LM2598 datasheet(34/47 Pages) TI1

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LM2598

SNVS125D – MARCH 1998 – REVISED MAY 2016

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Select a value for R1 with Equation 2 between 240 Ω and 1.5 kΩ. The lower resistor values minimize noise

pickup in the sensitive feedback pin. (For the lowest temperature coefficient and the best stability with time, use

1% metal film resistors.)

(2)

Select R1 with Equation 3 to be 1 kΩ, 1%. Solve for R2.

(3)

R2 = 1k (16.26 – 1) = 15.26k, closest 1% value is 15.4 kΩ.

R2 = 15.4 kΩ.

9.2.2.2.2

Inductor Selection (L1)

1. Calculate the inductor Volt • microsecond constant E • T (V • μs) with Equation 4.

where

•

VSAT = internal switch saturation voltage = 1 V

•

VD = diode forward voltage drop = 0.5 V

(4)

Calculate the inductor Volt • microsecond constant (E • T) with Equation 5.

(5)

2. Use the E • T value from the previous formula and match it with the E • T number on the vertical axis of the

see the inductor selection graphs in Figure 35 through Figure 38.

E • T = 34.8 (V • μs)

3. On the horizontal axis, select the maximum load current.

ILOAD(max) = 1 A

4. 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).

From the inductor selection graphs in Figure 35 through Figure 38, the inductance region intersected by the

35 (V • μs) horizontal line and the 1-A vertical line is 100 μH, and the inductor code is L29.

5. Select an appropriate inductor from the four manufacturer's part numbers listed in Table 2.

From the table in Table 2, locate line L29, and select an inductor part number from the list of manufacturers'

part numbers.

9.2.2.2.3

Output Capacitor Selection (COUT)

1. In the majority of applications, low ESR electrolytic or solid tantalum capacitors between 82 μF and 220 μF

provide the best results. This capacitor must be located close to the IC using short capacitor leads and short

copper traces. Do not use capacitors larger than 220 μF. For additional information, see Output Capacitor

(COUT).

2. To simplify the capacitor selection procedure, see Table 1 for a quick design guide. This table contains

different output voltages, and lists various output capacitors that provide the best design solutions.

From Table 1, 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 24-V line. Under the Output Capacitor (COUT)

section, select a capacitor from the list of through hole electrolytic or surface mount tantalum types from four

different capacitor manufacturers. TI recommends that both the manufacturers and the manufacturers series

that are listed in Table 1 be used.

In this example, through hole aluminum electrolytic capacitors from several different manufacturers are

available:

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