EPC111_17 Datasheet, PDF (10/14 Pages) Espros Photonics corp – Fully integrated standalone light barrier driver & receiver

epc111/112
High speed detection rate design
Figure 11 shows the epc 112 as an example in a high speed detection rate light barrier application with minimal part count. This design is
optimized for a fast reading of light beam interruptions. Whereas the working principle is similar to the above example. This driver circuit
operates with a VDDLED in a range of 6 to 20 VDC.
The epc112 device is designed to operate at 3.3V power supply (VDD and VDD33).
C2 1μF
C3 100nF
+3.3V
C4 100nF
C5 4.7nF
PD
epc300
VDD
epc112
VDD33
VDD18
LED
PD
OUTN
OUTH
GND
VDD = +12V
LED
R5
R9
10k
10k
R7
12k
R6
3k6
T3
BC846B
T2
BC856
R3
10k
IR LED
TSML1000
T1
BC846B
R8
R4
R2
4k7
1k
13R
R1
47R
C1
10μF
Low ESR
GND
OUTN
OUTH
Marked conductors must be short and low ohmic
C2 The epc112 device with its very sensitive input PD needs a well decoupled power supply
Figure 11: High speed detection rate light barrier application with minimal part count
Notice:
The schematic is for illustrating the basic circuit idea only. For the real built up the designer has to take all other additional influence factors in
consideration too eg. design rules, power rating, heat dissipation, ...
Design Precautions: EMC shielding
The sensitivity at pin PD is very high in order to achieve a long operation range of light barriers 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 as short as possible (a few mm only!). This track should be
kept away from the IR LED signal tracks and from other sources which may induce unwanted signals. It is
strongly recommended to cover the chip, the photodiode and all passive components around the chip with a
metal shield. A recommended part is shown in Figure 12. 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 backside of the PCB below the sensitive area (PD, epc111 or epc112) shall be a polygon connected to
Figure 12: Recommended EMC
shield
GND to shield the circuit from the backside as well.
Ambient Light
Photodiode DC current can be generated by ambient light, e.g. sunlight. DC current at pin PD does not generate a DC output signal. However,
if IPDDC is above the stated maximal value, the input is saturated. This blocks the detection of AC current pulses.
Photodiode Capacitance
If the photo diode capacity is above the specified value, a lower detection sensitivity and a possible higher sensitivity spread results.
© 2013 ESPROS Photonics Corporation
10
Characteristics subject to change without notice
Datasheet epc111_112 - V2.5
www.espros.ch