TFBS4652 Datasheet, PDF (7/13 Pages) Vishay Siliconix – Infrared Transceiver 9.6 kbit/s to 115.2 kbit/s (SIR)

TFBS4652
Vishay Semiconductors
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.
V_CC2
V_logic
V_CC1
GND
SD
TXD
RXD
R1
R2
C1
C2
IRED Anode
V_logic
V_CC
Ground
SD
TXD
RXD
19289
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
at V_CC2. Often some power supplies are not apply to
follow the fast current is rise time. In that case another
10 µF cap at V_CC2 will be helpful.
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
Component
C1, C2
R1
R2
Recommended Value
0.1 µF, Ceramic, Vishay part#
VJ 1206 Y 104 J XXMT
See table 3
47 Ω, 0.125 W (V_CC1 = 3 V)
Figure 1. Recommended Application Circuit
The capacitor C1 is buffering the supply voltage V_CC2
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 depend on the quality of the supply voltages V_CCx
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
Table 3.
Recommended resistor R1 [Ω]
V_CC2
[V]
2.7
3.0
3.3
Minimized current consumption,
IrDA Low power compliant
24
30
36
Document Number 84671
Rev. 1.1, 03-Jul-06
www.vishay.com
137