IR3553 datasheet(13/22 Pages) IRF

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November 29, 2012 | FINAL DATASHEET

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.

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 of the

IR3553. 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 is in tri‐state, two operation modes can

be selected by controlling BBRK# input. 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.

BODY‐BRAKING® MODE

International Rectifier’s Body‐Braking® is a 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/enable a 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

created by the PWM pin parasitic capacitor with the pull‐

up and pull‐down resistors of PWM pin. For better

performance, no more than 100pF parasitic capacitive load

should be present on the PWM line of IR3553.

SYNCHRONOUS DIODE EMULATION MODE

An additional feature of the IR3553 is the synchronous

diode emulation mode. This function enables increased

efficiency by preventing negative inductor current from

flowing in the synchronous MOSFET.

As shown in Figure 22, when the PWM input enters the tri‐

state region the control MOSFET is turned off first, and the

synchronous MOSFET is initially turned on and then is

turned off when the output current reaches zero. If the

sensed output current does not reach zero within a set

amount of time the gate driver will assume that the output

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