LT3493EDCB-PBF Ver la hoja de datos (PDF) - Linear Technology

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LT3493EDCB-PBF

1.2A, 750kHz Step-Down Switching Regulator in 2mm × 3mm DFN

Linear Technology 

LT3493

OPERATION (Refer to Block Diagram)

The LT3493 is a constant frequency, current mode step-

down regulator. A 750kHz 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.

An internal regulator provides power to the control circuitry.

This regulator includes an undervoltage lockout to prevent

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

used to place the LT3493 in shutdown, disconnecting 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 LT3493’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.

3493fb

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