TFBS4711 Vishay, TFBS4711 Datasheet - Page 6

• Manufacturer Part Number: TFBS4711
• Description: Serial Infrared Transceiver Sir, 115.2 Kbit/s, 2.7 V To 5.5 V Operation
• Manufacturer: Vishay

TFBS4711
Vishay Semiconductors
Recommended Circuit Diagram
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,
Table 1.
Recommended Application Circuit Components
www.vishay.com
6
Component
V CC
IR Controller
18510
C1, C3
C2, C4
R1
Figure 3. Recommended Application Circuit
IRMODE
IRRX
Vdd
IRTX
GND
4.7 μF
C1
0.1μF
C2
R1= 47Ω
Rled
4.7 μF
C3
Recommended Value
0.1 μF
C4
0.1 µF, Ceramic
47 Ω, 0.125 W
4.7 µF, 16 V
IREDA (1)
TXD
RXD
SD
Vcc
GND
TFBS4711
(2)
(3)
(4)
(5)
(6)
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 V
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 V
the fast current rise time. In that case another 10 µF
capacitor at V
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.
CC2
. Often some power supplies are not to follow
CC2
will be helpful.
CRCW-1206-47R0-F-RT1
VJ 1206 Y 104 J XXMT
Vishay Part Number
293D 475X9 016B
CCX
Document Number 82633
and injected noise.
Rev. 1.9, 07-Nov-06