TSSP57P38
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Vishay Semiconductors
Rev. 2.2, 30-Mar-2021
5
Document Number: 82480
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The typical application of the TSSP57P38 is a reflective sensor with analog information contained in its output. Such a sensor
is evaluating the time required by the AGC to suppress a quasi continuous signal. The time required to suppress such a signal
is longer when the signal is strong than when the signal is weak, resulting in a pulse length corresponding to the distance of an
object from the sensor. This kind of analog information can be evaluated by a microcontroller. The absolute amount of reflected
light depends much on the environment and is not evaluated. Only sudden changes of the amount of reflected light, and
therefore changes in the pulse width, are evaluated using this application.
Example of a signal pattern:
Example for a sensor hardware:
There should be no common window in front of the emitter and receiver in order to avoid crosstalk by guided light through the
window.
The logarithmic characteristic of the AGC in the TSSP57P38 results in an almost linear relationship between distance and pulse
width. Ambient light has also some impact to the pulse width of this kind of sensor, making the pulse shorter.
Optical signal
Response of the
TSSP57P38
(strong reflection)
t
repeat
= 500 ms
t
pi
= 120 ms, 38 kHz
Response of the
TSSP57P38
(weak reflection)
Emitter
T
S
AL6200
IR Receiver
T
SS
P57P38
S
eparation to avoid
cro
ss
talk by
s
tray light in
s
ide
the hou
s
ing
