TFDS4400 データシートの表示（PDF） - Vishay Semiconductors
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TFDS4400 Datasheet PDF : 14 Pages
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TFDS4400
Vishay Semiconductors
The sensitivity control (SC) pin allows the minimum
detection irradiance threshold of the transceiver to be
lowered when set to a logic HIGH. Lowering the
irradiance threshold increases the sensitivity to
infrared signals and increases transmission range up
to 3 meters. However, setting the Pin SC to logic HIGH
also makes the transceiver more susceptable to
transmission errors due to an increased sensitivity to
fluorescent light disturbances. It is recommended to
set the Pin SC to logic LOW or left open if the increased
range is not required or if the system will be operating
in bright ambient light.
The guide pins on the side-view and top-view pack-
ages are internally connected to ground but should not
be connected to the system ground to avoid ground
loops. They should be used for mechanical purposes
only and should be left floating.
Shutdown
The internal switch for the IRED in Vishay SIR
transceivers is designed to be operated like an open
collector driver. Thus, the Vcc2 source can be an
unregulated power supply while only a well regulated
power source with a supply current of 1.3 mA
connected to VCC1/SD is needed to provide power to
the remainder of the transceiver circuitry in receive
mode. In transmit mode, this current is slightly higher
(approximately 4 mA average at 3 V supply current)
and the voltage is not required to be kept as stable as
in receive mode. A voltage drop of VCC1 is acceptable
down to about 2.0 V when buffering the voltage directly
from the Pin VCC1 to GND see figure 3.
This configuration minimizes the influence of high
current surges from the IRED on the internal analog
control circuitry of the transceiver and the application
circuit. Also board space and cost savings can be
achieved by eliminating the additional linear regulator
normally needed for the IRED’s high current
requirements.
The transceiver can be very efficiently shutdown by
keeping the IRED connected to the power supply VCC2
but switching off VCC1/SD. The power source to
VCC1/SD can be provided directly from a
microcontroller (see figure 6). In shutdown, current
loss is realized only as leakage current through the
current limiting resistor to the IRED (typically 5 nA).
The settling time after switching VCC1/SD on again is
approximately 50 ms. Vishay TOIM3232
interface circuit is designed for this shutdown feature.
The VCC_SD, S0 or S1 outputs on the TOIM3232 can
be used to power the transceiver with the necessary
supply current.
If the microcontroller or the microprocessor is unable
to drive the supply current required by the transceiver,
a low–cost SOT23 pnp transistor can be used to switch
voltage on and off from the regulated power supply
(see figure 7). The additional component cost is
minimal and saves the system designer additional
power supply costs.
As external filter, only a capacitor is recommended.
IIRED
Power
Supply
+
– Regulated Power Supply
50 mA
Microcontroller or
Microprocessor
IS
20 mA
R1
IRED
Anode
VCC1/SD
TFDU4100 (Note: Typical Values Listed)
Receive Mode
@ 5 V: IIRED = 210 mA, IS = 1.3 mA
@ 2.7 V: IIRED = 210 mA, IS = 1.0 mA
Transmit Mode
@ 5 V: IIRED = 210 mA, IS = 5 mA (Avg.)
@ 2.7 V: IIRED = 210 mA, IS = 3.5 mA (Avg.)
14878
Figure 6.
IIRED
Power +
Supply – Regulated Power Supply
R1
50 mA
Microcontroller or
Microprocessor
20 mA
IRED
Anode
IS
VCC1/SD
TFDU4100 (Note: Typical Values Listed)
Receive Mode
@ 5 V: IIRED = 210 mA, IS = 1.3 mA
@ 2.7 V: IIRED = 210 mA, IS = 1.0 mA
Transmit Mode
@ 5 V: IIRED = 210 mA, IS = 5 mA (Avg.)
@ 2.7 V: IIRED = 210 mA, IS = 3.5 mA (Avg.)
14879
Figure 7.
Document Number 82524
Rev. A1.5, 31-May-00
www.vishay.com
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