IR3558 datasheet(13/21 Pages) IRF

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September 10, 2012 | FINAL DATASHEET

IR3558

45A Integrated PowIRstage®

THEORY OF OPERATION

DESCRIPTION

The IR3558 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 IR3558 is designed to work with a PWM controller.

It accepts either regular 3.3V tri-state PWM signal or

International Rectifier’s Active Tri-Level (ATL) PWM signal,

which is selectable by MODE pin.

The IR3558 provides Enable input to control the converter

output and reduce quiesecent current.

The IR3558 provides a over temperature fault signal

capable of detecting an over-temperature condition in the

vicinity of the power stage. The over-temperature

threshold is programmable from 70°C to 150°C.

PWM MODE SELECTION

The IR3558 features a MODE pin which allows operation

with two different PWM signal levels. Grounding the

MODE pin allows the IR3558 to accept a regular tri-state

PWM with signal from 0V to 3.3V for low to high

transitions. A PWM voltage level in the tri-state window of

0.85V and 2.55V for 80ns hold off time results in turning

off both the control and synchronous MOSFETs. Floating

MODE pin or connecting it to VCC enables the IR3558 to

accept IR’s proprietary ATL mode, in which the PWM

voltage level is from 0V to 1.8V for low to high transitions.

A PWM voltage level greater than the tri-state high

threshold (2.5V typical) turns off both the control and

synchronous MOSFETs.

REGULAR 3.3V PWM MODE

If MODE pin is grounded, the IR3558 accepts regular 3-

level 3.3V PWM input signals. As shown in Figure 6, when

PWM input is above VPWM_HIGH, the synchronous MOSFET is

turned off and the control MOSFET is turned on. When

PWM input is below VPWM_LOW, the control MOSFET is

turned off and synchronous MOSFET is turned on. If PWM

pin is floated, the built-in resistors pull the PWM pin into a

tri-state region centered around 1.6V. Figures 19-23 show

the PWM input and the corresponding SW and GATEL

output of the IR3558.

ACTIVE TRI-LEVEL PWM MODE

When MODE pin is floating, the IR3558 accepts a unique

tri-level PWM control signal provided by an IR digital PWM

controller. As shown in Figure 7, the rising and falling

edges of the PWM signal transition between 0V and 1.8V

to switch both the control and synchronous MOSFETs

during normal PWM operation. To turn both MOSFETs off

simultaneously, the PWM signal crosses a tri-state voltage

level higher than the VATL_TRI_HIGH threshold (2.5V typical).

This threshold based tri-state results in a very fast disable

with only a small propagation delay. MOSFET switching

resumes when the PWM signal falls below the VATL_TRI_LOW

threshold (2.3V typical) into the normal PWM operating

voltage range. Figures 24-28 show the PWM input and the

corresponding SW and GATEL output of the IR3558.

This fast tri-state operation eliminates the need for the

PWM signal to dwell in the shutdown window, eliminating

the delay time created by the PWM pull-up and pull-down

resistors with the PWM trace routing capacitance. A

dedicated Body-Braking® pin is not required, which

simplifies the routing and layout.

One advantage of the ATL is the ability to quickly turn-off

all synchronous MOSFETs during a load release event. This

is known as Body-Braking® since all the load current is

forced to flow momentarily through the body diodes of the

MOSFETs, which discharges the inductor current faster and

results in a much lower overshoot on the output voltage.

The IR3558 provides a 1mA typical pull-up current to drive

the PWM input to the tri-state condition of 3.3V when the

PWM controller output is in its high impedance state. The

1mA typical current is designed for driving worst case stray

capacitances and transition the IR3558 into the tri-state

condition rapidly to avoid a prolonged period of

conduction of the control or synchronous MOSFET during

faulty conditions. Once the PWM signal has been pulled

up, the 1mA current is disabled to reduce power

consumption.

ENABLE CONTROL

EN is a 3.3V logic input. Logic low disables PWM operation

and places the power stage in tri-state, as shown in Figure

29. It also places the driver in a low power state with

minimum quiescent current. Logic high enables the device.

INTEGRATED BOOTSTRAP DIODE

The bootstrap circuit is used to establish the gate voltage

for the high-side driver. It consists of a diode and capacitor

IR3558 Datasheet(PDF) 13 Page - International Rectifier

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