413101 datasheet(2/12 Pages) ETC2

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413101

Visible Light Detector with Analog

and Digital Outputs

Preliminary Datasheet

Revision A

This document is the property of Semefab (Scotland) Ltd. And is furnished in

confidence and upon the condition that it is neither copied or released to a third

party without prior consent.

Page 2 of

2.0 FUNCTIONAL DESCRIPTION

Refer to the block diagram Figure B.

Light falling on the 413101 is converted to current by the photodiode PD1. PD2 is also a photodiode

but it is covered by a metal layer so that it will not respond to light. At normal temperatures the dark

current is very low, however at high temperatures without the dark current cancelling circuit it would

become a significant source of error especially at low light levels. The dark current from PD2 is

subtracted from the dark current and photo-current of PD1, the resultant current is multiplied by a

linear high gain current amplifier and the multiplied current is available as source current from the

ADJ pin. The photodiodes are covered by a multi-layer optical filter, which removes the IR light. With

this optical filter the 413101 has an approximately “eye like” or photopic spectral response.

The primary function of the 413101 is to convert light to an output current at ADJ pin. The

source current from the ADJ pin is proportional to the illumination on the device, at approximately

1uA per Lux. The 413101 has additional circuits to provide a digital ON/OFF output at the DIG_OUT

pin in response to the voltage at the ADJ pin. The current out of the ADJ pin will normally be

converted to a voltage by a resistor between ADJ and ground. A 10K resistor would provide a

10mV/lux output voltage at the ADJ pin. The internal resistor chain sets threshold voltages at the

inputs of the comparators COMP1 and COMP2. The positive input of COMP1 is set to 0.15*VDD and

the negative input of COMP2 to 0.1* VDD. When the voltage on the ADJ pin is less than 0.1*VDD the

flip-flop (U1/U2) is set and the DIG_OUT pin is switched high. When the voltage on the ADJ pin is

higher than 0.15* VDD, the flip-flop is reset and the DIG_OUT pin is switched low. This “hysteresis”

prevents flickering of lamps or chattering of relays when the light level at the sensor is close to the

switching threshold.

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