LTC3601IMSE datasheet(7/24 Pages) LINER

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LTC3601

3601f

PIN FUNCTIONS (QFN/MSE)

MODE/SYNC (Pin 1/Pin 15): Mode Selection and External

Synchronization Input Pin. This pin places the LTC3601

into forced continuous operation when tied to ground.

High efﬁciency Burst Mode operation is enabled by either

ﬂoating this pin or by tying this pin to INTVCC. When driven

with an external clock, an internal phase-locked loop will

synchronize the phase and frequency of the internal oscil-

lator to that of the incoming clock signal. During external

clock synchronization, the LTC3601 will default to forced

continuous operation.

PGOOD (Pin 2/Pin 16): Open-Drain Power Good Output

Pin. PGOOD is pulled to ground when the voltage at the

FB pin is not within 8% (typical) of the internal 0.6V

reference. PGOOD becomes high impedance once the

voltage at the FB pin returns to within ±5% (typical) of

the internal reference.

SW (Pins 3, 4/Pins 1, 2): Switch Node Output Pin. Con-

nect this pin to the SW side of the external inductor. The

normal operation voltage swing of this pin ranges from

ground to PVIN.

BOOST (Pin 6/Pin 5): Boosted Floating Driver Supply

Pin. The (+) terminal of the external bootstrap capacitor

connects to this pin while the (–) terminal connects to

the SW pin. The normal operation voltage swing of this

pin ranges from a diode voltage drop below INTVCC up

to PVIN + INTVCC.

INTVCC (Pin 7/Pin 6): Internal 3.3V Regulator Output Pin.

This pin should be decoupled to PGND with a low ESR

ceramic capacitor of 1μF or more.

VON (Pin 8/Pin 7): On-Time Voltage Input Pin. This pin

sets the voltage trip point for the on-time comparator. Con-

nect this pin to the regulated output to make the on-time

proportional to the output voltage. The pin impedance is

normally 180kΩ.

SGND (Pin 9/Pin 17): Signal Ground Pin. This pin should

have a low noise connection to reference ground. The

feedback resistor network, external compensation network

and RT resistor should be connected to this ground. In

the MSE package, this pin must be soldered to the PCB

to provide a good thermal contact to the PCB.

RT (Pin 10/Pin 8): Oscillator Frequency Program Pin. Con-

nect an external resistor, between 80k to 400k, from this

pin to SGND to program the LTC3601 switching frequency

from 800kHz to 4MHz. When RT is tied to INTVCC, the

switching frequency will default to 2MHz.

FB (Pin 11/Pin 9): Output Voltage Feedback Pin. Input to

the error ampliﬁer that compares the feedback voltage to

the internal 0.6V reference voltage. Connect this pin to

the appropriate resistor divider network to program the

desired output voltage.

ITH (Pin 12/Pin 10): Error Ampliﬁer Output and Switching

Regulator Compensation Pin. Connect this pin to appro-

priate external components to compensate the regulator

loop frequency response. Connect this pin to INTVCC to

use the default internal compensation.

TRACK/SS (Pin 13/Pin 11): Output Voltage Tracking and

Soft-Start Input Pin. Forcing a voltage below 0.6V on

this pin overrides the internal reference input to the error

ampliﬁer. The LTC3601 will servo the FB pin to the TRACK

voltage under this condition. Above 0.6V, the tracking func-

tion stops and the internal reference resumes control of

the error ampliﬁer. An internal 1.4μA pull-up current from

INTVCC allows a soft-start function to be implemented by

connecting an external capacitor between this pin and

ground. See Applications Information section for more

details.

RUN (Pin 14/Pin 12): Regulator Enable Pin. Enables chip

operation by applying a voltage above 1.25V. A voltage

below 1V on this pin places the part into shutdown. Do

not ﬂoat this pin.

VIN (Pins 15, 16/Pins 13, 14): Main Power Supply Input

Pins. These pins should be closely decoupled to PGND

with a low ESR capacitor of 10μF or more.

PGND (Pin 17/Pins 3, 4): Power Ground Pin. The (–)

terminal of the input bypass capacitor, CIN, and the (–)

terminal of the output capacitor, COUT, should be tied to

this pin with a low impedance connection. In the QFN

package this pin must be soldered to the PCB to provide

low impedance electrical contact to ground and good

thermal contact to the PCB.

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