LTC3604IUD#PBF Datasheet LTC3604IMSE#PBF, LTC3604EMSE#TRPBF, LTC3604EUD#TRPBF | P7-P9

LTC3604

3604fa

For more information www.linear.com/LTC3604

PIN FUNCTIONS

(QFN/MSE)

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

Synchronization Input Pin. This pin places the LTC3604

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 INTV

. 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 LTC3604 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 PV

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 INTV

to PV

+ INTV

INTV

(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.

(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/Exposed Pad Pin 17): Signal Ground Pin.

This pin should have a low noise connection to reference

ground. The feedback resistor network, external compensa-

tion 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.

Connect an external resistor, between 80k to 400k, from

this pin to SGND to program the LTC3604 switching fre-

quency from 800kHz to 4MHz. When RT is tied to INTV

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 INTV

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 LTC3604 will servo the FB pin to the TRACK

voltage under this condition. Above 0.6V, the tracking

function stops and the internal reference resumes control

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

from INTV

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.

(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 (Exposed Pad Pin 17/Pins 3, 4): Power Ground

Pin. The (–) terminal of the input bypass capacitor, C

and the (–) terminal of the output capacitor, C

OUT

, should

be tied to this pin with a low impedance connection. The

exposed package pad must be soldered to the PCB to

provide low impedance electrical contact to ground and

good thermal contact to the PCB.

LTC3604

3604fa

For more information www.linear.com/LTC3604

FUNCTIONAL BLOCK DIAGRAM

–

15k

RUN

SWITCH

LOGIC

AND

ANTI-

SHOOT

THROUGH

0.48V 1.25V

RUN

INTERNAL

SOFT-START

TRACK/SS

3604 BD

SGND

RUN

PGND

PGOOD

INTV

BOOST

SENSE

–

0.648V

–

0.3V

FOLDBACK

DISABLED

AT START-UP

0.552V

6V0.72V

180k

INT

VCC

OUT

INTV

ITH

VCC

BOOST

–

1.4µA

THB

CMP

REV

3.3V

REG

CONTROLLER

OSC

PLL-SYNC

OSC

0.6V

REF

S Q

MODE/SYNC

VON

ION

LTC3604

3604fa

For more information www.linear.com/LTC3604

OPERATION

The LTC3604 is a current mode, monolithic, step-down

regulator capable of providing up to 2.5A of output current.

Its unique controlled on-time architecture allows extremely

low step-down ratios while maintaining a constant switch-

ing frequency. Part operation is enabled by raising the

voltage on the RUN pin above 1.25V nominally.

Main Control Loop

In normal operation the internal top power MOSFET is

turned on for a fixed interval determined by an internal

one-shot timer (“ON” signal in the Block Diagram). When

the top power MOSFET turns off, the bottom power MOS-

FET turns on until the current comparator, I

CMP

, trips,

thus restarting the one-shot timer and initiating the next

cycle. The inductor current is monitored by sensing the

voltage drop across the SW and PGND nodes of the bot-

tom power MOSFET. The voltage at the ITH pin sets the

CMP

comparator threshold corresponding to the induc-

tor valley current. The error amplifier EA adjusts this ITH

voltage by comparing an internal 0.6V reference to the

feedback signal, V

, derived from the output voltage. If, for

example, the load current increases, the feedback voltage

will decrease relative to the internal 0.6V reference. The

ITH voltage then rises until the average inductor current

matches that of the load current.

The operating frequency is determined by the value of the

RT resistor, which programs the current for the internal

oscillator. An internal phase-locked loop servos the switch-

ing regulator on-time to track the internal oscillator edge

and force a constant switching frequency. A clock signal

can be applied to the MODE/SYNC pin to synchronize the

switching frequency to an external source. The regulator

defaults to forced continuous operation once the clock

signal is applied.

At low load currents the inductor current can drop to zero

or become negative. If the LTC3604 is configured for

Burst Mode operation, this inductor current condition is

detected by the current reversal comparator, I

REV

, which

in turn shuts off the bottom power MOSFET and places

the part into a low quiescent current sleep state resulting

in discontinuous operation and increased efficiency at low

load currents. Both power MOSFETs will remain off with

the part in sleep and the output capacitor supplying the

load current until the ITH voltage rises sufficiently to initiate

another cycle. Discontinuous operation is disabled by tying

the MODE/SYNC pin to ground placing the LTC3604 into

forced continuous mode. During forced continuous mode,

continuous synchronous operation occurs regardless of

the output load current.

“Power Good” Status Output

The PGOOD open-drain output will be pulled low if the

regulator output exits a ±8% window around the regulation

point. This condition is released once regulation within a

±5% window is achieved. To prevent unwanted PGOOD

glitches during transients or dynamic V

OUT

changes, the

LTC3604 PGOOD falling edge includes a filter time of

approximately 40µs.

Overvoltage Protection

In order to protect the internal power MOSFET devices

against transient voltage spikes, the LTC3604 constantly

monitors the V

pin for an overvoltage condition. When

rises above 17.5V, the regulator suspends operation

by shutting off both power MOSFETs. Once V

drops

below 16.5V, the regulator immediately resumes normal

operation. The regulator does not execute its soft-start

function when exiting an overvoltage condition.

Short-Circuit Protection

Foldback current limiting is provided in the event the

output is inadvertently shorted to ground. During this

condition the internal current limit (I

LIM

) will be lowered

to approximately one-third its normal value. This feature

reduces the heat dissipation in the LTC3604 during short-

circuit conditions and protects both the IC and the input

supply from any potential damage.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P26

LTC3604IUD#PBF

Mfr. #:

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Manufacturer:

Analog Devices / Linear Technology

Description:

Switching Voltage Regulators 2.5A, 15V Mono Sync Buck Reg

Lifecycle:

New from this manufacturer.

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LTC3604IUD#PBF

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