LTM4607 datasheet(9/26 Pages) LINER

9 / 26 page

LTM8055

8055fb

For more information www.linear.com/LTM8055

OPERATION

The LTM8055 is a standalone nonisolated buck-boost

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

ogy allows the LTM8055 to regulate its output voltage for

input voltages both above and below the magnitude of the

output. The maximum output current depends upon the

inputvoltage.Higherinputvoltagesyieldhighermaximum

output current.

This converter provides a precisely regulated output volt-

age programmable via an external resistor divider from

1.2V to 36V. The input voltage range is 5V to 36V, but the

LTM8055 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 LTM8055 contains a current mode controller, power

switching elements, power inductor and a modest amount

of input and output capacitance. The LTM8055 is a fixed

frequency PWM regulator. The switching frequency is set

by connecting the appropriate resistor value from the RT

pin to GND.

The output voltage of the LTM8055 is set by connecting

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

In addition to regulating its output voltage, the LTM8055

is equipped with average current 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 LTM8055 to accurately regulate its output current to

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

When the resistor is present, the IOUTMON pin reflects the

output current flowing through VOUT.

In general, the LTM8055 should be used with an output

sense resistor to limit the maximum output current, as

buck-boost regulators are capable of delivering large

currents when the output voltage is lower than the input,

if demanded.

Furthermore, while the LTM8055 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

LTM8055 against output overload or short-circuit.

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

the maximum output current. Drive CTL to about 50mV

to stop switching. The current flowing through the sense

resistorisreflectedbytheoutputvoltageoftheIOUTMONpin.

Driving the SYNC pin will synchronize the LTM8055 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 LTM8055

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 LTM8055 in shutdown, disconnecting

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

The LTM8055 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.

LTM4607 Datasheet(PDF) 9 Page - Linear Technology

LTM4607 Datasheet(HTML) 9 Page - Linear Technology

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

Datasheet Download

Link URL