©

§

2 x L

©

§

x

x

1

f

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where

LM3242

www.ti.com

SNOSB48D – OCTOBER 2011 – REVISED MARCH 2013

APPLICATION INFORMATION

Setting the Output Voltage

The LM3242 features a pin-controlled adjustable output voltage to eliminate the need for external feedback

resistors. It can be programmed for an output voltage from 0.4V to 3.6V by setting the voltage on the VCON pin,

as in the following formula:

(1)

When VCON is between 0.16V and 1.44V, the output voltage will follow proportionally by 2.5 times of VCON.

“Low VCON Voltage vs. Output Voltage” for details. This curve exhibits the characteristics of a typical part, and

the performance cannot be ensured as there could be a part-to-part variation for output voltages less than 0.4V.

operation.

FB

Typically the FB pin is connected to VOUT for regulating the output voltage maximum of 3.6V.

Inductor Selection

There are two main considerations when choosing an inductor; the inductor should 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 should be preferred. There are two

methods to choose the inductor saturation current rating.

Method 1:

The saturation current should 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)

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Product Folder Links: LM3242