IR3551MTRPBF International Rectifier, IR3551MTRPBF Datasheet - Page 13

• Manufacturer Part Number: IR3551MTRPBF
• Description: The IR3551 integrated PowIRstage is a synchronous buck gate driver IC with co-packed control and synchronous MOSFETs and Schottky diode.
• Manufacturer: International Rectifier

Specifications of IR3551MTRPBF

• Package: PQFN / 5 x 6
• Iout (a): 50
• Switch Freq (khz): up to 1.0MHz
• Input Range (v): 4.5 - 15
• Output Range (v): 0.25 - (VCC -2.5)

THEORY OF OPERATION
DESCRIPTION
The IR3551 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 IR3551 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 IR3551 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 IR3551 accepts an active low Body-Braking® input
which disables both MOSFETs to enhance transient
performance or provide a high impedance output.
The IR3551 provides diode emulation feature which avoids
negative current in the synchronous MOSFET and improves
light load efficiency.
The IR3551 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 IR3551 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
IR3551. 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
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March 12, 2012 | FINAL DATASHEET
50A Integrated PowIRstage®
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 IR3551 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 IR3551 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 IR3551 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 IR3551.
SYNCHRONOUS DIODE EMULATION MODE
An additional feature of the IR3551 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
IR3551