TFBS4652

Document Number 84671

Rev. 1.1, 03-Jul-06

Vishay Semiconductors

www.vishay.com

137

Recommended Circuit Diagram

Operated at a clean low impedance power supply the

TFBS4652 needs only one additional external com-

ponent when the IRED drive current should be mini-

mized for minimum current consumption according

the low power IrDA standard. When combined opera-

tion in IrDA and Remote Control is intended no cur-

rent limiting resistor is recommended. When long

wires are used for bench tests, the capacitors are

mandatory for testing rise/fall time correctly.

and eliminates the inductance of the power supply

line. This one should be a small ceramic version or

other fast capacitor to guarantee the fast rise time of

the IRED current. The resistor R1 is necessary for

controlling the IRED drive current when the internally

controlled current is too high for the application.

Vishay transceivers integrate a sensitive receiver and

a built-in power driver. The combination of both needs

a careful circuit board layout. The use of thin, long,

resistive and inductive wiring should be avoided. The

inputs (TXD, SD) and the output RXD should be

directly (DC) coupled to the I/O circuit.

The capacitor C2 combined with the resistor R2 is the

low pass filter for smoothing the supply voltage.

As already stated above R2, C1 and C2 are optional

and injected noise. An unstable power supply with

dropping voltage during transmission may reduce the

sensitivity (and transmission range) of the trans-

ceiver.

The placement of these parts is critical. It is strongly

recommended to position C2 as close as possible to

the transceiver power supply pins.

When connecting the described circuit to the power

supply, low impedance wiring should be used.

In case of extended wiring the inductance of the

power supply can cause dynamically a voltage drop

follow the fast current is rise time. In that case another

Keep in mind that basic RF-design rules for circuit

design should be taken into account. Especially

longer signal lines should not be used without termina-

tion. See e.g. "The Art of Electronics" Paul Horowitz,

Wienfield Hill, 1989, Cambridge University Press,

ISBN: 0521370957.

Table 2.

Recommended Application Circuit Components

Table 3.

Recommended resistor R1 [

Ω]

Figure 1. Recommended Application Circuit

IRED Anode

V

CC

Ground

V

CC2

V

CC1

GND

SD

TXD

RXD

SD

TXD

RXD

R1

R2

C1

C2

V

logic

V

logic

19289

Component

Recommended Value

C1, C2

0.1 µF, Ceramic, Vishay part#

VJ 1206 Y 104 J XXMT

R1

See table 3

R2

47

Ω, 0.125 W (V

[V]

Minimized current consumption,

IrDA Low power compliant

2.7

24

3.0

30

3.3

36