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LTM8025 Datasheet(PDF) 9 Page - Linear Technology

Part No. LTM8025
Description  36V, 3A Step-Down Module Regulator
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Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
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LTM8025 Datasheet(HTML) 9 Page - Linear Technology

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LTM8025
9
8025fc
For more information www.linear.com/LTM8025
block DiagraM
operaTion
The LTM8025 is a standalone nonisolated step-down
switching DC/DC power supply that can deliver up to 3A of
outputcurrent.Thismoduleprovidesapreciselyregulated
output voltage programmable via one external resistor
from 0.8V to 25V. The input voltage range is 3.6V to 36V.
Given that the LTM8025 is a step-down converter, make
sure that the input voltage is high enough to support the
desired output voltage and load current.
As shown in the Block Diagram, the LTM8025 contains a
current mode controller, power switching element, power
inductor, power Schottky diode and a modest amount of
input and output capacitance. The LTM8025 is a fixed
frequency PWM regulator. The switching frequency is set
by simply connecting the appropriate resistor value from
the RT pin to GND.
Aninternalregulatorprovidespowertothecontrolcircuitry.
The bias regulator normally draws power from the VIN
pin, but if the BIAS pin is connected to an external volt-
age higher than 2.8V, bias power will be drawn from the
external source (typically the regulated output voltage).
This improves efficiency. The RUN/SS pin is used to place
the LTM8025 in shutdown, disconnecting the output and
reducing the input current to less than 1μA.
To further optimize efficiency, the LTM8025 automatically
switches to Burst Mode® operation in light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down reducing the input supply
current to 50μA in a typical application.
The oscillator reduces the LTM8025’s operating frequency
when the voltage at the ADJ pin is low. This frequency
foldback helps to control the output current during start-
up and overload.
The LTM8025 contains a power good comparator which
trips when the ADJ pin is at roughly 90% of its regulated
value. The PGOOD output is an open-collector transistor
that is off when the output is in regulation, allowing an
externalresistortopullthePGOODpinhigh.Powergoodis
valid when the LTM8025 is enabled and VIN is above 3.6V.
The LTM8025 is equipped with a thermal shutdown that
will inhibit power switching at high junction tempera-
tures. The activation threshold of this function, however,
is above 125°C to avoid interfering with normal operation.
Thus, prolonged or repetitive operation under a condition
in which the thermal shutdown activates may damage or
impair the reliability of the device.
8025 BD
VIN
8.2µH
4.4µF
0.2µF
CURRENT
MODE
CONTROLLER
RUN/SS
SHARE
SYNC
AUX
BIAS
GND
RT
ADJ
PGOOD
VOUT
15pF
499k


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