apec 2020 industry sessions - we-online.com · buck-boost automotive usb-pd type c –14vin 350khz...

Hebberly Ahatlan

Product Marketing Manager Analog Devices

Keith Szolusha

Sr. Applications Manager Analog Devices

Quentin Laidebeur

Team Lead Product Definition Engineering America

APEC 2020

Industry Sessions

5 March 2020 ©2020 Analog Devices, Inc. All rights reserved.1

Practical DC/DC EMI

improvement

techniques

Understanding the inductor’s EMC role at the

switching node

©2020 Analog Devices, Inc. All rights reserved.2 5 March 2020

Introduction

It is well understood that a power MOSFET in a SMPS

contributes high voltage ringing that propagates across traces

and components and causes compatibility issues.


V

Simplified Boost DC/DC

A typical conducted path for the MOSFETs noise is the switching

side of the inductor.


V


Introduction

Since the inductor output lead and the switching node are

practically the same point in most designs, the inductor can be

both a victim of the MOSFET noise and an amplifier of it.


V


Introduction


V


To mitigate this SW node noise we can attempt any combination

of these three solutions:

Change the layout

Change the inductor

Shield the noise node

In this presentation we will explore each of these

methods and offer tips along the way to optimize

them.

Introduction

Changing the

layout

Tips on changing layout to improve inductor immunity


Identifying Parasitic Antennas


Long traces on a board can

interact with the inductor

L

Fsw

Is λ of Fsw = L~ 1/2𝑛𝑛 = 𝑤ℎ𝑜𝑙𝑒 𝑛𝑢𝑚𝑏𝑒𝑟

The effects of via and trace orientation


Direction of H-field affects

magnetic coupling among

nearby components

Fsw H

Repositioning traces and planes


Distance and surface area

affect field coupling

Fsw

USB-PD Type C Buck-Boost Automotive Charger

Feburary 4, 2020 Analog Devices Highly Confidential Information. ©2020 Analog Devices, Inc. All rights reserved.11

Inductor Orientation 1

Short-Terminal on Buck-SW Side

Inductor Orientation 2

Short-Terminal on Boost-SW Side

Buck-Boost Automotive USB-PD Type C – 14VIN

350kHz 20V 3A PDO (Boost) and 9V 3A PDO

(Buck)

► 350kHz fsw for this application

► SSFM

► Run CISPR 25 emissions testing with L1 6.8 uH inductor in two different assembly orientations.

Does it matter which way it is assembled?

► Check Radiated and Conducted Emissions – Peak and Average


-10

0

10

20

30

40

50

60

0.1 1 10 100 1000

AV

ER

AG

E R

AD

IAT

ED

EM

ISS

ION

S [d

Bµ

V/m

]V

ER

TIC

AL

PO

LA

RIZ

AT

ION

FREQUENCY [MHz]

-10

0

10

20

30

40

50

60

0.1 1 10 100 1000

AV

ER

AG

E R

AD

IAT

ED

EM

ISS

ION

S [d

Bµ

V/m

]V

ER

TIC

AL

PO

LA

RIZ

AT

ION

FREQUENCY [MHz]

Inductor Has Best Emissions When Short

Terminal is Placed on Active SW Node.


L1 Orientation 1

L1 Orientation 2

CISPR25 Limits Class 5

14VIN 20VOUT 3A (60W)

2-SW BOOST


2-SW BUCK

Radiated Emissions

-50

-30

-10

10

30

50

0.1 1 10 100

AV

ER

AG

E C

ON

DU

CT

ED

EM

I [d

BµA

]750m

m

FREQUENCY [MHz]

-50

-30

-10

10

30

50

0.1 1 10 100

AV

ER

AG

E C

ON

DU

CT

ED

EM

I [d

BµA

]750m

m

FREQUENCY [MHz]

Inductor Has Best Emissions When Short Terminal

is Placed on Active SW Node.


