LM2576TV-3.3 데이터 시트보기 (PDF) - ON Semiconductor

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LM2576TV-3.3

3.0 A, 15 V, Step−Down Switching Regulator

ON Semiconductor 

LM2576

Procedure (Fixed Output Voltage Version) In order to simplify the switching regulator design, a step−by−step

design procedure and some examples are provided.

Procedure

Example

Given Parameters:

Vout = Regulated Output Voltage (3.3 V, 5.0 V, 12 V or 15 V)

Vin(max) = Maximum Input Voltage

ILoad(max) = Maximum Load Current

1. Controller IC Selection

According to the required input voltage, output voltage and

current, select the appropriate type of the controller IC output

voltage version.

Given Parameters:

Vout = 5.0 V

Vin(max) = 15 V

ILoad(max) = 3.0 A

1. Controller IC Selection

According to the required input voltage, output voltage,

current polarity and current value, use the LM2576−5

controller IC

2. Input Capacitor Selection (Cin)

To prevent large voltage transients from appearing at the input

and for stable operation of the converter, an aluminium or

tantalum electrolytic bypass capacitor is needed between the

input pin +Vin and ground pin GND. This capacitor should be

located close to the IC using short leads. This capacitor should

have a low ESR (Equivalent Series Resistance) value.

2. Input Capacitor Selection (Cin)

A 100 mF, 25 V aluminium electrolytic capacitor located near

to the input and ground pins provides sufficient bypassing.

3. Catch Diode Selection (D1)

A. Since the diode maximum peak current exceeds the

regulator maximum load current the catch diode current

rating must be at least 1.2 times greater than the maximum

load current. For a robust design the diode should have a

current rating equal to the maximum current limit of the

LM2576 to be able to withstand a continuous output short

B. The reverse voltage rating of the diode should be at least

1.25 times the maximum input voltage.

3. Catch Diode Selection (D1)

A. For this example the current rating of the diode is 3.0 A.

B. Use a 20 V 1N5820 Schottky diode, or any of the

suggested fast recovery diodes shown in Table 1.

4. Inductor Selection (L1)

A. According to the required working conditions, select the

correct inductor value using the selection guide from

Figures 18 to 22.

B. From the appropriate inductor selection guide, identify the

inductance region intersected by the Maximum Input

Voltage line and the Maximum Load Current line. Each

region is identified by an inductance value and an inductor

code.

C. Select an appropriate inductor from the several different

manufacturers part numbers listed in Table 2.

The designer must realize that the inductor current rating

must be higher than the maximum peak current flowing

through the inductor. This maximum peak current can be

calculated as follows:

Ip(max)

+

ILoad(max)

)

ǒVin–VoutǓ

2L

ton

where ton is the “on” time of the power switch and

ton

+

Vout

Vin

x

1.0

fosc

For additional information about the inductor, see the

inductor section in the “Application Hints” section of

this data sheet.

4. Inductor Selection (L1)

A. Use the inductor selection guide shown in Figures 19.

B. From the selection guide, the inductance area intersected

by the 15 V line and 3.0 A line is L100.

C. Inductor value required is 100 mH. From Table 2, choose

an inductor from any of the listed manufacturers.

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