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Welcome to the Webinar:Calculating the best Power Inductor Solution

1. April 2020


Technical Disclaimer

Statements of suitability for certain applications are based on ourknowledge of typical operating conditions for such applications,but are not intended to constitute – and we specifically disclaim –any warranty concerning suitability for a specific customerapplication or use. This Information is intended for use only bycustomers who have the requisite experience and capability todetermine the correct products for their application. Any technicaladvice inferred from this Information or otherwise provided by uswith reference to the use of our products is given gratis, and weassume no obligation or liability for the advice given or resultsobtained.


Overview

1. Basics – What is an Inductor?

2. DCDC Converter – Where do I need Power Inductors?

3. Calculating the inductor values – How can I find the best component?

4. KEMET Power Inductors – Which Power Inductors does KEMET offer?


Basics

Magnetics


Inductor mechanical parameter

6


Inductance

o Component inductance is a function of

• core material and permeability, geometry and cross section area of the core

• Turn number, airgap (if existing)

7


Factors influencing inductance

o Increased inductance with...

• Higher permeability

• Bigger cross section of the core

• Higher number of turn

• Less effective lenght of the core

o To keep the component performance but having a higher permeability...

• Lower cross section of the core -> less weight / smaller size

• Less turns -> use thinner wire to get the same RDC resistance

Example with a circular core

µr = 18000

µr =

15000

µr =

10000

8


DC-DC Converter


DC-DC Converter

o Switching Frequency

• Typical Switching frequency is between 30 kHz and 1MHz

• Most common Switching Frequencies are from 300kHz to 1MHz

• As switching frequency increases, the inductor size is reduced

• The current from a switching regulator has AC components that will flow through the output capacitor

• The output capacitor ESR defines the ripple voltage generated by the AC component of the current

10


Buck Converter

o Parts of a DCDC Converter:

• Switch (Transistor, IC)

• Diode

• Inductor

• Capacitor

o Switching frequency

defines On and Off

phase

11


Buck Converter

o On Phase

• Current flows from Source through T, L and C

12


Buck Converter

o Off Phase

• Current flows through D, L and C

13


Buck Converter

o All Phases

14


Calculating theInductor values


DC-DC Converter

o The amount of inductance needed is determined by

• Output voltage

• Input voltage (max)

• Switching frequency (IC and EMI)

• Maximum ripple current

o The output current (Iout) of the regulator should be less than the maximum rated current of the inductor.

16


DC-DC Converter

o Buck Converter

𝐿 =(𝑉𝑖𝑛 − 𝑉𝑜𝑢𝑡) ∙ (𝑉𝑜𝑢𝑡 + 𝑉𝐷)

(𝑉𝑜𝑢𝑡 + 𝑉𝐷) ∙ 𝑟𝑐𝑟 ∙ 𝐼𝑜𝑢𝑡 ∙ 𝑓

VD Diode Voltage Loss (~0,5V for Schottky)

Vin Maximum Input Voltage

o Example: Vin = 36V / Vout = 5V / Iout = 1A / Vripple = 40mV / f = 350kHz

𝑑𝑖 =𝑉𝑟𝑖𝑝𝑝𝑙𝑒𝐸𝑆𝑅

=40𝑚𝑉

120𝑚Ω= 0,33𝐴

𝑟𝑐𝑟 =𝑑𝑖

𝑑𝑡=0,33𝐴

1𝐴= 0,33

17


DC-DC Converter

o Inductor Calculation

𝐿 =(36𝑉 − 5𝑉) ∙ (5𝑉 + 0,5𝑉)

(36𝑉 + 0,5𝑉) ∙ 0,33 ∙ 1𝐴 ∙ 350𝑘𝐻𝑧= 40,44𝜇𝐻

o Which Inductance? 33µH? 47µH? 39µH?

• 47µH: „Max current is lower, RDC is too high or item is too big…“

• 39µH: „Special item, not available from all manufacturers …“

• 33µH: „Let‘s try this one!“

18


Inductor Selection

o Let‘s assume we have 10% Inductance loss (Saturation, Tolerance …)

o So our remaining Inductance = 30µH

o 30µH Inductance is 25% less than calculated (40,44µH)!

𝐿 =(𝑉𝑖𝑛 − 𝑉𝑜𝑢𝑡) ∙ (𝑉𝑜𝑢𝑡 + 𝑉𝐷)

(𝑉𝑜𝑢𝑡 + 𝑉𝐷) ∙ 𝑟𝑐𝑟 ∙ 𝐼𝑜𝑢𝑡 ∙ 𝑓

o V, I and f are constant, so 25% lower Inductance means 33% higher ripple current!

o Higher Inductance Value should be prefered! → 47µH

o Why 25% lower Inductance is not 25% higher ripple current???

