VISHAY SEMICONDUCTORS www.vishay.com Optical Sensors Application Note Ambient Light Sensors - Circuit and Window Design Ambient light sensors are used to detect light or brightness in a manner similar to the human eye. They are most commonly found in industrial lighting, consumer electronics, and automotive systems, where they allow settings to be adjusted automatically in response to changing ambient light conditions. By turning on, turning off, or adjusting features, ambient light sensors can conserve battery power and provide extra safety while eliminating the need for manual adjustments. Vishay offers a wide variety of ambient light sensors in leaded and surface mount packages, with photodiode or phototransistor outputs, narrow to broad viewing angles or angles of half sensitivity, and automotive qualified to the AEC-Q101 standard (Table 1). Sensors that are automotive qualified have an “X01” in the part number. TEMD5510FX01 TEMT6200FX01 TEMD6200FX01 TEMD6010FX01 TEMT6000X01 TEP TEPT5600 TEPT4400 TEPT5700 BPW21R P Table 1 PART NUMBER MOUNTING SIZE (mm) PEAK WAVELENGTH (nm) BANDWIDTH (nm) LIGHT LIGHT ANGLE OF CURRENT (2) CURRENT (1) HALF SENSITIVITY STANDARD A FLUORESCENT (μA) (μA) (± °) PHOTODIODE OUTPUT TEMD6010FX01 SMD 2.0 x 4.0 x 1.0 540 430 to 610 60 0.04 TEMD5510FX01 SMD 4.2 x 5.0 x 1.1 540 430 to 610 65 1.00 0.70 TEMD6200FX01 SMD 1.2 x 2.0 x 0.85 540 430 to 610 60 0.04 0.03 Leaded TO5 - 8 mm 565 420 to 675 50 0.90 0.75 SMD 1.2 x 2.0 x 0.85 550 450 to 610 60 12 7 BPW21R 0.03 PHOTOTRANSISTOR OUTPUT TEMT6000X01 SMD 2.0 x 4.0 x 1.0 570 430 to 800 60 50 21 TEPT5700 Leaded 5 mm, flat top 570 430 to 800 50 75 31 TEPT5600 Leaded 5 mm 570 430 to 800 20 350 145 TEPT4400 Leaded 3 mm 570 430 to 800 30 200 83 Notes (1) E = 100 lux, V v CE = 5 V, CIE illuminant A, typical (2) E = 100 lux, V v CE = 5 V, e.g., Sylvania color abbrev. D830, typical Revision: 10-Dec-12 Document Number: 84154 1 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 APPLICATION NOTE TEMT6200FX01 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design FILTERING Most photodiodes and some phototransistors feature an epoxy filter that improves the relative spectral sensitivity to be closer to the sensitivity of the human eye; this is sometimes called the v(λ) curve. Part numbers that contain the letter “F” feature this epoxy. Figure 1 shows an ambient light sensor without the epoxy filter and figure 2 shows the sensor with the epoxy filter. With this epoxy filter the bandwidth (λ0.5) is reduced from 430 nm to 800 nm to 430 nm to 610 nm. 20019 0.9 Relative Spectral Sensitivity S(λ)rel - Relative Spectral Sensitivity 1.0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 300 400 500 600 700 800 900 1000 1100 λ - Wavelength (nm) 1.0 0.8 human eye 0.6 0.4 0.2 0.0 400 20047 Fig. 1 - Graph without Epoxy Filter Photodiode 600 800 1000 Wavelength (nm) Fig. 2 - Graph with Epoxy Filter BINNING Vishay offers phototransistor- and photodiode-based ambient light sensors. For a given irradiance, phototransistors may show lot-to-lot variability of the output current caused by variability of the photosensitivity of the chip and the transistor gain. The lot-to-lot variability of photodiodes is significantly lower because it is caused only by the variability of the photosensitivity. Vishay offers its ambient light sensors with phototransistor output in binned groups (Table 2). These groups cannot be ordered separately but each reel is marked with a label A, B, or C that will allow the user to select the appropriate load resistor to compensate for these wide tolerances. Table 2 - TEMT6200FX01 TYPE DEDICATED CHARACTERISTICS (Tamb = 25 °C, unless otherwise specified) PARAMETER APPLICATION NOTE Photo current Revision: 10-Dec-12 TEST CONDITION EV = 100 lux, CIE illuminant