LM2598 datasheet(11/47 Pages) TI1

11 / 47 page

LM2598

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SNVS125D – MARCH 1998 – REVISED MAY 2016

Product Folder Links: LM2598

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8 Detailed Description

8.1 Overview

The LM2598 SIMPLE SWITCHER® regulator is an easy-to-use, nonsynchronous, step-down DC-DC converter

with a wide input voltage range up to 40 V. The regulator is capable of delivering up to 1-A DC load current with

excellent line and load regulation. These devices are available in fixed output voltages of 3.3-V, 5-V, 12-V and an

adjustable output version. The family requires few external components, and the pin arrangement was designed

for simple, optimum PCB layout.

8.2 Functional Block Diagram

8.3 Feature Description

8.3.1 SHUTDOWN and Soft-Start

The circuit shown in Figure 20 is a standard buck regulator with 24-VIN, 12-VOUT, 280-mA load, and using a

0.068-μF soft-start capacitor. The photo in Figure 18 and Figure 19 show the effects of Soft-start on the output

voltage, the input current, with, and without a soft-start capacitor. Figure 18 also shows the error flag output

going high when the output voltage reaches 95% of the nominal output voltage. The reduced input current

required at start-up is very evident when comparing the two photos. The Soft-start feature reduces the start-up

current from 1 A down to 240 mA, and delays and slows down the output voltage rise time.

This reduction in start-up current is useful in situations where the input power source is limited in the amount of

current it can deliver. In some applications Soft-start can be used to replace undervoltage lockout or delayed

start-up functions.

If a very slow output voltage ramp is desired, the Soft-start capacitor can be made much larger. Many seconds or

even minutes are possible.

If only the shutdown feature is required, the Soft-start capacitor can be eliminated.

LM2598 Datasheet(PDF) 11 Page - Texas Instruments