• Because: 25% lower L is 75% = 0.75 = Τ3 4→ Τ4 3 iripple = 1.33 iripple

19


Inductor Selection

o Reading the Datasheet

o 3 Current Values are given

20


Rated Current

o Irms is when the temperature rise of of the inductor is 40K above ambient temperature

o Isat is when the inductance drops by 20% / 30% (saturation)

0,1 0,5 0,9 1,3 1,7 2,1 2,5 2,9 3,3 3,7 4,1 4,5 4,9

T(K) L

Irms : temperature rise

Isat : Inductance drop-20%

+40K

21


Rated Current

o Temperature rise and Saturation are not standard values and can vary for different manufacturers or even for one manufacturer

• Example:

22


Rated Current: Irms

o Ambient temperature + temperature rise must be lower than the maximum operatingtemperature of the inductor

• Example:

• Ambient temperature = 85°C (Application)

• Maximum operating temperature = 155°C (MPX)

• Maximum temperature rise of the inductor = 155°C – 85°C = 70°C

0,1 0,5 0,9 1,3 1,7 2,1 2,5 2,9 3,3 3,7 4,1 4,5 4,9

Ambient temperature

Irms

max temp of the inductor

Imax 23

+40K


Rated Current: Isat

o Saturation Current describes one point on the Inductance over Current graph

o Ideally, the Current and Ripple must be checked for each Inductor

• What is the output current?

24

0

5

10

15

20

25

30

35

40

45

50

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9 1

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9 2

2,1

2,2

2,3

2,4

2,5

2,6

2,7

Metcom 47µH Standard 47µH Metcom 33µH


Rated Current: Isat

o Influence of Ripple

o Example @ 1.5A

25

0

5

10

15

20

25

30

35

40

45

50

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9 1

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9 2

2,1

2,2

2,3

2,4

2,5

2,6

2,7

Ripple

Inducta

nce

Output Current


Rated Current: Isat

o Influence of Ripple with Soft Saturation Inductor

o Example @ 1.5A

26

0

5

10

15

20

25

30

35

40

45

50

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9 1

1,1

1,2

1,3

1,4

1,5

1,6

1,7

1,8

1,9 2

2,1

2,2

2,3

2,4

2,5

2,6

2,7

Ripple

Inducta

nce

Output Current


Rated Current: Isat

o Inductance drop must still work with the ripple current

• A Decrease of the inductance is equivalent to an Increase of the ripple current!

• Ripple Current should be as low as possible

Inductor in

saturation

Inductor not in

saturation

27


Comparing Datasheets: Same item???

28

Max. 3.3A @ 85°C Max. 2.2A @ 85°C

KEMET:

Max. 4.5A @ 115°C

=

> 4.5A @ 85°C


Summary Rated Current

o Saturation Current and RMS Current:

• Isat and Irms are independent and need to be considered seperately

• Each application must be considered concerning:

• ambient temperature and maximum Inductor temperature for Irms

• maximum ripple current of the DCDC converter for Isat

o Isat and Irms are no limitations, but the max operating temperature is a limitation

29


General Inductor requirements

o Low RDC for less DC losses and high Irms : KEMET MPX with high Irms

o Operating Temperature range indicates maximum current: KEMET MPX up to 155°C

o Smooth saturation for high ripple currents: KEMET METCOM technology of MPX

o Molded design for low EMI : KEMET METCOM technology of MPX

o Optimzied Material for high switching frequencies: KEMET METCOM technology of MPX

30


KEMET Power Inductors


Metal Composite (Power) Inductors

o Metal Powder / Iron Powder / Metal Composite …


Material technology for Metal Composite Inductors

o Core Structure of the Metal Composite Inductor

27

Insulating coating : Own design and process

Metal powder : Material Technology

Binder

High

performance/reliability for

operating voltage

33


By Maxwell 3D

Load 1.8A

1div = 1mm

TOP View Side View

Molded : MPLCV0654L330

Core type : Metal

Molded

Inductance : 33 uH

DCR : 154 mΩ

Isat : 4.0 A

Idc : 2.6 A

Assembled Inductor

Core type : Ferrite

Assembled

Inductance : 33 uH

DCR : 175 mΩ

Isat : 2.6 A

Idc : 2.0 A

Comparison of the Leaking amount Magnetic Flux

Detail of model

The metal molded type is better for magnetic flux leaking than an assembled type.

A ferrite inductor has some aperture since it’s assembled type typically. Magnetic Flux leaks from aperture.

Molded vs. Assembled Inductor

o Magnetic Field

34


Molded vs. Assembled Inductor

o Saturation Current

DC-superposed Characteristics

Assembled(25)

Assembled(125)

Metal molded(25)

Metal molded(125)

Metal molded type

Inductance : 33uH

size : 6.7mm x H5.4mm

Assembled type

Inductance : 33uH

size : 7mm x H6mm

The metal molded type has advantage to the assembled type

• Stateable characteristic by the temperature

• High saturation flux density

35


Product Overview

o MPX (Standard) / MPXV (Automotive) Power Inductor Series

• Metal composite shielded Inductor

• Inductance range from 0,10µH – 100,00µH

• Rated Current Range 2A – 90A

• 15 different Case Sizes from 5 x 5 x 2mm up to 22 x 22 x 13mm

• Operating temperature up to +155°C

36


Contact

o Alexander Nebel Dipl.-Ing. (FH)

o Field Application Engineer

o (+49) 162 - 13 54 276

o [email protected]

Thank you.

Welcome to the Webinar: Calculating the best Power … › wp-content › uploads › sites › 4...

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