A, VCE = 5 V BINNED GROUP SYMBOL MIN. MAX. UNIT A IPCE 7.5 15 μA B IPCE 12 24 μA C IPCE 19.5 39 μA Document Number: 84154 2 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design CHOOSING THE LOAD RESISTOR In order to minimize the output variability of the 3 V to 5 V sensor, the load resistor (RL) needs to be selected based on the illuminance expected or measured in the application. A typical circuit for operating an ambient light sensor with phototransistor output is shown in Figure 3. For the TEMT6200FX01, the typical output current is 4.6 μA at 20 lux. At 100 lux the output current ranges from 7.5 μA to 39 μA. With the binning mentioned RL = 10 kΩ previously, this 100 lux range is split into three bins. A different load resistor should be used for each bin Fig. 3 so the output is relatively consistent for a given lux level. Let’s assume that the application detection range is from 10 lux to 1000 lux. With a 10 kΩ load resistor, a voltage from 0.023 V to 2.3 V is produced. The photo current based on the voltage equates to 2.3 μA to 230 μA. The goal in choosing the resistor is to have the same output voltage for the mean value of each bin, Table 3. Table 3 PART NUMBER PHOTO CURRENT, IPCE at 100 lux (μA) BIN TEMT6200FX01 MIN. MEAN A 7.5 11.25 MAX. 15 B 12 18.00 24 C 19.5 29.25 39 Table 4 BIN B BIN A BIN C IPCE = 18 μA, RL = 10 kΩ V = 18 μA x 10 kΩ V = 180 mV 0.18 V = 0.00001125 A x RL RL = 0.18 V/0.00001125 A RL = 16 kΩ 0.18 V = 0.00002925 A x RL RL = 0.18 V/0.00002925 A RL = 6.2 kΩ APPLICATION NOTE By changing the resistor based on the bin, the overall tolerance of the TEMT6200FX01 is reduced from a factor of 5 (7.5 to 39) to a factor 2 (e.g. 12 to 24). Revision: 10-Dec-12 Document Number: 84154 3 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design OPERATING FROM 1 lux TO 100 000 lux 10 IPCE - Photo Current (mA) The sensitivity of TEMT6200FX01 allows detection of ambient light from 1 lux to 100 000 lux. In many applications, the detection range of an ambient light sensor is from 1 lux to 1000 lux. The calculations for the load resistor on the previous page were for this range. The maximum allowable current for the TEMT6200FX01 is 20 mA. Extrapolating the graph of the photo current versus illuminance in figure 4, a photo current of 18 mA is approximately equal to 100 000 lux. The relationship between photo current and ambient light is linear. Given the extremely low dark current for this part of 50 nA, and again extrapolating the graph, results in approximately 180 nA of photo current for 1 lux. The output current from 1 lux to 100 000 lux is 180 nA to 18 mA. 1 0.1 VCE = 5 V 0.01 0.001 10 100 20769 1000 10 000 EV - Illuminance (Ix) Fig. 4 - Photo Current vs. Illuminance Depending on the sensitivity of the analog-to-digital converter, an operational amplifier could be placed at the output of the sensor as shown in figure 5. In this case, a load resistor of 10 kΩ results in an output voltage of 2 mV to 2.0 V for an ambient level of 1 lux to 1000 lux. EV = 1 lux to 1000 lux 3 V to 5 V optional, depending on sensitivity of used A/D + A: RL = 16 kΩ B: RL = 10 kΩ C: RL = 6.2 kΩ IPCE = 0.2 μA to 200 μA RL = 10 kΩ Light Meter w.OP-amp: EV: 1 lux to 1000 lux A/D 10 kΩ VRL = (0.2 μA x 10 kΩ) to (200 μA x 10 kΩ) 1 kΩ VRL = 2 mV to 2 V Fig. 5 Operating over the full ambient range of 1 lux to 100 000 lux and using a 1 kΩ load resistor would result in an output voltage from 0.18 mV to 18 V. Given a typical operating voltage of 5 V or less, this circuit design is not adequate. The load resistor will need to switch based on the output of the operational amplifier (figure 6). Switching a low-ohm resistor that is in parallel to the divider resistor to ground when the operational amplifier is above a certain value, for example 3 V, allows full-range operation. 