TFBS5700 Datasheet, PDF (7/14 Pages) Vishay Siliconix – Fast Infrared Transceiver Module (MIR, 1.152 Mbit/s) for IrDA® and Remote Control Applications

TFBS5700
Vishay Semiconductors
Recommended Circuit Diagram
Operated at a clean low impedance power supply the
TFBS5700 needs only one additional external com-
ponent for setting the IRED drive current. However,
depending on the entire system design and board lay-
out, additional components may be required (see
figure 1).
V cc2
V cc1
GND
SD
TXD
RXD
R1
R2
C1
C2
IRED Anode
V cc
Ground
SD
TXD
RXD
19297
Figure 1. Recommended Application Circuit
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 only necessary for
setting 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.
R2, C1 and C2 are optional and dependent on the
quality of the supply voltages VCCx and injected
noise. An unstable power supply with dropping volt-
age during 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 addition, 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_CC2. Often some power supplies are not able to
follow the fast current is rise time. In that case another
10 µF (type, see table under C1) at V_CC2 will be help-
ful.
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, Wienfield Hill, 1989, Cambridge University Press,
ISBN: 0521370957.
Table 2.
Recommended Application Circuit Components
Component
C1, C2
R1
R2
Recommended Value
0.1 µF, Ceramic
Vishay part# VJ 1206 Y 104 J XXMT
2.9 V to 5.4 V supply voltage V_CC2: add a
resistor in series, e.g. 4.7 Ω
47 Ω, 0.125 W (V_CC1 ≥ 2.5 V)
www.vishay.com
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Document Number 84670
Rev. 2.1, 25-Sep-06