LTM8003 datasheet(11/26 Pages) LINER

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LTM8073

8073fa

For more information www.linear.com/LTM8073

pin FuncTions

AUX (Pin B2): Low Current Voltage Source for BIAS.

In many designs, the BIAS pin is simply connected to

VOUT. The AUX pin is internally connected to VOUT and

is placed adjacent to the BIAS pin to ease printed cir-

cuit board routing. Also, some applications require a

feed-forward capacitor; it can be connected from AUX

to FB for convenient PCB routing. Although this pin is

internally connected to VOUT, it is not intended to deliver

a high current, so do not draw current from this pin to

the load.

SYNC (Pin B4): External clock synchronization input

and operational mode. This pin programs four different

operating modes: 1) Burst Mode®. Tie this pin to ground

for Burst Mode operation at low output loads—this

will result in low quiescent current. 2) Pulse-skipping

mode. Float this pin for pulse-skipping mode. This mode

offers full frequency operation down to low output loads

before pulse-skipping mode occurs. 3) Spread spectrum

mode. Tie this pin high (between 2.9V and 4.2V) for

pulse-skipping mode with spread spectrum modulation.

4) Synchronization mode. Drive this pin with a clock

source to synchronize to an external frequency. During

synchronization the part will operate in pulse-skipping

mode.

TR/SS (Pin B5): The TR/SS pin is used to provide a

soft-start or tracking function. The internal 2μA pull-up

current in combination with an external capacitor tied

to this pin creates a voltage ramp. If TR/SS is less than

0.8V, the FB voltage tracks to this value. For tracking, tie

a resistor divider to this pin from the tracked output. This

pin is pulled to ground with an internal MOSFET during

shutdown and fault conditions; use a series resistor if

driving from a low impedance output. This pin may be

left floating if the tracking function is not needed.

RUN (Pin B6): Pull the RUN pin below 0.9V to shut down

the LTM8073. Tie to 1.06V or more for normal opera-

tion. If the shutdown feature is not used, tie this pin to

the VIN pin.

block DiagraM

AUX

BIAS

VOUT

VIN

GND

RUN

TR/SS

SYNC

8073 BD

CURRENT

MODE

CONTROLLER

0.2µF

10pF

0.1µF

249k

2.2µH

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