LM2594 Просмотр технического описания (PDF) - ON Semiconductor

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производитель

LM2594

0.5 A, Step-Down Switching Regulator

ON Semiconductor 

LM2594

PROCEDURE (ADJUSTABLE OUTPUT VERSION: LM2594)

Procedure

Example

Given Parameters:

Vout = Regulated Output Voltage

Vin(max) = Maximum DC Input Voltage

ILoad(max) = Maximum Load Current

1. Programming Output Voltage

To select the right programming resistor R1 and R2 value (see

Figure 1) use the following formula:

ǒ Ǔ Vout + Vref

1.0 )

R2

R1

where Vref = 1.23 V

Resistor R1 can be between 1.0 k and 5.0 kW. (For best

temperature coefficient and stability with time, use 1% metal

film resistors).

ǒ Ǔ R2 + R1 Vout * 1.0

Vref

Given Parameters:

Vout = 5.0 V

Vin(max) = 12 V

ILoad(max) = 0.5 A

1. Programming Output Voltage (selecting R1 and R2)

Select R1 and R2:

ǒ Ǔ Vout

+

1.23

1.0 )

R2

R1

Select R1 = 1.0 kW

ǒ Ǔ ǒ Ǔ R2 + R1

Vout

Vref

*

1.0

+

5V

1.23 V * 1.0

R2 = 3.0 kW, choose a 3.0k metal film resistor.

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 68 mF, 50 V aluminium electrolytic capacitor located near

the input and ground pin provides sufficient bypassing.

For additional information see input capacitor section in the

“Application Information” section of this data sheet.

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

LM2594 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, a 1.0 A current rating is adequate.

B. For Vin = 12 V use a 20 V 1N5817 Schottky diode or

any suggested fast recovery diode in the Table 2.

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