EPC120 EPC [Espros Photonics corp], EPC120 Datasheet - Page 5

• Manufacturer Part Number: EPC120
• Description: Fully integrated Light-Barrier Chips with 2-Wire Bus Interface
• Manufacturer: EPC [Espros Photonics corp]

1. Application Information
2. Hardware Design Information
Design Precautions
Ambient Light
© 2011 ESPROS Photonics Corporation
Characteristics subject to change without notice
The epc120 chip set is a general purpose CMOS integrated circuit for light barrier applications. Up to 1023 devices may be connected to two
respectively four wires in parallel. Each device can be individually addressed by an epc100 chip which acts as the interface between a
microcontroller and the 2-wire bus. It manages the bus traffic between the microcontroller and the individual epc120 elements. Programmable
fuses i.e. for the address, sensitivity, LED light pulse width, etc. allow the device to be parametrized in the final system (OTP memory).
The bus controller activates the emitting side of the epc120 and reads the status of the levels at the photodiode input. The status of the
answers to the interface chip can be 'no light pulse received', 'low level light pulse received' and 'high level light pulse received'.
Each chip can be put into 'standby mode' or 'operating mode' to reduce power consumption. During 'standby mode', power consumption is
reduced and the photo diode is shorted. In the 'operation mode', the device is active and ready to receive a light pulse generated by an LED
activated by the LED pin. During a scan, the bus controller addresse s one device after the other and fetches the light barrier status.
This manual describes the various operation and programming modes in order to use epc120. For the interface chip epc100 please refer to
the epc10x “Reference Manual”.
Figure 2 shows the epc120 as an example in a long range light barrier application as a single bus module in a bus-chain configuration with
minimal part count. The LED emits a light pulse when the chip is addressed by the bus controller. Light of the LED is reflected from a
reflecting object or a retro reflector back to the photo diode PD. If the received light is strong enough it triggers the internal thresholds
OUTN/H. The status of the receiver result can be read by the bus controller.
The output to drive the LED is a current source capable to drive typically 1mA. For a high performance light barrier, an LED peak current of
up to 2A is needed. To generate such a high LED current, an external amplifier is necessary. The circuitry in Figure 2 is a simple
implementation of such an amplifier. The complementary Darlington circuit with T1 and T2 and R2 and R3 does the job. In order to avoid
interference on the supply voltage, the supply is isolated (filtered) with R1 and C1. The high peak LED pulse current is delivered by the
capacitor C1, which itself is charged more or less constantly by R1. Make sure, that there is no coupling of the high LED current to the ground
and the supplies of the epc120 or to the cathode of the photo diode. This driver amplifier operates with a VDD
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 3. 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, epc120) shall be a polygon connected to GND to
shield the circuit from the back side as well.
Photodiode DC current can be generated by ambient light, e.g. sun light. DC currents at pin PD do not generate a DC output signal. However,
if I
PDDC
is above the stated maximal value, the input is saturated which blocks the detection of AC current pulses.
1
st
VDD Track for LEDs
VDD for 2-Wire Bus (Data & Power)
GND 2-Wire Bus (Data & Power)
GND Track for LEDs
Bus Module
Figure 2: Long range light barrier chain application with minimal part count
100nF
C3
C4
4.7nF
PD
i.e.
epc300
PD
VDD33
VDD18
epc120
VDD
GND
LED/SCK
CS
SO
SI
5
T1
BC846
R2
10k
T2
BC807-40
IR LED, i.e.
TSML1000
R3
2R2
C1
100μF
Low ESR
R1
100R
LED
Figure 3: Recommended EMC
in a range of 5 to 30 VDC.
Datasheet epc12x - V2.1
n
Module
th
shield
Bus
www.espros.ch
epc120