IR3553_15 datasheet(13/22 Pages) IRF

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July 16, 2014 | DATASHEET V3.3

IR3553

40A Integrated PowIRstage®

THEORY OF OPERATION

DESCRIPTION

The IR3553 PowIRstage® is a synchronous buck driver with

co-packed MOSFETs with integrated Schottky diode, which

provides system designers with ease of use and flexibility

required in cutting edge CPU, GPU and DDR memory

power delivery designs and other high-current low-profile

applications.

The IR3553 is designed to work with a PWM controller.

It incorporates a continuously self-calibrated current sense

amplifier, optimized for use with inductor DCR sensing.

The current sense amplifier provides signal gain and noise

immunity, supplying multiphase systems with a superior

design toolbox for programmed impedance designs.

The IR3553 provides a phase fault signal capable

of detecting open or shorted MOSFETs, or an over-

temperature condition in the vicinity of the power stage.

The IR3553 accepts an active low Body-Braking® input

which disables both MOSFETs to enhance transient

performance or provide a high impedance output.

The IR3553 provides diode emulation feature which avoids

negative current in the synchronous MOSFET and improves

light load efficiency.

The IR3553 PWM input is compatible with 3.3V logic signal

and 7V tolerant. It accepts 3-level PWM input signals with

tri-state.

BBRK# PIN FUNCTIONS

The BBRK# pin has two functions. During normal

operation, it accepts direct control signal from the PWM

controller to enable Body-Braking®, which turns off both

control and synchronous MOSFETs to improve the load

transient response.

The second function of BBRK# pin is to select Body-

Braking® (tristate) or diode emulation mode when PWM

pin receives a tri-state signal. The seletion is recongnized

right after VCC passes its UVLO threshold during the VCC

power up. If the BBRK# input is always high, the default

operation mode is Body- Braking®, in which both MOSFETs

will be turned off when the PWM input is in tri-state. If the

BBRK# input has been pulled low for at least 20ns after the

VCC passes its UVLO threshold during power up, the diode

emulation mode is set. PWM input in tri-state will activate

a synchronous diode emulation feature allowing designers

to maximize system efficiency at light loads without

compromising transient performance. Once the diode

emulation mode is set, it cannot be reset until the VCC

power is recycled.

PWM TRI-STATE INPUT

The IR3553 PWM accepts 3-level input signals. When PWM

input is high, the synchronous MOSFET is turned off and

the control MOSFET is turned on. When PWM input is low,

control MOSFET is turned off and synchronous MOSFET is

turned on. Figures 16-18 show the PWM input and the

corresponding SW and GATEL output. If PWM pin is floated

, the built-in resistors pull the PWM pin into a tri-state

region centered around 1.65V.

When PWM input voltage is in tri-state region, the IR3553

will go into either Body-Braking® mode or diode emulation

mode depending on BBRK# selection during VCC power up.

BODY-BRAKING® MODE

International Rectifier’s Body-Braking® is an operation

mode in which two MOSFETs are turned off. When the

synchronous MOSFET is off, the higher voltage across the

Shottky diode in parallel helps discharging the inductor

current faster, which reduces the output voltage

overshoot. The Body-Braking® can be used either to

enhance transient response of the converter after load

release or to provide a high impedance output.

There are two ways to place the IR3553 in Body-Braking®

mode, either controlling the BBRK# pin directly or through

a PWM tri-state signal. Both control signals are usually

from the PWM controller.

Pulling BBRK# low forces the IR3553 into Body-Braking®

mode rapidly, which is usually used to enhance converter

transient response after load release, as shown in Figure

19. Releasing BBRK# forces the IR3553 out of Body-

Braking® mode quickly.

The BBRK# low turns off both MOSFETs and therefore can

also be used to disable a converter. Please note that soft

start may not be available when BBRK# is pulled high to

enable the converter.

If the BBRK# input is always high, the Body-Braking® is

activated when the PWM input enters the tri-state region,

as shown in Figures 20 and 21. Comparing to pulling down

the BBRK# pin directly, the Body-Braking® response to

PWM tri-state signal is slower due to the hold-off time

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