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LMR62421

www.ti.com

SNVS734A – OCTOBER 2011 – REVISED OCTOBER 2011

SOFT-START

reference voltage ramps to its nominal value of 1.255V in approximately 4.0ms. This forces the regulator output

to ramp up in a more linear and controlled fashion, which helps reduce inrush current.

INDUCTOR SELECTION

(1)

Therefore:

(2)

Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the

accurate duty cycle (See Calculating Efficiency and Junction Temperature for a detailed explanation). A more

accurate formula for calculating the conversion ratio is:

where

•

η equals the efficiency of the LMR62421 application.

(3)

The inductor value determines the input ripple current. Lower inductor values decrease the size of the inductor,

but increase the input ripple current. An increase in the inductor value will decrease the input ripple current.

Figure 15. Inductor Current

Copyright © 2011, Texas Instruments Incorporated

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