ML4865 Просмотр технического описания (PDF) - Fairchild Semiconductor

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ML4865

High Voltage High Current Boost Regulator

Fairchild Semiconductor 

ML4865

PRODUCT SPECIFICATION

Design Example

In order to design a boost converter using the ML4865, it is

necessary to define the values of a few parameters. For this

example, assume the following design parameters:

VIN = 4.75 to 5.25V

VOUT = 12V

IOUT(MAX) = 150mA

Shutdown required

First, it must be determined whether the ML4865 is capable

of delivering the output current without an external Schottky

rectifier. This is done using Equation 1:

IOUT (MAX)

≅

VIN

VOUT

× ((0.05 × VIN

+ 0.4

× 0.65

IOUT (MAX)

≅

5.25

12

×

((0.05

×

5.25

+ 0.4

× 0.65 = 188mA

Next, select an inductor. As previously mentioned, the rec-

ommended inductance is 22µH. Make sure that the peak cur-

rent rating of the inductor is at least 1.5A, and that the DC

resistance of the inductor is in the range of 110 to 220mΩ. A

Sumida CD75-220 meets these requirements.

Finally, the value of the output capacitor is determined using

Equation 2:

COUT

=

10 × L

VOUT

=

10 × 22µH

12V

= 18.3µF

The closest standard value would be a 22µF capacitor with

an ESR rating of 200mΩ. An AVX TPSD226M025R0200

would be a good choice.

As mentioned previously, the use of an input supply bypass

capacitor is highly recommended. Since the output capaci-

tance meets the minimum input capacitance recommended it

can also be used for the input.

8

REV. 1.0.2 8/10/01

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