TFBS4711(2006) Просмотр технического описания (PDF) - Vishay Semiconductors

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производитель

TFBS4711
(Rev.:2006)

Serial Infrared Transceiver SIR, 115.2 kbit/s, 2.7 V to 5.5 V Operation

Vishay Semiconductors 

TFBS4711

Vishay Semiconductors

Recommended Circuit Diagram

VCC

IR Controller

Vdd

IRTX

IRRX

IRMODE

Rled

R1= 47Ω

TFBS4711

IREDA (1)

TXD (2)

RXD (3)

SD (4)

Vcc (5)

GND (6)

18510

GND

C1 C2

C3

C4

4.7 μF 0.1μF 4.7 μF 0.1 μF

Figure 3. Recommended Application Circuit

Operated at a clean low impedance power supply the

TFBS4711 needs no additional external components

when the internal current control is used. For reducing

the IRED drive current for low power applications with

reduced range an additional resistor can be used to

connect the IRED to the separate power supply.

Depending on the entire system design and board

layout, additional components may be required. (see

figure 3).

Worst-case conditions are test set-ups with long

cables to power supplies. In such a case capacitors

are necessary to compensate the effect of the cable

inductance. In case of small applications as e.g.

mobile phones where the power supply is close to the

transceiver big capacitors are normally not neces-

sary. The capacitor C1 is buffering the supply voltage

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 optional for

reducing the IRED drive current.

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 when

noisy supply voltage is used or pick-up via the wiring

is expected.

R2, C1 and C2 are optional and dependent on the

quality of the supply voltage VCCX and injected noise.

An unstable power supply with dropping voltage dur-

ing transmission may reduce the sensitivity (and

transmission range) of the transceiver.

The placement of these parts is critical. It is strongly

recommended to position C2 as close as possible to

the transceiver power supply pins.

In any case, when connecting the described circuit to

the power supply, low impedance wiring should be

used.

When extended wiring is used the inductance of the

power supply can cause dynamically a voltage drop

at VCC2. Often some power supplies are not to follow

the fast current rise time. In that case another 10 µF

capacitor at VCC2 will be helpful.

The recommended components in table 1 are for test

set-ups

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 termi-

nation. See e.g. "The Art of Electronics" Paul Horow-

itz, Winfield Hill, 1989, Cambridge University Press,

ISBN: 0521370957

I/O and Software

In the description, already different I/Os are men-

tioned. Different combinations are tested and the

function verified with the special drivers available

from the I/O suppliers. In special cases refer to the I/

O manual, the Vishay application notes, or contact

directly Vishay Sales, Marketing or Application.

Table 1.

Recommended Application Circuit Components

Component

C1, C3

C2, C4

R1

Recommended Value

4.7 µF, 16 V

0.1 µF, Ceramic

47 Ω, 0.125 W

Vishay Part Number

293D 475X9 016B

VJ 1206 Y 104 J XXMT

CRCW-1206-47R0-F-RT1

www.vishay.com

6

Document Number 82633

Rev. 1.9, 07-Nov-06

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