LT3504IUFD データシートの表示（PDF） - Linear Technology

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LT3504IUFD

Quad 40V/1A Step-Down Switching Regulator with 100% Duty Cycle Operation

Linear Technology 

LT3504

Pin Functions

DA (Pins 1, 3, 6, 8): Return the Schottky catch diode

anode to the diode anode (DA) pin. An internal compara-

tor senses the diode current and prevents switching when

the diode current is higher than the DA pin current limit.

SW (Pins 2, 4, 5, 7): The SW pins are the output of the

internal power switches. Connect each SW pin to an in-

ductor and Schottky catch diode cathode.

VIN (Pins 9, 11, 26, 28): The VIN pins supply current to

the LT3504’s internal regulator and to the internal power

switches. The VIN pins should be tied together and locally

bypassed with a capacitor to ground, preferably to pins

10 and 27.

GND (Pins 10, 18, 27, Exposed Pad Pin 29): Tie the GND

pins to a local ground plane below the LT3504 and the

circuit components. The exposed pad must be soldered

to the PCB and electrically connected to ground. Use a

large ground plane and thermal vias to optimize thermal

performance.

RUN/SS (Pins 12, 13, 14, 15): The RUN/SS pins are used

to soft start each channel and to allow each channel to

track other outputs. Output tracking is implemented by

connecting a resistor divider to this pin from the tracked

output. For soft start, tie a capacitor from this pin to ground.

An internal 1.3µA soft-start current charges the capacitor

to create a voltage ramp at the pin. Each channel can be

individually shut down by pulling RUN/SS below 0.1V.

EN/UVLO (Pin 16): The EN/UVLO pin is used to start up

the internal regulator to power the reference and oscilla-

tor. It also starts up the internal boost regulator. Pull the

EN/UVLO pin below 1.44V to shut down the LT3504. The

LT3504 will draw less than 10µA of current from the VIN

pin when EN/UVLO is less than 1.44V. Pull EN/UVLO pin

below 0.7V to put the LT3504 in a state where the part

draws 0µA from the VIN pin. The threshold can function

as an accurate undervoltage lockout (UVLO), preventing

the regulator from operating until the input voltage has

reached the programmed level. Do not drive the EN/UVLO

pin more than 5V above VIN.

RT/SYNC (Pin 17): Set the switching frequency of the

LT3504 by tying an external resistor from this pin to

ground. Select the value of the programming resistor

(RT) according to Table 1 in the Applications Information

section. The RT/SYNC pin is also used to synchronize the

internal oscillator of the LT3504 to an external signal. The

synchronization (sync) signal is directly logical compatible

and can be driven by any signal with pulse width greater

than 50ns. The synchronization range is from 250kHz to

2.2MHz.

FB (Pins 19, 20, 21, 22): Each feedback pin is regulated

to 800mV. Connect the feedback resistor divider to this

pin. The output voltage is programmed according to the

following equation:

R1 =

R2

•

⎛

⎝⎜

VOUT

0.8V

−

1⎞⎠⎟

where R1 connects between OUT and FB, and R2 connects

between FB and GND. A good value for R2 is 10kΩ.

PG (Pin 23): The Power Good pin is the open collector

output of an internal comparator. PG remains low until

all FB pins are greater than 710mV. If not in use, this pin

can be left unconnected. The PG comparator is disabled

in shutdown.

SW5 (Pin 24): The SW5 pin is an open collector of an

internal boost regulator power switch. This power switch

generates the drive voltage 4.85V above the input voltage

(VIN), to drive the internal buck regulator power switches.

Connect an inductor from this pin to the VIN pin.

SKY (Pin 25): The SKY pin is the output of an integrated

power Schottky diode and is the source of drive voltage

to the internal buck regulator power switches. Connect a

1µF capacitor from this pin to the VIN pin. Do not drive this

pin with an external voltage source. Do not draw current

from this pin with an external component.

For more information www.linear.com/LT3504

3504fa

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