3V APPLICATION NOTE 1 lux to 1000 lux 1000 lux to 100 000 lux IPCE = 180 nA to 180 μA IPCE = 180 μA to 18 mA RL = 100 Ω → RL = 100 Ω VRL = 18 μV to 18 mV VRL = 18 mV to 1.8 V with va = 100 with va = 1 VADC = 1.8 mV to 1.8 V VADC = 18 mV to 1.8 V Light Meter w.OP-amp: EV: 1 lux to 100 000 lux TEMT6200FX01 + RL = 100 Ω A/D - 100 kΩ 100 kΩ 1kΩ Fig. 6 Revision: 10-Dec-12 Document Number: 84154 4 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design APPLICATION SCHEMATICS APPLICATION NOTE Some simple application circuits for ambient light sensors with phototransistor output are shown below. Fig. 7 - Switch, Output High at EV > 25 lux, IPCE: 10 μA, VOUT: 2.0 V, Input Leakage Current: < 1 μA Fig. 10 - Light Meter, EV: 10 lux to 1000 lux, IPCE: 4 μA to 400 μA, VOUT: 16 mV to 1.6 V Fig. 8 - Switch, Output Low at EV > 10 lux, IPCE: 4 μA, Gate Threshold: 2.0 V, Input Leakage Current: < 1 μA Fig. 11 - Low Illuminance Light Meter, EV: 0.1 lux to 10 lux, IPCE: 40 nA to 4 μA, VOUT: 16 mV to 1.6 V Fig. 9 - Light Switch, (Schmitt Trigger), Switch on at EV < 100 lux, IPCE: < 40 μA, Input Leakage Current: < 5 μA Fig. 12 - Light Switch, Switch On at EV < 100 lux IPCE: < 40 μA Revision: 10-Dec-12 Document Number: 84154 5 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design PHOTODIODE-BASED AMBIENT LIGHT SENSORS The basic characteristics of the ambient light sensors with photodiode outputs are shown in Table 5 below. All photodiode-based ambient light sensors have an additional epoxy filter that brings the relative spectral sensitivity close to the v[λ] or “Human Eye” curve. BPW21R comes with a color correction filter in its flat glass window that provides a similar effect. The low photocurrent output requires a noise-free amplification which can be achieved with the appropriate op amp. Examples of noise-free op amps that could be used with the photodiode output devices and related circuitry are shown on the next page. Table 5 - TEMD6010FX01 BASIC CHARACTERISTICS (Tamb = 25 °C, unless otherwise specified) TEST CONDITION SYMBOL MIN. Breakdown voltage PARAMETER IR = 100 μA, E = 0 lux V(BR) 16 Reverse dark current VCE = 10 V, E = 0 lux Diode capacitance TYP. MAX. UNIT Iro 0.1 5 nA VR = 0 V, f = 1 MHz, E = 0 lux CD 60 pF VR = 5 V, f = 1 MHz, E = 0 lux CD 24 pF V λ = 550 nm, VR = 5 V Ira EV = 100 lux, CIE illuminant A, VR = 5 V Ira EV = 100 lux, CIE illuminant A, VR = 5 V TKIra 0.2 %/K Angle of half sensitivity ϕ ± 60 deg Wavelength of peak sensitivity λp 540 Reverse light current Temperature coefficient of Ira Ee = 1 mW/cm2, Range of spectral bandwidth λ0.5 1 0.03 0.04 430 μA 0.09 μA nm 610 nm Compared to phototransistor-based ambient light sensors, the lot-to-lot variability of photodiodes is significantly lower because it is caused only by the variability of the photosensitivity resulting in tolerances of 20 % to 30 %. Variability of the output current of photodiode-based ambient light sensors is also due to chip size. A larger detection area or chip size will result in greater photo current. The TEMD5510FX01 and the BPW21R produce double the current of the TEMD6200FX01 and TEMD6010FX01. The TEMD5510FX01 contains a 7.5 mm2 chip while the size of the sensitive area of the chip in theTEMD6x is just 0.27 mm2. APPLICATION SCHEMATICS FOR PHOTODIODE-BASED AMBIENT LIGHT SENSORS A sensitive, FET-input type of photodiode preamplifier, with a very low input noise, should be used, such as: • Linear Technology LTC6240 • Texas Instruments (OPA827) • Burr-Brown (OPA128) APPLICATION NOTE • Analog Devices (AD549) Fig. 13 - Photodiode Preamp Revision: 10-Dec-12 Fig. 14 - 1M Transimpedance Amplifier with 43 nV/Hz-2 Output Noise Document Number: 84154 6 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design Fig. 