly enhanced electromagnetic
compatibility ease system-level electrostatic
discharge, electrical fast transient, surge and
emissions compliance. These devices have included
protection features such as soft start to limit inrush
current, overload and short-circuit protection, and
thermal shutdown. Further integration with an
RS-485 transceiver or isolated amplifier enable
single-supply operation from the low side of
these subsystems.
ConclusionIn industrial and automotive applications, isolation
enables communication between different voltage
domains by protecting low-voltage circuitry
from high-voltage faults and maintaining signal
integrity by breaking ground loops. Of the different
dielectric materials available for isolation, the
SiO2 dielectric used in TI’s capacitive isolators
offers the highest lifetime in the industry, along
with stability over moisture and temperature.
TI’s integrated transformer technology enables
high-density isolated DC/DC power conversion
while lowering EMI.
The TI portfolio of signal and power isolators helps
engineers by ensuring compliance with the most
stringent isolation system requirements. See
ti.com/isolationtechnology to learn how
to increase safety with high working voltage
and reliability.
Key product categories for isolation
Isolated bias supplies
Isolated gate drivers
Digital isolators
Isolated ADCs
Isolated amplifiers
Isolated interfaces
V
V
V
CC
ref
ISOTransformer
driver
FB channel
(Rx)
FB channel
(Tx)FB
controller
UVLO, soft-start
I/O channels I/O channelsData channels
(4)
Data channels
(4)
Power
controller
Thermal
shutdown,
UVLO, soft-start
Rectifier
Transformer
Isolation barrier
Figure 18. The ISOW7841 DC/DC converter plus four
high-speed data channels.
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