LM2596

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SNVS124C – NOVEMBER 1999 – REVISED APRIL 2013

PROCEDURE (Adjustable Output Voltage Version)

EXAMPLE (Adjustable Output Voltage Version)

2. Inductor Selection (L1)

2. Inductor Selection (L1)

A. Calculate the inductor Volt • microsecond constant E • T (V •

μs), A. Calculate the inductor Volt • microsecond constant

from the following formula:

(E • T),

where

(5)

•

B. E • T = 34.2 (V •

μs)

1.16V

•

(4)

D. From the inductor value selection guide shown in Figure 24, 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.

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

the E • T number on the vertical axis of the Inductor Value Selection E. From the table in Table 3, locate line L39, and select an inductor

Guide shown in Figure 24.

part number from the list of manufacturers part numbers.

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

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 Table 3.

tantalum capacitors between 82

μF and 820 μF provide the best B. From the quick design table shown in Table 2, locate the output

results. This capacitor should be located close to the IC using short voltage column. From that column, locate the output voltage closest

capacitor leads and short copper traces. Do not use capacitors to the output voltage in your application. In this example, select the

larger than 820

μF. For additional information, see section on 24V line. Under the OUTPUT CAPACITOR section, select a

output capacitors in Application Information section.

capacitor from the list of through hole electrolytic or surface mount

B. To simplify the capacitor selection procedure, refer to the quick tantalum types from four different capacitor manufacturers. It is

design table shown in Table 2. This table contains different output recommended that both the manufacturers and the manufacturers

voltages, and lists various output capacitors that will provide the best series that are listed in the table be used.

design solutions.

In this example, through hole aluminum electrolytic capacitors from

C. The capacitor voltage rating should be at least 1.5 times greater several different manufacturers are available.

than the output voltage, and often much higher voltage ratings are

220

μF/35V Panasonic HFQ Series

needed to satisfy the low ESR requirements needed for low output

150

μF/35V Nichicon PL Series

ripple voltage.

C. For a 20V output, a capacitor rating of at least 30V or more is

needed. In this example, either a 35V or 50V capacitor would 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.

For output voltages greater than approximately 10V, an additional The table shown in Table 2 contains feed forward capacitor values

capacitor is required. The compensation capacitor is typically for various output voltages. In this example, a 560 pF capacitor is

between 100 pF and 33 nF, and is wired in parallel with the output needed.

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

output capacitors, such as solid tantalum capacitors.

(6)

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.)

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