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LT3506/LT3506A

3506afb

TEMPERATURE (

°C)

–50

0.5

1.0

1.5

2.0

3.0

–25

3506 G12

100 125

2.5

1.4

1.2

1.0

0.8

0.6

0.4

0.2

TEMPERATURE (

°C)

–50

3506 G13

–25

100

125

TO SWITCH

TO RUN

IRUN/SS vs Temperature

RUN/SS Thresholds vs

Temperature

TYPICAL PERFOR A CE CHARACTERISTICS

BOOST1 (Pin 1), BOOST2 (Pin 8): The BOOST pins are

used to provide drive voltages, higher than the input

voltage, to the internal bipolar NPN power switches. Tie

through a diode from VOUT or from VIN.

SW1 (Pin 2), SW2 (Pin 7): The SW pins are the outputs

of the internal power switches. Connect these pins to the

inductors, catch diodes and boost capacitors.

VIN1 (Pins 3, 4): The VIN1 pins supply current to the

LT3506’s internal regulator and to the internal power

switch connected to SW1. These pins must be locally

bypassed.

VIN2 (Pins 5, 6): The VIN2 pins supply current to the inter-

nal power switch connected to SW2 and must be locally

bypassed.ConnectthesepinsdirectlytoVIN1unlesspower

for Channel 2 is coming from a different source.

RUN/SS1 (Pin 13), RUN/SS2 (Pin 12): The RUN/SS pins

are used to shut down the individual switching regula-

tors and the internal bias circuits. They also provide a

soft-start function. To shut down either regulator, pull the

RUN/SS pin to ground with an open drain or collector.

Tie a capacitor from these pins to ground to limit switch

current during start-up. If neither feature is used, leave

these pins unconnected.

PG1 (Pin 14), PG2 (Pin 11): The Power Good pins are

the open collector outputs of an internal comparator. PG

remains low until the FB pin is within 10% of the final

regulation voltage. As well as indicating output regulation,

the PG pins can be used to sequence the two switching

regulators. These pins can be left unconnected. The PG

outputs are valid when VIN is greater than 3.4V and either

of the RUN/SS pins is high. The PG comparators are

disabled in shutdown.

VC1 (Pin 15), VC2 (Pin 10): The VC pins are the outputs of

the internal error amps. The voltages on these pins control

the peak switch currents. These pins are normally used

to compensate the control loops, but can also be used to

override the loops. Pull these pins to ground with an open

drain to shut down each switching regulator.

FB1 (Pin 16), FB2 (Pin 9): The LT3506 regulates each

feedback pin to 800mV. Connect the feedback resistor

divider taps to these pins.

Exposed Pad (Pin 17): The Exposed Pad of the package

providesbothelectricalcontacttogroundandgoodthermal

contact to the printed circuit board. The Exposed Pad must

be soldered to the circuit board for proper operation.

PI FU CTIO S

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