LM2596 データシートの表示（PDF） - Estek Electronics Co. Ltd

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LM2596

3A Step-Down Voltage Regulator

Estek Electronics Co. Ltd 

LM2596

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable Output Voltage Version)

R 2  R 1( VOUT 

1) VREF

2. Inductor Selection (L1)

2. Inductor Selection (L1)

Ath.eCfoalllcouwlaitnegthfoerimnudluac:tor Volt •microsecond constant ET (Vµs), from A(E. CTa)l,culate the inductor Volt  microsecond constant

ET (VINVOUTVSAT)

VVIN

VD

VSAT VD

 1000

kHz

 s)

150

where VSAT = internal switch saturation voltage = 1.16V

and VD = diode forward voltage drop = 0.5V

B. Use the ET value from the previous formula and match it with the

ET 

28(

ET (

 20

.1

)1

20 0

28 5. 1 0

1000

 (V

s)

150

1 6. 5.

.6 84) 





.205

 .3 

ET number on the vertical axis of the Inductor Value Selection Guide

shown in Figure 7.

C. on the horizontal axis, select the maximum load current.

C.

D. Identify the inductance region intersected by the ET value and the

Maximum Load Current value. Each region is identified by an

inductance value and an inductor code (LXX).

E. Select an appropriate inductor from the four manufacturer’s part

numbers listed in Figure 8.

D. From the inductor value selection guide shown in Figure 7, the

inductance region intersected by the 34 (Vµs) horizontal line and

the 3A vertical line is 47 µH, and the inductor code is L39.

E. From the table in Figure 8, locate line L39, and select an

inductor part number from the list of manufacturers part numbers.

3. Output Capacitor Selection (COUT)

A. In the majority of applications, low ESR electrolytic or solid tantalum

capacitors between 82 µF and 820 µF provide the best results. This capacitor

should be located close to the IC using short capacitor leads and short copper

traces. Do not use capacitors larger than 820 µF.

B. To simplify the capacitor selection procedure, refer to the quick

design table shown in Figure 3. This table contains different output

voltages, and lists various output capacitors that will provide the best

design solutions.

3. Output Capacitor SeIection (COUT)

B. From the quick design table shown in Figure 3, locate the output voltage

column. From that column, locate the output voltage closest to the output

voltage in your application. In this example, select the 24V line. Under the

output capacitor section, select a capacitor from the list of through hole

electrolytic or surface mount tantalum types from four different capacitor

manufacturers. It is recommended that both the manufacturers and the

manufacturers series that are listed in the table be used.

In this example, through hole aluminum electrolytic capacitors from

several different manufacturers are available.

220 µF/35V Panasonic HFQ Series

150 µF/35V Nichicon PL Series

C. The capacitor voltage rating should be at least 1.5 times greater than C. For a 20V output, a capacitor rating of at least 30V or more is

the output voltage, and often much higher voltage ratings are needed to needed. In this example, either a 35V or 50V capacitor would

satisfy the low ESR requirements needed for low output ripple voltage. work. A 35V rating was chosen, although a 50V rating could also

be used if a lower output ripple voltage is needed.

Other manufacturers or other types of capacitors may also be used,

provided the capacitor specifications (especially the 100 kHz

ESR) closely match the types listed in the table. Refer to the

capacitor manufacturers data sheet for this information.

4. Feedforward Capacitor (CFF ) (See Figure 1)

For output voltages greater than approximately 10V, an additional

capacitor is required. The compensation capacitor is typically between

100 pF and 33 nF, and is wired in parallel with the output voltage

setting resistor, R2. It provides additional stability for high output

voltages, low input-output voltages, and/or very low ESR output

capacitors, such as solid tantalum capacitors.

4. Feedforward Capacitor (CFF )

The table shown in Figure 3 contains feed forward capacitor

values for various output voltages. In this example, a 560 pF

capacitor is needed.

 CFF

31R 12103

This capacitor type can be ceramic, plastic, silver mica, etc. (Because of

the unstable characteristics of ceramic capacitors made with Z5U

material, they are not recommended.)

BEIJING ESTEK ELECTRONICS CO.,LTD

10

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