LT3503 Просмотр технического описания (PDF) - Linear Technology

Номер в каталоге

Компоненты Описание

производитель

LT3503

1A, 2.2MHz Step-Down Switching Regulator in 2mm × 3mm DFN

Linear Technology 

U

OPERATIO (Refer to Block Diagram)

The LT3503 is a constant frequency, current mode step-

down regulator. A 2.2MHz oscillator enables an RS flip-

flop, turning on the internal 1.75A power switch Q1. An

amplifier and comparator monitor the current flowing

between the VIN and SW pins, turning the switch off when

this current reaches a level determined by the voltage at

VC. An error amplifier measures the output voltage through

an external resistor divider tied to the FB pin and servos the

VC node. If the error amplifier’s output increases, more

current is delivered to the output; if it decreases, less

current is delivered. An active clamp (not shown) on the VC

node provides current limit. The VC node is also clamped

to the voltage on the SHDN pin; soft-start is implemented

by generating a voltage ramp at the SHDN pin using an

external resistor and capacitor.

LT3503

An internal regulator provides power to the control cir-

cuitry. This regulator includes an undervoltage lockout to

prevent switching when VIN is less than ~3.4V. The SHDN

pin is used to place the LT3503 in shutdown, disconnect-

ing the output and reducing the input current to less than

2µA.

The switch driver operates from either the input or from

the BOOST pin. An external capacitor and diode are used

to generate a voltage at the BOOST pin that is higher than

the input supply. This allows the driver to fully saturate the

internal bipolar NPN power switch for efficient operation.

The oscillator reduces the LT3503’s operating frequency

when the voltage at the FB pin is low. This frequency

foldback helps to control the output current during start-

up and overload.

3503f

7

Share Link: