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TPS61087-Q1

SLVSB50

– DECEMBER 2011

www.ti.com

Inductor Selection

The TPS61087-Q1 is designed to work with a wide range of inductors. The main parameter for the inductor

selection is the saturation current of the inductor which should be higher than the peak switch current as

calculated in the Design Procedure section with additional margin to cover for heavy load transients. An

alternative, more conservative, is to choose an inductor with a saturation current at least as high as the

maximum switch current limit of 4.8 A. The other important parameter is the inductor DC resistance. Usually the

lower the DC resistance the higher the efficiency. It is important to note that the inductor DC resistance is not the

only parameter determining the efficiency. Especially for a boost converter where the inductor is the energy

storage element, the type and core material of the inductor influences the efficiency as well. At high switching

frequencies of 1.2 MHz inductor core losses, proximity effects and skin effects become more important. Usually

an inductor with a larger form factor gives higher efficiency. The efficiency difference between different inductors

can vary between 2% to 10%. For the TPS61087-Q1, inductor values between 3

μH and 6 μH are a good choice

with a switching frequency of 1.2 MHz, typically 3.3

μH. At 650 kHz we recommend inductors between 6 μH and

13

μH, typically 6.8 μH. Possible inductors are shown in Table 1.

Typically, it is recommended that the inductor current ripple is below 35% of the average inductor current.

Therefore, the following equation can be used to calculate the inductor value, L:

(5)

with

Minimum input voltage

Output voltage

Maximum output current in the application

Converter switching frequency (typically 1.2 MHz or 650 kHz)

η

Estimated converter efficiency (please use the number from the efficiency plots or 90% as an estimation)

Table 1. Inductor Selection

L

COMPONENT

SIZE

DCR TYP

SUPPLIER

CODE

(

μH)

(L

×W×H mm)

(m

Ω)

1.2 MHz

4.2

Sumida

CDRH5D28

5.7

× 5.7 × 3

23

2.2

4.7

Wurth Elektronik

7447785004

5.9

× 6.2 × 3.3

60

2.5

5

Coilcraft

MSS7341

7.3

× 7.3 × 4.1

24

2.9

5

Sumida

CDRH6D28

7

× 7 × 3

23

2.4

4.6

Sumida

CDR7D28

7.6

× 7.6 × 3

38

3.15

4.7

Wurth Elektronik

7447789004

7.3

× 7.3 × 3.2

33

3.9

3.3

Wurth Elektronik

7447789003

7.3

× 7.3 × 3.2

30

4.2

650 kHz

10

Wurth Elektronik

744778910

7.3

× 7.3 × 3.2

51

2.2

10

Sumida

CDRH8D28

8.3

× 8.3 × 3

36

2.7

6.8

Sumida

CDRH6D26HPNP

7

× 7 × 2.8

52

2.9

6.2

Sumida

CDRH8D58

8.3

× 8.3 × 6

25

3.3

10

Coilcraft

DS3316P

12.95

× 9.40 ×

80

3.5

5.08

10

Sumida

CDRH8D43

8.3

× 8.3 × 4.5

29

4

6.8

Wurth Elektronik

74454068

12.7

× 10 × 4.9

55

4.1

10

Copyright

© 2011, Texas Instruments Incorporated