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LT1616

BLOCK DIAGRA

DRIVER

OSC

SLOPE

COMP

FREQUENCY

FOLDBACK

INT REG

AND

UVLO

1.25V

1616BD

GND

VIN

SHDN

BOOST

OPERATIO

The LT1616 is a constant frequency, current mode Buck

regulator. The 1.4MHz oscillator enables an RS flip-flop,

turning on the internal 600mA power switch Q1. An ampli-

fier and comparator monitor the current flowing between

the VINandSWpins,turningtheswitchoffwhenthiscurrent

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. This amplifier servos the

switch current to regulate the FB pin voltage to 1.25V. An

active clamp on the VC node provides current limit.

An internal regulator provides power to the control cir-

cuitry. This regulator includes an undervoltage lockout to

prevent switching when VIN is less than ~ 3.5V. The

(Refer to Block Diagram)

SHDN pin is used to place the LT1616 in shutdown,

disconnecting the output and reducing the input current

to less than 1

µA.

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 LT1616’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.

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