x

Where D =

(2 x L x f)

DQG '¶ = (1 - D)

'¶

For Boost

TPS61193

www.ti.com

SNVSAF4 – OCTOBER 2015

Typical Applications (continued)

8.2.1.1 Design Requirements

DESIGN PARAMETER

VALUE

4.5…28 V

LED string

3P8S LEDs (30 V)

LED string current

100 mA

Maximum boost voltage

37 V

Boost switching frequency

300 kHz

External boost sync

not used

Boost spread spectrum

enabled

L1

33

μH

10 µF 50 V

2 × (10 µF 50-V ceramic) + 33 µF 50-V electrolytic

2 × (10 µF 50-V ceramic) + 33 µF 50-V electrolytic

15 pF

1 µF 10 V

24 k

Ω

210 k

Ω

R1

750 k

Ω

R2

130 k

Ω

R3

10 k

Ω

8.2.1.2 Detailed Design Procedure

8.2.1.2.1

Inductor Selection

There are two main considerations when choosing an inductor; the inductor should not saturate, and the inductor

current ripple should be small enough to achieve the desired output voltage ripple. Different saturation current

rating specifications are followed by different manufacturers so attention must be given to details. Saturation

current ratings are typically specified at 25°C. However, ratings at the maximum ambient temperature of

application should be requested from the manufacturer. Shielded inductors radiate less noise and should be

preferred. The saturation current should be greater than the sum of the maximum load current and the worst

case average to peak inductor current. The equation below shows the worst case conditions

•

•

•

•

L - min inductor value including worst case tolerances

•

f - minimum switching frequency

•

•

D - Duty Cycle for CCM Operation

•

(4)

approach is to choose an inductor that has a saturation current rating greater than the maximum current limit. A

saturation current rating of at least 2.5 A is recommended for most applications. See Table 2 for recommended

inductance value for the different switching frequency ranges. The inductor’s resistance should be less than

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