IR3721 datasheet(4/16 Pages) IRF

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IR3721

DATA SHEET

Page 4 of 16

www.irf.com

09/15/08

IC PIN FUNCTIONS

VDD PINS

These pins provide operational bias current to circuits

internal to the IR3721. Bypass them with a high

quality ceramic capacitor to the GND pins.

GND PINS

These pins return operational bias current to system

ground. VO is measured with respect to GND. The

GND pin sinks reference current established by the

external resistor RT.

VO PIN

Since this pin measures DCR voltage drop it is critical

that it be Kelvin connected to the buck inductor

output. Power accuracy may be degraded if the

voltage at this pin is below VOmin.

VCS PIN

A switched current source internal to the IR3721

maintains the average voltage of this pin equal to the

voltage of the VO pin. The average current into this

pin is therefore proportional to buck inductor current.

VRT PIN

A voltage reference internal to the IR3721 drives the

VRT pin while the pin current is monitored and used to

set the amplitude of the current monitor switched

current source IREF. Connect this pin to GND through

a precision resistor network RT. This network may

include provision for canceling the positive

temperature coefficient of the buck inductor’s DC

resistance (DCR).

VK PIN

The voltage of the VK pin is used to modulate the

amplitude of the DI pin. This is one of the terms used

to determine the product of the multiplier output. If VK

is connected to a fixed voltage then the output of the

multiplier is proportional to current. If VK is connected

to the buck converter output voltage then the output

of the DI driven RC filter is proportional to power.

DI PIN

The Dl pin output has a duty ratio proportional to the

current into VCS, and an amplitude equal to the

voltage at the VK pin. The DI pin is intended to drive

an external low pass filter. The output of this filter is

the product of the current and voltage terms.

IR3721 Datasheet(PDF) 4 Page - International Rectifier

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