IR11682S datasheet(13/22 Pages) IRF

13 / 22 page

IR11682S

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General Description

The IR11682 Dual Smart Rectifier controller IC is the industry first dedicated high-voltage controller IC for

synchronous rectification in resonant converter applications. The IC can emulate the operation of the two

secondary rectifier diodes by correctly driving the synchronous rectifier (SR) MOSFETs in the two secondary

legs.

The core of this device are two high-voltage, high speed comparators which sense the drain to source voltage

of the MOSFETs differentially. The device current is sensed using the RDSON as a shunt resistance and the

GATE pin of the MOSFET is driven accordingly. Dedicated internal logic then manages to turn the power

device on and off in close proximity of the zero current transition.

IR11682 further simplifies synchronous rectifier control by offering the following power management features:

-Wide VCC operating range allows the IC to be directly powered from the converter output

-Shoot through protection logic that prevents both the GATE outputs from the IC to be high at the same time

-Device turn ON and OFF in close proximity of the zero current transition with low turn-on and turn-off

propagation delays; eliminates reactive power flow between the output capacitors and power transformer

-Internally clamped gate driver outputs that significantly reduce gate losses.

The SmartRectifier™ control technique is based on sensing the voltage across the MOSFET and comparing

it with two negative thresholds to determine the turn on and off transitions for the device. The rectifier current

is sensed by the input comparators using the power MOSFET RDSON as a shunt resistance and its GATE is

driven depending on the level of the sensed voltage vs. the 3 thresholds shown below.

VGate

VTH1

VTH2

VTH3

VDS

Figure 1: Input comparator thresholds

Turn-on phase

When the conduction phase of the SR FET is initiated, current will start flowing through its body diode,

generating a negative VDS voltage across it. The body diode has generally a much higher voltage drop than

the one caused by the MOSFET on resistance and therefore will trigger the turn-on threshold VTH2.

When VTH2 is triggered, IR11682 will drive the gate of MOSFET on which will in turn cause the conduction

voltage VDS to drop down to ID*RDSON. This drop is usually accompanied by some amount of ringing, that

could trigger the input comparator to turn off; hence, a fixed Minimum On Time (MOT) blanking period is

used that will maintain the power MOSFET on for a minimum amount of time.

The fixed MOT limits the minimum conduction time of the secondary rectifiers and hence, the maximum

switching frequency of the converter.

IR11682S Datasheet(PDF) 13 Page - International Rectifier