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ADP3170JRU

VRM 8.5 Compatible Single Phase Core Controller

Analog Devices 

ADP3170

Designing an Inductor

Once the inductance is known, the next step is either to design

an inductor or find a standard inductor that comes as close as

possible to meeting the overall design goals. The first decision

in designing the inductor is to choose the core material. There

are several possibilities for providing low core loss at high fre-

quencies. Two examples are the powder cores (e.g., Kool-M®

from Magnetics, Inc.) and the gapped soft ferrite cores (e.g.,

3F3 or 3F4 from Philips). Low frequency powdered iron cores

should be avoided due to their high core loss, especially when

the inductor value is relatively low and the ripple current is high.

Two main core types can be used in this application. Open

magnetic loop types, such as beads, beads on leads, and rods

and slugs, provide lower cost but do not have a focused mag-

netic field in the core. The radiated EMI from the distributed

magnetic field may create problems with noise interference in

the circuitry surrounding the inductor. Closed-loop types,

such as pot cores, PQ, U, and E cores, or toroids, cost more, but

have much better EMI/RFI performance. A good compromise

between price and performance are cores with a toroidal shape.

There are many useful references for quickly designing a power

inductor. Table II gives some examples.

Table II. Magnetics Design References

Magnetic Designer Software

Intusoft (http://www.intusoft.com)

Designing Magnetic Components for High-Frequency DC-DC

Converters

McLyman, Kg Magnetics

ISBN 1-883107-00-08

L1

1.7␮H

5V

D1

MBR052LT1

12V

C1

1000␮F

C2

1000␮F

C6

C7

4.7nF 100nF

C3

1000␮F

C4

1000␮F

U1

ADP3170

5V SB

D2

MBR052LT1

FROM

CPU

VTT PWRGD CLK

1 VID3

2 VID2

3 VID1

4 VID0

5 VID25

6 PWRGD

7 REF

8 SD

9 FB

10 CS–

GND 20

PGND 19

DRVH 18

DRVL 17

VCC 16

LRFB 15

LRDRV 14

COMP 13

CT 12

CS+ 11

C5

1000␮F

C12

22␮F

Q1

FDB7045L

L1

1␮H

R6

2.5m⍀

1000␮F ؋ 8

RUBYCON ZA SERIES

24m⍀ ESR (EACH)

Q2

FDB7045L

C13 C14 C15 C16 C17 C18 C19 C20

C19

150pF

COC

2.7nF

RB

30.1k⍀

1%

RA

13.7k⍀

1%

C22

68pF

5V SB R7

Q6

10k⍀

IRL3103

C21

1␮F

C8

100pF

R1

1k⍀

C11

1nF

R4

220⍀

R5

220⍀

C23

220␮F

Figure 3. 24 A VRM 8.5-Compliant CPU Supply

VCC(CORE)

1.05V – 1.825V

23A

VCC(CORE) RTN

1.8V SB

1.8V, 200mA

CORE

PWRGD

TO CPU

REV. 0

–9–

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