15 - Transimedance Amplifier Fig. 16 - Sensitive Photodiode Amplifier WINDOW SIZE If the ambient light sensor will be place behind a window or cover, the window material should be completely transmissive to visible light (400 nm to 700 nm). For optimal performance the window size should be large enough to maximize the light irradiating the sensor. In calculating the window size, the only dimensions that the design engineer needs to consider are the distance from the top surface of the sensor to the outside surface of the window and the size of the window. These dimensions will determine the size of the detection zone. First, the center of the sensor and center of the window should be aligned. Most ambient light sensors have an angle of half sensitivity of ± 60° as shown in figure 17 and 18. 0° 10° 20° 40° 1.0 0.9 50° 0.8 60° 70° 0.7 ϕ - Angular Displacement Srel - Relative Sensitivity APPLICATION NOTE 30° 80° 0.6 0.4 0.2 0 94 8318 Fig. 17 - Relative Sensitivity vs. Angular Displacement Revision: 10-Dec-12 Fig. 18 - Angle of Half Sensitivity, Cone Document Number: 84154 7 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design With the assumption that the detection zone is a cone shaped region with an angle of ± 60°, the following are dimensions for the distance from the top surface of the sensor to the outside surface of the glass, d, and the width of the window, w. Calculation w tan α = x/d x 0.75 α = 60° . D d tan 60° = 1.73 = x/d α x = 1.73 x * d tan 60° = 1.73 x/d = 1.73 x = (1.73)d With the length of the chip equal to 0.75 mm, the width of the window can be calculated: 0.85 w = 0.75 mm + 2 (1.73d) here in drawing α = 60° dimensions in mm Fig. 19 - Angle of Half Sensitivity, Cone Shown below are results for different distances from the sensor to the outside of the window surface. d x CALCULATION w 0.5 0.87 0.75 + 1.74 2.49 1.0 1.73 0.75 + 3.46 4.21 1.5 2.60 0.75 + 5.20 5.95 2.0 3.46 0.75 + 6.92 7.67 2.5 4.33 0.75 + 8.66 9.41 3.0 5.19 0.75 + 10.38 11.13 A smaller window size also could be used. If so, reference measurements should be made if the output is expected to be similar to a light meter. Calculation w tan α = x/d x 0.75 α = 40° . D α tan 40° = 0.84 = x/d x = 0.84 x * d APPLICATION NOTE x = (0.84)d With the length of the chip equal to 0.75 mm, the width of the window can be calculated: 0.85 here in drawing α = 40° tan 40° = 0.84 x/d = 0.84 d w = 0.75 mm + 2 (0.84d) dimensions in mm Fig. 20 - Angle of Half Sensitivity, Cone Shown below are results for different distances from the sensor to the outside of the window surface. d x CALCULATION w 0.5 0.42 0.75 + 0.84 1.59 1.0 0.84 0.75 + 1.68 2.43 1.5 1.28 0.75 + 2.56 3.31 2.0 1.68 0.75 + 3.36 4.11 2.5 2.10 0.75 + 4.20 4.95 3.0 5.52 0.75 + 5.04 5.79 Revision: 10-Dec-12 Document Number: 84154 8 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 Application Note www.vishay.com Vishay Semiconductors Ambient Light Sensors - Circuit and Window Design APPLICATION NOTE TYPICAL ILLUMINANCE VALUES ILLUMINANCE EXAMPLE 10-5 lux Light from Sirius, the brightest star in the night sky 10-4 lux Total starlight, overcast sky 0.002 lux Moonless clear night sky with airflow 0.01 lux Quarter moon 0.27 lux full moon on a clear night 1 lux Full moon overhead at tropical latitudes 3.4 lux Dark limit of civil twilight under a clear sky 50 lux Family living room 80 lux Hallway/toilet 100 lux Very dark overcast day 320 lux to 500 lux Office lighting 400 lux Sunrise or sunset on a clear day 1000 lux Overcast day; typical TV studio lighting 10 000 lux to 25 000 lux Full daylight (not direct sun) 32 000 lux to 130 000 lux Direct sunlight Revision: 10-Dec-12 Document Number: 84154 9 For technical questions, contact: [email protected] THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000