413101

413101 Visible Light Detector with Analog and Digital Outputs DESCRIPTION The 413101 is a low cost 4-pin visible light sensor, with a current output which is directly proportional to the light level. It has a built in optical filter to provide a response which is close to the human eye, or “photopic”. It also has a digital output to provide on/off switching, with hysteresis to prevent flicker. The output current can be converted to a voltage by connecting it in series with a resistor. The dynamic range is determined by the external resistor and power supply (e.g. 10K and 5V gives a range of 0 to over 250 Lux, but can be up to 1000 lux with a 1K resistor). The internal dark current cancellation enables high accuracy over the full temperature range, even at low light levels. FEATURES • • • • • • • • • • Near human eye photopic response High IR rejection – integrated optical filter Current output highly linear vs light level 1uA per lux current output External resistor sets linear lux range Temperature stable Integrated high gain photo-current amplifier Dark-current cancellation Digital output for on/off switching Hysteresis to prevent flicker close to switching threshold APPLICATIONS • • • • Dawn/dusk sensing Security lighting Night-lights LCD backlight control 1.0 Basic application & test circuit Figure A Supply The 413101 is supplied as probed wafers.Failing die are marked with black ink-dots. VDD 413101 ADJ VADJ RSS DIG_OUT VSS On/Off Signal Pin Description VDD – Positive supply ADJ – Adjust (analog output) VSS – Ground DIG_OUT – Digital output (on/off signal) Preliminary Datasheet Revision A Page 1 of 12 This document is the property of Semefab (Scotland) Ltd and is furnished in confidence and upon the condition that it is neither copied nor released to a third party without prior consent. 413101 Visible Light Detector with Analog and Digital Outputs 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. Preliminary Datasheet Revision A Page 2 of 12 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. 413101 Visible Light Detector with Analog and Digital Outputs Figure B – Block Diagram 3.0 ABSOLUTE MAXIMUM RATINGS PARAMETER Supply input voltage Supply current Operating Temperature, TO Storage Temperature, TS RATING -0.3 to 10 Internally limited -40C to +85C -40C to +100C UNITS V mA °C °C Preliminary Datasheet Revision A Page 3 of 12 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. 413101 Visible Light Detector with Analog and Digital Outputs 4.0 ELECTRICAL SPECIFICATION The following parameters apply over the operating temperature range –40oC to +85 oC, and with RSS=10 K-Ohms and VDD= 5V, as per figure A. Parameter Infra Red response Minimum operational voltage ADJUST current Symbol Test conditions 900nm Min Typ 1 1.8 1.3 300 100 10 30 Lux With 20 Lux illumination on the sensor IADJ = 20uA, Using formula (1) above, R1 = 25K. R3 limits the current flow to the gate of the SCR. This circuit should be suitable for logic SCRs however the gate current should not be too high or it will hold down the VDD supply. LED Drivers FIG2A shows how the 413101 can be used to drive an LED. The output of the ASIC switches high and the LED is switched ON when the light level on the sensor generates a voltage on ADJ pin < VLH. R2 limits the base current into TR1. R3 sets the LED current according to the supply voltage. In this circuit, TR1 can be a low cost switching transistor because the 413101 output is a logic signal. The switching thresholds VLH and VHL are controlled by R1. At the lower threshold VLH : IADJ * R1 = 0.1 * VDD At the upper threshold VHL : IADJ * R1 = 0.15 * VDD It is assumed in the following example that IADJ = 1uA/lux. This will vary depending on the location and the use of lenses etc. Example :VDD = 5V. The lower threshold will be 30 lux, and the upper threshold will be 45 lux. 30 Lux will provide 30uA at the ADJ pin. 0.1 * VDD = 0.5 30uA * R1 = 0.5 R1 = 16.6K (nearest standard value = 18K) FIG 2B . In this circuit the LED will switch ON when light on the sensor is higher than VHL and switch off when the light on the sensor is lower than VLH. The PNP transistor TR1 switches ON when the ASIC output is low. Preliminary Datasheet Revision A Page 9 of 12 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. 413101 Visible Light Detector with Analog and Digital Outputs Relay Driver Fig 3A. The 413101 has a push-pull output (DIG_OUT) which switches high when the light is below VLH. DIG_OUT can source approximately 2mA with a 5V supply. R2 limits the base current into TR1. The switch ON threshold is calculated from IADJ * R1 = 0.1 * VDD , where IADJ = 1uA/lux The switch off threshold is calculated from IADJ * R1 = 0.15 * VDD The max value of IADJ is limited by R1 Fig 3B In this circuit the relay coil is energised when the DIG_OUT pin of 413101 is low. This will happen when the illumination > VHL Interface Circuit Examples Fig 4A shows a possible interface to a microprocessor circuit. The analogue output from the ADJ pin is connected to an A/D input port of the micro. The voltage across R1 will vary linearly with the light level. Without a lens, the source current from the ADJ pin is approximately 1uA/Lux so if R1 = 10K, the voltage at the A/D input will vary at 10mv/lux. The analogue port of the micro can then be programmed to read the light level at the sensor. The digital output from the ASIC is connected to a digital input port of the micro, which would allow the port to sense when the light changes between the upper and lower switching thresholds. Typical applications with a microprocessor input could be to control the backlight for the display of a laptop computer or mobile phone. Fig 4B. The 413101 has a push- pull CMOS digital output which allows it to interface directly to CMOS logic. The OUT pin is high when the voltage at ADJ < 0.1*VDD. The OUT pin is low when the voltage at ADJ is > 0.15VDD. Preliminary Datasheet Revision A Page 10 of 12 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. 413101 Visible Light Detector with Analog and Digital Outputs 413101 413101 413101 413101 413101 Preliminary Datasheet Revision A Page 11 of 12 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. 413101 Visible Light Detector with Analog and Digital Outputs 413101 413101 Preliminary Datasheet Revision A Page 12 of 12 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.