DCR02 SERIES

SBVS028A − DECEMBER 2000 − REVISED APRIL 2004

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5

FUNCTIONAL DESCRIPTION

OVERVIEW

The DCR02 series offers isolation from an unregulated

power supply operating from a choice of input voltages.

This series provides a variety of regulated output voltages

at a nominal output power of 2W.

POWER STAGE

The input supply is chopped at a frequency of 400kHz

(internal oscillator divided by 2), which is used to drive the

center-tapped toroidal transformer.

RECTIFICATION

The transformer output is full wave rectified and smoothed

REGULATOR

The

internal

low-dropout

regulator

provides

a

well-regulated output voltage throughout the operating

range of the device.

OSCILLATOR AND WATCHDOG

The DCR02 uses an internal saw-tooth generator to

provide the 800kHz onboard oscillator that is used to drive

the power switching circuit. The operation of the oscillator

is monitored by the watchdog, which will tri-state the output

driver circuit if the oscillator fails or if the SYNC pin is taken

low (shutdown mode). When the SYNC pin is returned

high, normal operation resumes.

SYNCHRONIZATION

If more than one DCR02 is being used, beat frequencies

and other electrical interference can be generated. This

interference is due to the small variations in switching

frequencies

between

the

converters.

The

DCR02

overcomes this by allowing devices to be synchronized to

one another. Up to eight devices can be synchronized by

connecting the SYNC pins together, with care being taken

to minimize the capacitance of tracking.

Significant stray capacitance on the SYNC pin reduces the

frequency of the internal oscillator. If this reduction is large,

the DCR02 may be taken out with its optimized operating

parameters, and saturation of the magnetics may result,

damaging the device.

If devices are synchronized, it should be noted that all

devices will draw maximum current simultaneously at start

up. This can cause the input voltage to dip. Should it fall

below the minimum input voltage, the devices may not

start up. A low equivalent series resistance (ESR) 2.2

µF

ceramic capacitor should be connected as close to the

device input pins as possible.

If more than eight devices are required to be synchronized,

it is recommended that external synchronization be used.

Details of this procedure are contained in application

report

SBAA035,

External

Synchronization

of

the

DCP01/02 Series of DC/DC Converters, available for

download at www.ti.com.

CONSTRUCTION

The DCR02 is manufactured using the same technology

as standard IC packages. There is no substrate within the

package. The DCR02 is constructed using a driver IC,

low-dropout voltage regulator, rectifier diodes, and a

wound magnetic toroid, all mounted on a leadframe. The

DCR02 requires no special printed circuit board (PCB)

assembly processing, since there is no solder within the

package. The result is an isolated DC/DC converter with

inherently high reliability.