LTC3313JVPBF datasheet(9/28 Pages) AD

9 / 28 page

LTC3313

Rev. 0

For more information www.analog.com

PIN FUNCTIONS

EN (Pin 1): The EN pin has a precision enable threshold

with hysteresis. An optional external resistor divider, from

VIN or from another supply, programs the threshold below

which the LTC3313 will shut down. If the precision thresh-

old is not used, directly connect the pin to VIN. When the

EN pin is low, the LTC3313 enters a low current shutdown

mode where all internal circuitry is disabled.

AGND (Pin 2): The AGND pin is the output voltage remote

ground sense. Connect the AGND pin directly to the nega-

tive terminal of the output capacitor at the load and to the

feedback divider resistor.

VIN (Pins 3, 4, 11, 12): The VIN pins supply current to the

internal circuitry and topside power switch. All of the VIN

pins must be connected together with short, wide traces

and bypassed to PGND with low ESR capacitors located

as close as possible to the pins.

PGND (Pins 5, 10, 19): The PGND pins are the return

path of the internal bottom side power switch. Connect

the PGND pins together and to the exposed pad. Connect

the negative terminal of the input capacitors as close to

the PGND pins as possible. The PGND node is the main

thermal highway and should be connected to a large PCB

ground plane with many large vias.

SW (Pins 6–9): The SW pins are the switching outputs of

the internal power switches. Connect these pins together

to the inductor with short, wide traces.

MODE/SYNC (Pin 13): The MODE/SYNC pin facilitates

multiphase operation and synchronization to an external

clock. Depending on the mode of operation, the MODE/

SYNC pin either accepts an input clock pulse or outputs

a clock pulse at its operating frequency. (see Multiphase

Operation in Applications Information). The MODE/SYNC

pin also programs the mode of operation: pulse-skipping

or forced continuous.

PGOOD (Pin 14): The PGOOD pin is a power good pin and

is the open drain output of an internal comparator. The

PGOOD output is pulled low when VIN is above 2.25V and

the part is in shutdown. When connecting multiple phases

in parallel, connect the PGOOD pins together.

RT (Pin 15): The RT pin sets the oscillator frequency

with an external resistor to AGND or sets the phasing

for multiphase operation (see Multiphase Operation in

Applications Information).

SSTT (Pin 16): Soft-Start, Track, Temperature Monitor.

An internal 10µA current into an external capacitor at the

soft-start pin programs the output voltage ramp rate dur-

ing start-up. During the soft-start cycle, the FB pin voltage

will track the SSTT pin voltage. When the soft-start cycle

is complete, the tracking function is disabled, the internal

reference resumes control of the error amplifier and the

SSTT pin servos to a voltage representative of junction

temperature. For a clean recovery from an output short

circuit condition, the SSTT pin is pulled down to approxi-

mately 140mV above the VFB voltage and a new soft-start

cycle is initiated. During shutdown and fault conditions,

the SSTT pin is pulled to ground.

ITH (Pin 17): The ITH pin is the compensation node for

the output voltage regulation control loop. Compensation

components connected to this pin are referenced to AGND.

FB (Pin 18): The feedback pin is externally connected to

the output voltage via a resistive divider and is internally

connected to the inverting input of the error amplifier.

The LTC3313 regulates the FB pin to 500mV. A phase-

lead capacitor connected between FB and VOUT is used to

optimize the transient response.

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