LTM8083 datasheet(9/24 Pages) AD

9 / 24 page

LTM8083

Rev. 0

For more information www.analog.com

OPERATION

The LTM8083 is a standalone non-isolated buck-boost

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

ogy allows the LTM8083 to regulate its output voltage

below or above input voltage. Maximum output current

is determined by the input voltage. Higher input voltages

yield higher maximum output current.

The LTM8083 contains ADI’s proprietary peak-buck peak-

boost current mode controller with four internal low resis-

tance N-channel DMOS switches, power inductor and a

modest amount of input and output capacitors.

This control scheme directly senses the inductor current

across the internal power switches and provides smooth

transition between buck region, buck-boost region and

boost region. A simplified block diagram is given on the

previous page. A precisely regulated output voltage is

programmable via an external resistor divider from 1V to

36V. The input voltage range is from 3V to 36V.

The LTM8083 is a fixed frequency PWM regulator. A resis-

tor from RT pin to GND sets the switching frequency from

300kHz to 2MHz, allowing applications to be optimized

for broad area and efficiency. Driving the SYNC pin will

synchronize the LTM8083 to an external clock source.

In addition to the voltage control loop, the LTM8083 is

equipped with average current control loop for the output.

Add a current sense resistor between ISP and ISN to limit

the output current below the maximum value set by the

CTRL pin. The ISMON pin reflects the current flowing

through the sense resistor.

A voltage less than 1.35V applied to the CTRL pin reduces

the maximum output current. The current flowing through

the sense resistor is reflected by the voltage of the ISMON

pin. Drive CTRL pin below 0.2V to stop switching.

At light load, the LTM8083 typically runs at its switching

frequency in discontinuous conduction mode. Both buck

and boost reverse current sense thresholds are set to be

zero, thus preventing any reverse current flowing from

the output to the input.

As the load becomes lower and lower, the LTM8083 may

run in pulse-skip mode, where the switches are held off

for multiple cycles (i.e., skipping pulses) to maintain the

regulation.

The LTM8083 enters shutdown mode with less than

0.9μA quiescent current when the EN/UVLO pin is below

its shutdown threshold (0.3V minimum).

The LTM8083 is equipped with a thermal shutdown that

inhibits operation when junction temperature is above

165°C. Prolonged or repetitive operation at junction tem-

perature higher than 125°C may damage or impair the

reliability of the device.

A low-ESL 10nF three-terminal capacitor is added on the

input side as well as output side, improving noise decou-

pling for better EMI performance. With a small filter and

Spread Spectrum function enabled, the LTM8083 mod-

ule passes CISPR25 Class 5 conducted and radiated EMI

standards. Refer to Figure 2 and Figure 3 for more details.

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