EPC100 Datasheet, PDF (6/9 Pages) Espros Photonics corp – Light-Curtain Device with 2-Wire Bus Interface

epc100
Application Information
Schematic Circuit of one Node
Figure 5 shows the schematic circuit of one node on a light curtain system. A node consists of four components only: The receiver chip ep -
c100, a photo diode and two supply voltage decoupling capacitors.
2-wire bus: positive terminal
VDD
epc100
VDD33
PD
VDD18
C1
PD
C2
GND
2-wire bus: negative terminal
Figure 5: Schematic circuit of one node
Recommended Components Values
PD: PIN photo diode, i.e., epc300, epc310, epc320, epc330 (refer to the separate available data sheet epc3xx), or similar
C1: 100nF ceramic capacitor
C2: 4.7nF ceramic capacitor
Design Precautions
The sensitivity at pin PD is very high in order to achieve a long operation range of light curtains even without lenses in
front of the IR LED and/or the photo diode. Thus, the pin PD is very sensitive to EMI. Special care should be taken to
keep the PCB track at pin PD to the photo diode as short as possible (a few mm only!). This track should be kept
away from sources emitting electromagnetic noise which may induce unwanted signals. It is strongly recommended to
cover the chip and the photodiode with a metal shield. A recommended part is shown in Figure 6.
The pins at the bottom are to solder the shield to the PCB with electrical connection to GND. The hole in the front is
the opening window for the photo diode. The back side of the PCB below the sensitive area (PD, epc100) shall be a
polygon connected to GND to shield the circuit from the back side. The capacitors shall be of high mechanical stability
(no piezoelectric effect) in order to avoid unwanted voltage modulation by mechanical shock or vibration.
Figure 6: Recommen-
ded EMC shield
Ambient Light
Photodiode DC current is generated by ambient light, e.g. sun light. DC currents at pin PD do not generate an output signal. However, if I PDDC
is above the stated value, the input is saturated which blocks the detection of AC current pulses.
Photodiode Capacitance
If the photodiode capacitance is below the specified value, the system becomes more sensitive to power supply ripple voltage at higher fre -
quencies (>200kHz). This sensitivity can be reduced by a parallel capacitor to the photodiode. However, this measure reduces the detection
sensitivity. If the photo diode capacity is above the specified value, a lower detection sensitivity and a higher sensitivity spread results.
© 2011 ESPROS Photonics Corporation
6
Characteristics subject to change without notice
Datasheet epc100 - V2.1
www.espros.ch