LTM8053 datasheet(14/28 Pages) LINER

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LTM8053

8053fc

For more information www.linear.com/LTM8053

OPERATION

The LTM8053 is a stand-alone non-isolated step-down

switching DC/DC power supply that can deliver up to

6A. The continuous current is determined by the internal

operating temperature. It provides a precisely regulated

output voltage programmable via one external resistor

from 0.97V to 15V. The input voltage range is 3.4V to 40V.

Given that the LTM8053 is a step-down converter, make

sure that the input voltage is high enough to support the

desired output voltage and load current. A simplified Block

Diagram is given on the previous page.

The LTM8053 contains a current mode controller, power

switching elements, power inductor and a modest amount

of input and output capacitance. The LTM8053 is a fixed

frequency PWM regulator. The switching frequency is set

by simply connecting the appropriate resistor value from

the RT pin to GND.

An internal regulator provides power to the control cir-

cuitry. This bias regulator normally draws power from the

VIN pin, but if the BIAS pin is connected to an external

voltage higher than 3.2V, bias power is drawn from the

external source (typically the regulated output voltage).

This improves efficiency. The RUN pin is used to place

the LTM8053 in shutdown, disconnecting the output and

reducing the input current to a few A.

Toenhanceefficiency,theLTM8053automaticallyswitches

to Burst Mode operation in light or no load situations.

Between bursts, all circuitry associated with controlling

the output switch is shut down reducing the input supply

current.

TheoscillatorreducestheLTM8053’soperatingfrequency

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

back helps to control the output current during start-up

and overload.

The TR/SS node acts as an auxiliary input to the error

amplifier. The voltage at FB servos to the TR/SS voltage

until TR/SS goes about 0.97V. Soft-start is implemented

by generating a voltage ramp at the TR/SS pin using an

externalcapacitorwhichischargedbyaninternalconstant

current. Alternatively, driving the TR/SS pin with a signal

source or resistive network provides a tracking function.

Do not drive the TR/SS pin with a low impedance volt-

age source. See the Applications Information section for

more details.

The LTM8053 contains a power good comparator which

trips when the FB pin is between 0.89V and 1.05V, typical.

The PG output is an open-drain transistor that is off when

the output is in regulation, allowing an external resistor

to pull the PG pin high. The PG signal is valid when VIN

is above 3.4V. If VIN is above 3.4V and RUN is low, PG

will drive low.

The LTM8053 is equipped with a thermal shutdown that

inhibits power switching at high junction temperatures.

The activation threshold of this function is above 125°C

to avoid interfering with normal operation, so prolonged

or repetitive operation under a condition in which the

thermal shutdown activates may damage or impair the

reliability of the device.

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