IR3598 datasheet(16/21 Pages) IRF

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Dual/Doubler Interleaved MOSFET Driver

October 25, 2013 | FINAL | V1.12

IR3598

This fast tri‐state operation eliminates the need for any

tri‐state hold‐off time of the PWM signal to dwell in the

shutdown window. Dedicated disable or enable pins are

not required which simplifies the routing and layout in

applications with a limited number of board layers. It also

provides switching free of shoot through for slow PWM

transition times of up to 20ns. The IR3598 is therefore

tolerant of stray capacitance on the PWM signal lines.

The IR3598 provides a 1.0mA 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 1.0mA typical current is designed for driving

worst case stray capacitances and transition the IR3598

into the tri‐state condition rapidly to avoid a prolonged

period of conduction of the high or low side MOSFETs

during faults. Immediately after the driver is driven into

the tri‐state mode, the 1mA current is disables such that

power is conserved.

START UP

During initial startup, the IR3598 holds both high‐ and

low‐side drivers low even after POR threshold is reached

if the device is in IR ATL mode. This mode is maintained

while the PWM signal is pulled to the tri‐state threshold

level greater than the tri‐state HI_GATE threshold and until

it transitions out of tri‐state. It is this initial transition out

of the tri‐state which enables both drivers to switch based

on the normal PWM voltage levels.

This startup also ensures that any undetermined PWM

signal levels from a controller in pre‐POR state will not

result in high or low‐side MOSFET turn on until the

controller is out of its POR.

For Tri‐state mode, the POR operation is the same except

the driver does not look for an input tri‐state before

functioning.

HIGH SIDE DRIVER

The high‐side driver drives an external floating N‐channel

MOSFET. An external bootstrap circuit referenced to the

SWITCH node, consisting of a boot diode and capacitor is

used to bias the external MOSFET gate. When the SWITCH

node is at ground, the boot capacitor is charged to near

the supply voltage using the boot diode and this stored

charge is used to turn on the external MOSFET when the

PWM signal goes high. Once the high‐side MOSFET is

turned on, the SWITCH voltage rises to the supply voltage

and the boot voltage rises to equal to the supply voltage

plus the VDRV voltage less the diode forward voltage.

When the PWM signal goes low, the MOSFET is turned off

by pulling the MOSFET gate to the SWITCH voltage.

LOW SIDE DRIVER

The IR3598 low‐side driver is designed to drive an external

N‐channel MOSFET referenced to ground. The low‐side

driver is connected internally to the supply voltage to turn

the MOSFET on.

When the low‐side MOSFET is turned on the SWITCH node

is pulled to ground. This allows charging of the boot

capacitor to the supply voltage ready to drive the high‐side

MOSFET based on the PWM signal level.

ADAPTIVE DEAD TIME ADJUSTMENT

In a synchronous buck configuration dead time between

the turn off of one MOSFET and turn on of the other is

necessary to prevent simultaneous conduction.

This prevents a shoot‐through condition which would

result in a short of the supply voltage to ground. A fixed

dead time does not provide optimal performance over a

variety of MOSFETs, converter duty cycles and board

layouts.

The IR3598 provides an ‘adaptive’ dead time adjustment.

This feature minimizes dead time to an optimum duration

which allows for maximum efficiency. The ‘break before

make’ adaptive design is achieved by monitoring gate and

SWITCH voltages to determine OFF status of a MOSFET.

It also provides zero‐voltage switching (ZVS) of the low side

MOSFET with minimum current conduction through its

body‐diode.

When operating in IR ATL mode, and the PWM is switching

between 1.8V and 0V, its falling edge transition from high

to low will turn off the high side gate driver. The adaptive

dead time circuit monitors the HI_GATE and the SWITCH

node voltages during the high side MOSFET turn off. When

the HI_GATE falls below 1.25V above the SWITCH node

potential or the SWITCH node voltage drops below 1.38 V

the high side MOSFET is determined to be turned off and

the LO_GATE turn on is initiated. This turns on the external

low‐side MOSFET. The rising edge transition of the PWM

signal from low to high voltage causes the low‐side gate

driver to turn off. The adaptive circuit monitors the voltage

at LO_GATE and when it falls below 1.38V, the low‐side

MOSFET is determined to be turned off and the high‐side

MOSFET turn on is initiated.

IR3598 Datasheet(PDF) 16 Page - International Rectifier

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