MD3221N 查看數據表（PDF） - Unspecified

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MD3221N

DC-DC Converter Power IC

Unspecified 

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4 Selection of Primary Components and Pin Connections

The characteristics of the DC-DC converter are influenced by the IC itself, and also significantly by the

peripheral components of the circuit.

A well-designed circuit is necessary to make the most of the potential of the MD3221N. It is therefore necessary

to clarify the specifications of the required power supply, and to select components as follows.

● Standard Connection Diagram

+Vi

C1

+

G

C4

D1

C3

C7 C2

7

Vboot

18~21 VDD

24

VB

VOUT 11~14

6 VCC

32 S/S

1 R/C

MD3221N

OCL+ 25

OCL- 27

ampOUT 28

5 LC

Vref

2

amp- 29

ampIN 30

2.5V/3.3V 31

OSC GND P.GND1 P.GND2

3

4,26 8 16

C8

L1

+V0

R3

D2

C5

C6

+

G

◆Selecting the Output Choke Coil (inductor) (L1)

The choke coil has an important effect on power

supply performance. As a ripple current flows in the

inductor as shown in the diagram below, the

inductance should be selected to ensure that ΔI is

approximately 30% of the maximum output current

when the input voltage is at its maximum.

● Current Waveform in Output Choke Coil (L1)

ΔI

Io

0

L 1 ＝（Ｖ（i max）−VO）× VO ［H］

ΔI ×Ｖ（i max）× f

V（i max）：Maximum input voltage［V］

VO ：Output voltage［V］

ΔI ：30% of maximum output curren［t A］

f ：Oscillation frequency (100kHz or 300kHz［) Hz］

I O ：Maximum output curren［t A］

The inductor is generally selected on the basis

of the calculation, however in some cases the

nature of the product may require an inductor

which differs from the calculated value. An

inductor in which ΔI is between 20% and 40% of the

output current is recommended.

7

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