Datasheet

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IN S IN
S
out S
V V V
L
V I f
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TPS61087
SLVS821C MAY 2008REVISED JULY 2013
www.ti.com
Inductor Selection
The TPS61087 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, 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
V
IN
Minimum input voltage
V
S
Output voltage
I
out
Maximum output current in the application
f
S
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 I
sat
(A)
CODE
(μH) (L×W×H mm) (m)
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
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