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LM2594, LM2594HV

SNVS118D – DECEMBER 1999 – REVISED MAY 2016

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8 Detailed Description

8.1 Overview

with a wide input voltage range from 45 V to up to 60 V for a HV version. The regulator is capable of delivering

up to 0.5-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 Delayed Start-Up

The circuit in Figure 14 uses the ON/OFF pin to provide a time delay between the time the input voltage is

applied and the time the output voltage comes up (only the circuitry pertaining to the delayed start-up is shown).

As the input voltage rises, the charging of capacitor C1 pulls the ON/OFF pin high, keeping the regulator off.

the ON/OFF pin (maximum of 25 V), reduces power supply noise sensitivity, and also limits the capacitor, C1,

discharge current. When high input ripple voltage exists, avoid long delay time, because this ripple can be

coupled into the ON/OFF pin and cause problems.

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

current it can deliver. It allows the input voltage to rise to a higher voltage before the regulator starts operating.

Buck regulators require less input current at higher input voltages.