NCV2574DW-ADJR2 データシートの表示（PDF） - ON Semiconductor

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NCV2574DW-ADJR2

0.5 A, Adjustable Output Voltage, Step-Down Switching Regulator

ON Semiconductor 

7.0 - 40 V

Unregulated

DC Input

LM2574, NCV2574

Fixed Output Voltage Versions

Vin

1 (12)

4

Cin

22 mF

LM2574

Feedback

(3)

1

Fixed Output

Output

(14)

7

Pwr 2 Sig 3 ON/OFF

Gnd Gnd

(5)

(6)

(4)

L1

330 mH

D1

1N5819

Vout

Cout

Load

220 mF

7.0 V - 40 V

Unregulated

DC Input

Cin −

Cout −

D1 −

L1 −

R1 −

R2 −

22 mF, 60 V, Aluminium Electrolytic

220 mF, 25 V, Aluminium Electrolytic

Schottky, 1N5819

330 mH, (For 5.0 Vin, 3.3 Vout, use 100 mH)

2.0 k, 0.1%

6.12 k, 0.1%

Adjustable Output Voltage Versions

Vin

1 (12)

4

Cin

22 mF

Feedback

(3)

1

LM2574

Adjustable

Output

(14)

7

Pwr 2 Sig 3 ON/OFF

Gnd Gnd

(5)

(6)

(4)

L1

330 mH

D1

1N5819

Cout

220 mF

ǒ Ǔ Vout + Vref 

1.0

) 

R2

R1

ǒ Ǔ R2 + R1

Vout

Vref

 – 1.0

Where Vref = 1.23 V, R1

between 1.0 kW and 5.0 kW

NOTE: Pin numbers in ( ) are for the SO−16W package.

Figure 16. Test Circuit and Layout Guidelines

R2

6.12 k

R1

2.0 k

Vout

5.0 V

Load

PCB LAYOUT GUIDELINES

As in any switching regulator, the layout of the printed

circuit board is very important. Rapidly switching currents

associated with wiring inductance, stray capacitance and

parasitic inductance of the printed circuit board traces can

generate voltage transients which can generate

electromagnetic interferences (EMI) and affect the desired

operation. As indicated in the Figure 16, to minimize

inductance and ground loops, the length of the leads

indicated by heavy lines should be kept as short as possible.

For best results, single−point grounding (as indicated) or

ground plane construction should be used.

On the other hand, the PCB area connected to the Pin 7

(emitter of the internal switch) of the LM2574 should be

kept to a minimum in order to minimize coupling to sensitive

circuitry.

Another sensitive part of the circuit is the feedback. It is

important to keep the sensitive feedback wiring short. To

assure this, physically locate the programming resistors near

to the regulator, when using the adjustable version of the

LM2574 regulator.

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