DCP02 datasheet(8/17 Pages) TI

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APPLICATION INFORMATION

OPTIMIZING PERFORMANCE

TRANSFORMER DRIVE CIRCUIT

SELF-SYNCHRONIZATION

PCB Design

DCP02 Series

SBVS011K – MARCH 2000 – REVISED FEBRUARY 2008

The DCP01B, DCV01, and DCP02 are three families

of miniature DC/DC converters providing an isolated

unregulated voltage output. All are fabricated using a

Optimum performance can only be achieved if the

CMOS/DMOS process with the DCP01B replacing

device is correctly supported. The very nature of a

the familiar DCP01 family that was fabricated from a

switching converter requires power to be instantly

bipolar

process.

The

DCP02

essentially

available when it switches on. If the converter has

extension of the DCP01B family, providing a higher

DMOS switching transistors, the fast edges will create

power output with a significantly improved load

a high current demand on the input supply. This

regulation. The DCV01 is tested to a higher isolation

transient load placed on the input is supplied by the

voltage.

external input decoupling capacitor, thus maintaining

the input voltage. Therefore, the input supply does

not

see

this

transient

(this

analogy

high-speed digital circuits). The positioning of the

Transformer drive transistors have a characteristically

capacitor is critical and must be placed as close as

low value of transistor on resistance (RDS); thus, more

possible to the input pins and connected via a

power

transferred

the

transformer.

The

low-impedance path.

transformer drive circuit is limited by the base current

available to switch on the power transistors driving

The optimum performance primarily depends on two

the transformer and the characteristic current gain

factors:

(beta),

resulting

slower

turn-on

time.

1. Connection of the input and output circuits for

Consequently, more power is dissipated within the

minimal loss.

transistor, resulting in a lower overall efficiency,

2. The ability of the decoupling capacitors to

particularly at higher output load currents.

maintain the input and output voltages at a

constant level.

The input synchronizations facility (SYNCIN) allows

for easy synchronizing of multiple devices. If two to

The copper losses (resistance and inductance) can

eight

devices

(maximum)

have

their

respective

be minimized by the use of mutual ground and power

SYNCIN pins connected together, then all devices will

planes (tracks) where possible. If that is not possible,

be synchronized.

use wide tracks to reduce the losses. If several

devices are being powered from a common power

Each device has its own onboard oscillator. This

source, a star-connected system for the track must

oscillator is generated by charging a capacitor from a

be deployed; devices must not be connected in

constant current and producing a ramp. When this

series, as this will cascade the resistive losses. The

ramp passes a threshold, an internal switch is

position of the decoupling capacitors is important.

activated that discharges the capacitor to a second

They must be as close to the devices as possible in

threshold before the cycle is repeated.

order to reduce losses. See the PCB Layout section

When several devices are connected together, all the

for more details.

internal capacitors are charged simultaneously.

When one device passes its threshold during the

charge cycle, it starts the discharge cycle. All the

other devices sense this falling voltage and, likewise,

initiate a discharge cycle so that all devices discharge

together. A subsequent charge cycle is only restarted

when the last device has finished its discharge cycle.

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