DCR01 Series

SBVS013C

FUNCTIONAL DESCRIPTION

OVERVIEW

The DCR01 series offers isolation from an unregulated

power supply operating from a choice of input voltages. The

DCR01s provide a variety of regulated output voltages at a

nominal output power of 1W or above.

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’s output is full wave rectified and smoothed

by the external capacitor connected to V

REC

REGULATOR

The internal low drop-out regulator provides a well-regu-

lated output voltage, throughout the operating range of the

device.

OSCILLATOR AND WATCHDOG

The DCR01 uses an internal saw-tooth generator to provide

the 800kHz on-board 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 DCR01 is being used, beat frequencies and

other electrical interference can be generated. This is due to

the small variations in switching frequencies between the

converters.

The DCR01 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 will have the

effect of reducing the frequency of the internal oscillator. If

this is large, the DCR01 may be taken outside 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 2.2µF

capacitor (low ESR) should be connected as close to the

device input pins as possible for the 5V input devices, and a

0.47µF capacitor for the 12V and 24V devices.

If more than eight devices are required to be synchronized, it

is recommended that external synchronization be used. Details

are contained in Texas Instruments Application Report

literature number SBAA035 (AB-153) available at www.ti.com.

CONSTRUCTION

The DCR01 is manufactured using the same technology as

standard IC packages. There is no substrate within the

package. The DCR01 is constructed using a driver IC, low-

dropout voltage regulator, rectifier diodes, and a wound

magnetic toroid, all mounted on a leadframe. The DCR01

requires no special PCB assembly processing, as there is no

solder within the package. The result is an isolated DC/DC

converter with inherently high reliability.

ADDITIONAL FUNCTIONS

DISABLE/ENABLE

The DCR01 can be disabled or enabled by driving the SYNC

pin using an open drain CMOS gate. If the SYNC pin is

pulled LOW, the DCR01 will be disabled. The disable time

depends upon the external loading. The internal disable

function is implemented in 2µs. Removal of the pull down

will enable the DCR01.

Capacitance loading on the SYNC pin should be minimized

in order to prevent a reduction in the internal oscillator‘s

frequency. See Application Report (

SBAA035)

“External

Synchronization of the DCP01/02 Series of DC/DC Con-

verters”. This document contains information on how to null

the effects of additional capacitance on the SYNC pin. The

oscillator’s frequency can be measured at V

REC

, as this is the

fundamental frequency of the ripple component.

OUTPUT ENABLE/DISABLE

The regulated output of the DCR01 can be disabled by pulling

the ENABLE pin LOW (connect ENABLE to 0V

OUT

). Hold-

ing the ENABLE pin HIGH (connect ENABLE to V

REC

)

enables the regulated output voltage, thus allowing the output

to be controlled from the isolated side, see Figure 1.

DCR 01

OUT

NOTE: (1) 2.2µF capacitor with low ESR for 5V

devices and 0.47µF for 12V and 24V devices.

OUT

= 0.1µF

ERR

= 10kΩ

FILTER

= 1µF

OUT

ENABLE

REC

ERROR

SYNC

ERROR

SW1

see text

FIGURE 1. DCR01 with a Single Output.

DCR01 Series

SBVS013C

ERROR FLAG

The DCR01 has an ERROR pin which provides a “power

good” flag, as long as the internal regulator is in regulation.

DECOUPLING

Ripple Reduction

Due to the very low forward resistance of the DMOS

switching transistors, high current demands are placed upon

the input supply for a short time. By using a good quality

low Equivalent Series Resistance (ESR) capacitor of 2.2µF

(minimum) for the 5V input devices and a 0.47µF capacitor

for the 12V and 24V devices, placed close to the IC supply

input pins, the effects on the power supply can be mini-

mized.

The high switching frequency of 400kHz allows relatively

small values of capacitors to be used for filtering the recti-

fied output voltage. A good quality low ESR capacitor of

1µF placed close to the V

REC

pin and output ground will

reduce the ripple.

It is not recommended that the DCR01 be fitted using an

IC socket as this will degrade performance.

The output at V

REC

is full wave rectified and produces a

ripple of 800kHz.

It is recommended that a 0.1µF low ESR capacitor is

connected close to the output pin and ground to reduce noise

on the output. The capacitor values listed are minimum

values. If lower ripple is required then the filter capacitor

should be increased in value to 2.2µF.

NOTE: As with all switching power supplies the best

performance is only obtained with low ESR capacitors

connected close to the switcher. If low ESR capacitors are

not used, the ESR will generate a voltage drop when the

capacitor is supplying the load power. Often a larger capaci-

tor is chosen for this purpose when a low ESR smaller

capacitance would perform as well.

