LTM4607 datasheet(10/28 Pages) LINER

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LTM8056

8056fa

For more information www.linear.com/LTM8056

OPERATION

The LTM8056 is a standalone nonisolated buck-boost

switching DC/DC power supply. The buck-boost topol-

ogy allows the LTM8056 to regulate its output voltage

for input voltages both above and below the magnitude

of the output, and the maximum output current depends

upon the input voltage. Higher input voltages yield higher

maximum output current.

This converter provides a precisely regulated output volt-

age programmable via an external resistor divider from

1.2V to 48V. The input voltage range is 5V to 58V, but the

LTM8056 may be operated at lower input voltages if SVIN

is powered by a voltage source above 5V. A simplified

block diagram is given on the previous page.

The LTM8056 contains a current mode controller, power

switching elements, power inductor and a modest amount

of input and output capacitance. The LTM8056 is a fixed

frequency PWM regulator. The switching frequency is set

by connecting the appropriate resistor value from the RT

pin to GND.

TheoutputvoltageoftheLTM8056issetbyconnectingthe

FB pin to a resistor divider between the output and GND.

In addition to regulating its output voltage, the LTM8056

is equipped with averagecurrent control loops for both the

input and output. Add a current sense resistor between IIN

and VIN to limit the input current below some maximum

value. The IINMON pin reflects the current flowing though

the sense resistor between IIN and VIN.

A current sense resistor between VOUT and IOUT allows

the LTM8056 to accurately regulate its output current to

a maximum value set by the value of the sense resistor.

In general, the LTM8056 should be used with an output

sense resistor to limit the maximum output current, as

buck-boost regulators are capable of delivering large cur-

rents when the output voltage is lower than the input, if

demanded.

Furthermore, while the LTM8056 does not require an

output sense resistor to operate, it uses information from

the sense resistor to optimize its performance. If an out-

put sense resistor is not used, the efficiency or output

ripple may degrade, especially if the current through the

integrated inductor is discontinuous. In some cases, an

output sense resistor is required to adequately protect the

LTM8056 against output overload or short-circuit.

A voltage less than 1.2V applied to the CTL pin reduces

the maximum output current if an output current sense

resistor is used. Drive CTL to less than about 50mV to stop

switching. The current flowing through the sense resistor

is reflected by the output voltage of the IOUTMON pin.

Driving the SYNC pin will synchronize the LTM8056 to an

external clock source. The CLKOUT pin sources a signal

that is the same frequency but approximately 180° out of

phase with the internal oscillator.

If more output current is required than a single LTM8056

can provide, multiple devices may be operated in parallel.

Refer to the Parallel Operation section of Applications

Information for more details.

Aninternalregulatorprovidespowertothecontrolcircuitry

and the gate driver to the power MOSFETs. This internal

regulator draws power from the SVIN pin. The RUN pin is

used to place the LTM8056 in shutdown, disconnecting

the output and reducing the input current to less than 1μA.

The LTM8056 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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