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

The epc112 device is designed to operate at 3.3V power supply (VDD and VDD33).

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11.01.2011

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OUTH

LED

OUTN

PD

VDD33

VDD

epc112

GND

VDD18

R2

13R

C1

10μF

Low ESR

GND

+3.3V

VDD

LED

= +12V

OUTH

OUTN

PD

epc300

R4

3k6

R3

10k

R1

47R

C3 100nF

C2 1μF

C5 4.7nF

C4 100nF

R5

12k

R7

10k

R6

4k7

Marked conductors must be short and low ohmic

IR LED

TSML1000

T1

BC846B

T2

BC846B

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

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,

Photodiode Capacitance

If the photo diode capacity is above the specified value, a lower detection sensitivity and a possible higher sensitivity spread results.

© 2011 ESPROS Photonics Corporation

Characteristics subject to change without notice

10

Datasheet epc111_112 - V2.2

www.espros.ch

Figure 12: Recommended EMC

shield