lt3493edcb-3 Linear Technology Corporation, lt3493edcb-3 Datasheet - Page 7

• Manufacturer Part Number: lt3493edcb-3
• Description: 1.2a, 750khz Step-down Switching Regulator In 2mm X 3mm Dfn
• Manufacturer: Linear Technology Corporation

OPERATIO
The LT3493-3 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 V
this current reaches a level determined by the voltage at
V
an external resistor divider tied to the FB pin and servos the
V
current is delivered to the output; if it decreases, less
current is delivered. An active clamp (not shown) on the V
node provides current limit. The V
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.
C
C
. An error amplifier measures the output voltage through
node. If the error amplifier’s output increases, more
IN
and SW pins, turning the switch off when
U
(Refer to Block Diagram)
C
node is also clamped
C
An internal regulator provides power to the control cir-
cuitry. This regulator includes an undervoltage lockout to
prevent switching when V
pin is used to place the LT3493-3 in shutdown, discon-
necting 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 LT3493-3’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.
IN
is less than 6.8V. The SHDN
LT3493-3
3493-3f
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