©

§

2 x L

©

§

x

x

1

f

©

§

where

LM3242

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SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015

Typical Application (continued)

8.2.1 Design Requirements

For typical step-down DC-DC applications, use the parameters listed in Table 2.

Table 2. Design Parameters

DESIGN PARAMETER

EXAMPLE VALUE

Minimum input voltage

2.7 V

Minimum output voltage

0.4 V

Output current

0 to 750 mA

Switching frequency

6 MHz (typical)

8.2.2 Detailed Design Procedure

8.2.2.1 Inductor Selection

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

current ripple is small enough to achieve the desired output voltage ripple. Different manufacturers follow

different saturation current rating specifications, so attention must be given to details. Saturation current ratings

are typically specified at 25°C so ratings over the ambient temperature of application should be requested from

manufacturer.

ambient temperature range. Shielded inductors radiate less noise and are preferred. There are two methods to

choose the inductor saturation current rating:

8.2.2.1.1

Method 1

The saturation current must be greater than the sum of the maximum load current and the worst-case average-

to-peak inductor current. This can be written as:

where

•

•

•

•

L minimum inductor value including worst-case tolerances (30% drop can be considered for Method 1)

•

F: minimum switching frequency (5.7 MHz)

•

(2)

8.2.2.1.2

Method 2

A more conservative and recommended approach is to choose an inductor that can handle the maximum current

limit of 1600 mA.

The resistance of the inductor must be less than approximately 0.1

Ω for good efficiency. Table 3 lists suggested

inductors and suppliers.

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