L1 Orientation 1

L1 Orientation 2



2-SW BOOST


2-SW BUCK

Conducted Emissions – Current Probe

-20

-10

0

10

20

30

40

50

60

70

80

0.1 1 10 100

AV

ER

AG

E C

ON

DU

CT

ED

EM

I [d

BµV

]

SU

PP

LY

FREQUENCY [MHz]

-20

-10

0

10

20

30

40

50

60

70

80

0.1 1 10 100

AV

ER

AG

E C

ON

DU

CT

ED

EM

I [d

BµV

]

SU

PP

LY

FREQUENCY [MHz]

Inductor Has Best FM Band Voltage CE When Short

Terminal is Placed on Active SW Node.


L1 Orientation 1

L1 Orientation 2



2-SW BOOST


2-SW BUCK

Buck-Boost Automotive USB-PD Type C – 14VIN

400kHz 20V 3A PDO (Boost) and 9V 3A PDO

(Buck)

Result Summary:

► Inductor orientation makes a very significant impact on CISPR 25 emissions results

► The best emissions in boost operation (20V output) occur when the short-side terminal is assembled

on the boost SW.

► The best emissions in buck operation (9V output) occur when the short-side terminal is assembled

on the buck SW.


05.03.2020 17

Changing the

inductor Tips on changing inductors to mitigate radiated compatibility

05.03.2020 18

Start of Winding Effect on EMI

Performance

Multiple layer Inductors Single layer Inductors

05.03.2020

Inductor Material Effect

19

-Iron Powder

-Soft saturation

-Good Shielding

-Ferrite

-Hard saturation

-Good Shielding

-High Permeability Alloys

-Medium saturation

-Good Shielding

05.03.2020

Inductor Construction and

Winding Orientation

20

Gapped construction / Flat wire

VerticalGapped construction / Round wire

Horizontal

Distributed gap / Flat wire

Vertical

TO

P V

IEW

Shielding the noise

source

Tips on the benefits and drawbacks of shielding


Types of shielding



LED Driver Prototype PCB – 12VIN 250kHz

45V 500mA LED String

LED Driver Prototype PCB – 12VIN 250kHz 45V

500mA LED String

► Low EMI Silent-Switcher Monolithic 60V 3A IC with High Dimming Ratio

► 2-SW Synchronous Boost LED Driver

► 250kHz fsw for this application

► SSFM

► Run CISPR 25 emissions testing with two different shields to see if the solid shield is more effective

than the shield with holes in it.

► Shield is clipped onto PCB

► Shield is effective to pass very low emissions requirements for certain customers.


Buck-Boost USB-PD Type C – 14VIN 400kHz 20V

3A PDO (Boost) and 9V 3A PDO (Buck)

Result Summary:

► Both shields act the same.

► Further work is required to see if soldering a shield directly to the PCB ground is more effective than

using clips.


Both Shields Reduce the Already Low Radiated

Emissions Above 10MHz


No Shield

Standard Shield With Holes

Solid Shield With No Holes


Both Shields Have Similar Results

Red and Green Shield Plots Are Equal

Both Shields Reduce the Already Low Current

Probe Conducted Emissions Where it is Critical


No Shield




Both Shields Have Similar Results


Both Shields Reduce the Already Low Current

Probe Conducted Emissions Where it is Critical


No Shield




Both Shields Have Similar Results – Need > LC Input Filter


LT8386 HUD LED Driver

Feburary 24-28, 2020 Analog Devices Highly Confidential Information. ©2020 Analog Devices, Inc. All rights reserved.29

► Shield mount

► Output caps and hot-

loop caps testing

► PWM switch and filter

► Input filter

AM band

All frequencies

► 250-400kHz applications

(preferred by customer)

► Silent Switcher 1

► LT8386 or LT3922-1

► EMI filters

► 10k:1 150Hz PWM Dimming

9-16VIN

With output filter

50k:1 PWM dim with no filter

► 4k:1 1kHz Daimler Spec

► Shield mount and tested

► 45V 500mA LEDs

Conclusions and

Q&A


Contact ADI or Wurth for

more information


Hebberly Ahatlan

Product Marketing Manager Analog Devices

Keith Szolusha

Sr. Applications Manager Analog Devices

Quentin Laidebeur

Team Lead Product Definition Engineering America

Thank you


apec 2020 industry sessions - we-online.com · buck-boost automotive usb-pd type c –14vin 350khz...

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