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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