APPLICATION NOTES

DCR01 SINGLE VOLTAGE OUTPUT

The DCR01 can be used to provide a single voltage output

by connecting, see Figure 1. The ERROR output signal will

be pulled up to the value of V

OUT

for the particular DCR01

being used. The value of R

ERR

will depend on the loading on

the ERROR line however, the total load on the ERROR line

must not exceed the value given in the specification.

The output may be permanently enabled by connecting the

ENABLE pin to the V

REC

pin. The DCR01 may be enabled

remotely by connecting the ENABLE pin to V

REC

via a pull-

up resistor (R

), the value of this resistor is not critical for

the DCR01 as only a small current flows. The switch SW1 can

be used to pull the ENABLE pin LOW, thus disabling the

output. The switching devices can be a bipolar transistor, FET

or a mechanical device, the main load that it will see is R

GENERATING TWO POSITIVE

OUTPUT VOLTAGES

Two DCR01s can be used to create output voltages of +3.3V

and +5V, as shown in Figure 2. The two DCR01s are

connected in self-synchronization, thus locking the oscilla-

tors of both devices to a single frequency.

The ERROR and ENABLE facilities may be used in a

similar configuration for a single DCR01. The filter capaci-

tors connected to the V

REC

pins (C

FILTER

), should be kept

separate from each other and connected in close proximity to

their respective DCR01. If similar output voltages are being

used, it is not recommended that a single filter capacitor

(with an increased capacitance) be used with both V

REC

pins

connected together, as this could result is the overloading of

one of the devices.

DCR 01

OUT

(1)

OUT

= 0.1µF

ERR

= 10kΩ

FILTER

= 1µF

ENABLE

REC

ERROR

SYNC

ERROR

DCR 01

OUT

(1)

OUT

= 0.1µF

ERR

= 10kΩ

FILTER

= 1µF

ENABLE

REC

ERROR

SYNC

OUT

ERROR

NOTE: (1) 2.2µF capacitor with low ESR for 5V

devices and 0.47µF for 12V and 24V devices.

FIGURE 2. Generating Two Positive Voltages from Self-Synchronized DCR01s.

DCR01 Series

SBVS013C

GENERATION OF DUAL POLARITY VOLTAGES

FROM TWO SELF-SYNCHRONIZED DCR01s

Two DCR01s can be configured to produce a dual polarity

supply (i.e., ±5V); the circuit must be connected as shown in

Figure 3.

It must be observed that both devices are producing a

positive regulated output, therefore the ERROR, ENABLE,

and V

REC

are all relative to that particular devices 0V and

must not be directly connected together, or in the case of the

negative output device connected to the common 0V output.

PCB LAYOUT

RIPPLE AND NOISE

Careful consideration should be given to the layout of the

PCB in order for the best results to be obtained.

The DCR01 is a switching power supply and as such can

place high peak current demands on the input supply. In

order to avoid the supply falling momentarily during the fast

switching pulses, ground and power planes should be used

to track the power to the input of DCR01 (this will also serve

to reduce noise on the circuit). If this is not possible, the

supplies must be connected in a star formation, with the

tracks made as wide as possible.

If the SYNC pin is being used, the tracking between device

SYNC pins should be short to avoid stray capacitance. If the

SYNC pin is not being used it is advisable to place a guard

ring (connected to input ground) around this pin to avoid any

noise pick up.

The output should be taken from the device using ground

and power planes. This will ensure minimum losses.

A good quality low ESR capacitor placed as close as

practicable across the input will reduce reflected ripple and

ensure a smooth start up.

A good quality low ESR capacitor placed as close as

practicable across the rectifier output terminal and output

ground will give the best ripple and noise performance.

THERMAL MANAGEMENT

Due to the high power density of this device, it is advisable

to provide a ground plane on the output. The output regula-

tor is mounted on a copper leadframe, and a ground plane

will serve as an efficient heatsink.

DCR 01

OUT

(1)

OUT

= 0.1µF

FILTER

= 1µF

POS

O/P

NEG

O/P

ENABLE

REC

ERROR

SYNC

DCR 01

OUT

(1)

OUT

= 0.1µF

FILTER

= 1µF

ENABLE

REC

ERROR

SYNC

NOTE: (1) 2.2µF capacitor with low ESR for 5V

devices and 0.47µF for 12V and 24V devices.

FIGURE 3. Dual Polarity Voltage Generation from Two Self-Synchronized DCR01’s.

Part #	DCR010503U
Description	DC/DC CONVERTER, 1W REGULATED12PIN SOP -40 to 85
Category	IC
Availability	Out of Stock
Qty	0

DCR010503U

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