IR3086A

IR3086A THEORY OF OPERATION

Block Diagram

The Block diagram of the IR3086A is shown in Fig. 6, and specific features are discussed in the following sections.

VCC

VDAC

BIASIN

SCOMP

VDAC

20mV

RAMP

SLOPE

ADJUST

VOLTAGE

PROPORTIONAL

TO ABSOLUTE

TEMPERATURE

ENABLE

FAULT

COMPARATOR

+

-

+

-

+

-

+

-

+

-

10K

+

-

RMPIN+

VCC

EAIN

RMPIN-

SCOMP

PWMRMP

ISHARE

GATEH

LGND

BIASIN

PGND

VCCH

VCCL

CSIN+

GATEL

PHSFLT

VRHOT

HOTSET

CSIN-

DACIN

INTERNAL

CIRCUIT

BIAS

SHARE

ADJUST

ERROR

AMP

CLOCK

PULSE

GENERATOR

RAMP

COMPARATOR

SYSTEM

REFERENCE

VOLTAGE

BODY BRAKING

COMPARATOR

R

S

DOMINANT

PWM

COMPARATOR

RESET

PWM

LATCH

ENABLE

OVP

COMPARATOR

2V

X34

CURRENT

SENSE

AMP

GATE

NON-OVERLAP

COMPARATORS

X

0.91

125mV

RAMP

DISCHARGE

CLAMP

VDAC

+

+

VRHOT

COMPARATOR

Figure 6 – IR3086A Block Diagram

Tri-State Gate Drivers

The gate drivers can deliver up to 3A peak current. An adaptive non-overlap circuit monitors the voltage on the

GATEH and GATEL pins to prevent MOSFET shoot-through current while minimizing body diode conduction.

An Enable signal is provided by the Control IC to the Phase IC without the addition of a dedicated signal line. The

Error Amplifier output of the Control IC drives low in response to any fault condition such as input under voltage or

output overload. The IR3086A Body Braking

state operation prevents negative inductor current and negative output voltage during power-down.

The Gate Drivers revert to a high impedance “off” state if VCCL and VCCH supply voltages are below the normal

operating range. An 80kΩ resistor is connected across the GATEH/GATEL and PGND pins to prevent the

GATEH/GATEL voltage from rising due to leakage or other causes under these conditions.

Over Voltage Protection (OVP)

The IR3086A includes over-voltage protection that turns on the low side MOSFET to protect the load in the event of

a shorted high-side MOSFET or connection of the converter output to an excessive output voltage. A comparator

monitors the voltage at the CSIN- pin which is usually connected directly to the converter output. If the voltage

exceeds the DACIN voltage plus 125mV typical (100mV minimum and 160mV maximum) the GATEL pin drives

high. The OVP circuit overrides the normal PWM operation and will fully turn-on the low side MOSFET within

approximately 150ns. The low side MOSFET will remain ON until the over-voltage condition ceases.

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