LTM8080 datasheet(13/32 Pages) AD

13 / 32 page

LTM4703

Rev. 0

For more information www.analog.com

The LTM4703 is a standalone, nonisolated step-down

switching DC/DC power supply that can deliver up to 12A.

The continuous current is determined by the internal oper-

ating temperature. It provides a precisely regulated output

voltage programmable through one external resistor from

0.3V to 6V. The input voltage range is 3V to 16V. Given

that the LTM4703 is a step-down converter, ensure that

the input voltage is high enough to support the desired

output voltage and the load current. See the simplified

Block Diagram.

The LTM4703 contains a current mode controller, power

switching elements, a power inductor, and a modest

amount of input and output capacitance. The LTM4703

is a fixed-frequency PWM regulator. The switching

frequency is set by simply connecting the appropriate

resistor value from the RT pin to the GND.

An internal regulator provides power to the control

circuitry. To improve efficiency across all loads, supply

current to the control circuitry can be sourced from the

SVIN pin when it is biased at 3V or above, instead of

connecting SVIN to VIN. If the RUN pin is below 0.4V,

the LTM4703 is shutdown, and draws 55µA from the

input. When the RUN pin rises above 1.32V (typical), the

LTM4703 becomes active.

To enhance efficiency at light load, the LTM4703 auto-

matically operates in pulse-skipping mode (PSM) in light

load situations. The SYNC pin is connected low for PSM

operation and connected to INTVCC, or to a voltage higher

than 3V for forced continuous mode (FCM). If a clock

is applied to the SYNC pin, the part synchronizes to an

external clock frequency and it operates in FCM.

The LTM4703 can operate in FCM for fast transient

response and full-frequency operation over a wide load

range. When in FCM, the oscillator operates continuously,

and positive SW transitions are aligned to the clock. A

negative inductor current is allowed. The LTM4703 can

sink current from the output and return this charge

to the input in this mode, improving the load step

transient response.

The LTM4703 incorporates fast start-up circuitry, which

allows the part to start-up at a short time while using a

larger value SET pin capacitor for ultralow-noise appli-

cations. See the Applications Information section for

more details.

The LTM4703 contains a power good comparator

that trips when the PGSET pin is between 462.5mV

and 537.5mV, 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 SVIN is above 3V. If SVIN is above

3V and RUN is low, PG remains low.

The LTM4703 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. Therefore,

prolonged or repetitive operation under a condition in

which the thermal shutdown activates may damage or

impair the reliability of the device.

Two or more LTM4703 devices may be operated in parallel

to produce higher currents.

OPERATION

LTM8080 датащи(PDF) 13 Page - Analog Devices

LTM8080 датащи(HTML) 13 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

датащи скачать

ссылки URL