LTM8024 datasheet(15/28 Pages) AD

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LTM8080

Rev. 0

For more information www.analog.com

The LTM8080 is a 40VIN, dual 500mA or single 1A ultralow

noise, ultrahigh PSRR µModule regulator. LTM8080 has

cascaded architecture with a 40VIN step-down Silent

Switcher regulator and dual high-performance low-drop-

out linear regulators. The dual LDOs feature ADI’s ultralow

noise and ultrahigh PSRR architecture for powering

noise- sensitive applications. The LTM8080 is an inte-

grated solution of a switching regulator and two LDOs

which offers both advantages while maintaining a small

size and significantly reduced PCB layout sensitivity.

The package includes the controllers, power switches,

inductors, and support components. Operating over a

wide input voltage range, the LTM8080 supports a switch-

ing frequency range of 200kHz to 2.2MHz and a wide

output voltage range of 0V to 8V.

The LTM8080 has a built-in voltage tracking function that

automatically sets VBUS to 1V higher than the VSNS1 or

sets VBUS to 2.5V, whichever is higher, to achieve the best

noise performance and minimized power dissipation.

Switching Regulator

The front-end switching regulator is a nonisolated step-

down switching DC/DC power supply that can deliver up

to 1.5A continuous current. The internal operating tem-

perature determines the continuous current. If VSNS1 is

higher than 1.5V, VBUS is regulated to be 1V higher than

VSNS1; if VSNS1 is lower than 1.5V, VBUS is set to 2.5V. The

input voltage range is 3.5V to 40V. Given that the switch-

ing regulator is a step-down converter ensure that the

input voltage is high enough to support the desired output

voltage and load current. See simplified Block Diagram.

The front-end switching regulator contains a current mode

controller, power switching elements, a power inductor,

and a modest input and output capacitance. The switching

regulator is a fixed-frequency PWM regulator. The switch-

ing frequency is set by simply connecting the appropriate

resistor value from the RT pin to GND.

Use the RUN pin to place the switching regulator in shut-

down, reducing the input current to a few microamps.

To enhance efficiency, tie the SYNC pin to GND, so the

switching regulator automatically switches 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 to just a

few microamps.

The oscillator reduces the switching regulator’s operating

frequency when the voltage at the internal FB pin is low.

This frequency foldback helps to control the output cur-

rent during start-up and overload.

A Soft-start is implemented by generating a voltage ramp

at the SS pin using an external capacitor that is charged

by an constant internal current.

The switching regulator is equipped with a thermal

shutdown that inhibits power switching at high junction

temperatures. The activation threshold of this function

is above the maximum temperature rating to avoid inter-

fering with regular operation, so prolonged or repet-

itive operation under a condition in which the thermal

shutdown activates may damage or impair the device’s

reliability.

Linear Regulators

The back-end linear regulators are high-performance

low dropout linear regulators featuring ADI’s ultralow

noise (2nV/√Hz at 10kHz) and ultrahigh PSRR (76dB at

1MHz) architecture for powering noise-sensitive applica-

tions. Designed as a precision current source followed

by a high-performance rail-to-rail voltage buffer, the LDO

outputs can be easily paralleled to reduce noise further,

increase output current, and spread heat on the PCB. The

device additionally features fast start-up capability and

programmable power good.

The LDOs are easy to use and incorporate all the protec-

tion features expected in high-performance regulators.

Included are short-circuit protection, safe operating area

protection, reverse-battery protection, reverse-current

protection, and thermal shutdown with hysteresis.

The VOUT1 LDO incorporates a VIOC tracking function to

control the front-end switching regulator to maintain a 1V

constant voltage across the LDO VOUT1 and minimizing

power dissipation.

OPERATION

LTM8024 Datasheet(PDF) 15 Page - Analog Devices

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