IRS27951S

IRS27952(4)S

11

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© 2012 International Rectifier

November 8

VCC: Power Supply Voltage

This is the supply voltage pin of the IC and sense node for the under-voltage lock out circuit. It is possible to turn off

not internally clamped.

RT: Oscillator timing resistor

This pin provides a precise 2V reference and a resistor connected from this pin to COM defines a current that is

used to set the minimum oscillator frequency. To close the feedback loop that regulates the converter output

voltage by modulating the oscillator frequency, the phototransistor of an optocoupler will be connected to this pin

through a resistor. The value of this resistor will set the maximum operating frequency. An R-C series connected

from this pin to COM sets frequency shift at start-up to prevent excessive energy inrush (soft-start).

CT/SD: Oscillator timing capacitor /Shutdown

An external capacitor CT from this pin to COM sets the dead time and frequency of the oscillator. The CT pin has

sawtooth waveform, which is charged up by the current reference programmed at RT pin during rising slope and is

discharged by an internal fixed 2mA current source during the falling slope. The falling time of the sawtooth defines

the dead-time.

At start-up, a 10uA current source charges this capacitor and the oscillator is enabled only when the voltage at this

pin exceeds VEN1. The IC can also be used to enter sleep mode by externally pulling this pin below VEN2.

COM: Logic and Gate drive Ground

This is ground potential pin of the integrated control circuit. All internal circuits are referenced to this point.

LO: Low-side Gate Drive Output

The driver is capable of 0.3A source and 0.9A sink peak current to drive the lower MOSFET of the half-bridge leg.

The pin is actively pulled to GND during UVLO.

VS: High Side Gate Return/Current Sense

This is the floating supply return. This pin also acts as a high voltage current sense pin and uses the low-side

HO: High-side Gate Drive

The driver is capable of 0.3A source and 0.9A sink peak current to drive the high-side MOSFET in the half-bridge. A

resistor internally connected to pin VS ensures that the pin is not floating during UVLO.

VB: High Side floating supply voltage

The bootstrap capacitor connected between this pin and VS is charged by the bootstrap diode when the low-side

gate-drive is high.