Introduction
The APDS-9003 is a low cost analog-output ambient light photo sensor in miniature chipLED lead-surface mount package. It consists of a spectrally suited photo sensor, which provides excellent responsivity that is close to the response of human eyes.The APDS-9003 is ideal for applications in which the measurement of ambient light is used to control display backlighting. Mobile appliances such as the mobile phones and PDAs that draw heavy current from display backlighting will benefit from incorporating these photo sensor products in their designs by reducing power consumption significantly.
Sensor Characteristics
Features
• Low sensitivity variation across various light sources
• Operating temperature: -400C to 850C
• Vcc supply 2.4 to 5.5V
• ROHS compliant and Lead Free Package
Applications
• Detection of ambient light to control display backlighting
Mobile devices – Mobile phones, PDAs
Computing devices – Notebooks, Webpads
Consumer devices – TVs, Video Cameras,
Digital Still Cameras
• Automatic Residential and Commercial Lighting Management
• Electronic Signs and Signals
Figure 1: Application of sensor in smartphones [2]
As shown in figure 1, the APDS-9003 sensors can be used as Ambient Light Detection sensor. They are responsible for dimming the light with respect to the surroundings light. They are also responsible to black out the screen during a call. This helps to save the power of the device and increase the life of the screen and power source.
Relative Spectral Response vs Wavelength
Figure 2: Relative Spectral Response Vs wavelength[1]
Operating conditions
| Parameter | Symbol | Min | Max | Unit |
|---|---|---|---|---|
| Storage/Operating Temperature | Ts/Ta | -40 | 85 | °C |
| Maximum rating Supply Voltage | Vcc | 0 | 6 | V |
| Operating Supply Voltage | Vcc | 2.4 | 5.5 | V |
Output Specifications
| Parameter | Symbol | MIn. | Typ | Max | Unit | Condition |
|---|---|---|---|---|---|---|
| Output Current | I_OUT1 | 6.3 | 19 | 31 | uA | Vcc=3V, Lux= 10(Illuminance by CIE standard light source) |
| Output Current | I_OUT2 | 90 | 230 | 370 | uA | Vcc=3V, Lux= 100(Flourescent light is used as light source) |
| Output Current | I_OUT3 | - | 276 | - | uA | Vcc=3V, Lux= 100(White LED is used as light source) |
| Dark Current | I_DARK | - | 50 | 160 | nA | Vcc=3V, Lux= 0 |
Sensitivity(Light current ratio) | I_OUT3/I_OUT2 | - | 1.2 | - | - | - |
| Rise Time | Tr | - | 0.95 | 2 | ms | Vcc=3.0V,Lux=100,Rload=1k(White LED is used as light source) |
| Fall Time | Tf | - | 0.8 | 2 | ms | Vcc=3.0V,Lux=100,Rload=1k(White LED is used as light source) |
| Supply Current | Icc | - | 2.5 | - | mA | Vcc=3.0V,Lux=100,Rload=1k(White LED is used as light source) |
| Saturated Output Voltage | Vo | 2.2 | 2.32 | - | V | Vcc=3.0V,Lux=100,Rload=1M(White LED is used as light source) |
| Peak Sensitivity Wavelength | - | 620 | - | nm | ||
| Propagation Delay time | td | - | 600 | - | us | Vcc=3.0V,Lux=100,Rload=1k(White LED is used as light source) |
| Storage Delay time | ts | - | 200 | - | us | Vcc=3.0V,Lux=100,Rload=1k(White LED is used as light source) |
So if we check the figure and the sensitivity the change in wavelength changes the sensitivity response. The change in Lux also changes the current by 1.2. Typically, the white light is used as the source which consists of 3Volts input signal with 100 illuminance. However the output depends on the load ressistor connected with the sensor. As the increase in the illuminance effects the output signal it is better to avoid unwanted lights except the source light.
Interface Electronic circuits
The APDS-9003 is an anlog-output ambient light photo sensor. This photo sensor produces a high gain photo current that can be converted to voltage with a standard value of external resistor. Thus the higher we need the output of the sensor, a higher value resistor can be used to apply it in our electronic circuits with ADC input. Thus with the resistor fixed, the voltage output is dependent on the photo current which is generated by the brightness of the light stone on the photo sensor. Hence increase in the brightness of light and load resistor will increase the output voltage. Hence, We must be sensible in selecting the load resistor in order to determine the amount of current voltage conversion in the circuit.
Inorder to get a typical output voltage of 2.32V, We need to have the 3V input voltage for this sensor. As all the electronic devices, this light sensor also consists of noise to external excess light.
Light sources consists of ac noise frequencies. For example a flourescent light consists of about 100Hz ac noise frequency. A low pass filter is required to be added in the circuit parallel with the load resistor to decrease the ripple.
Figure 3: Electronic configuration for APDS-9003[1]
As shown in figure 3, The 3V Vcc is supplied to the sensor in pin 1 and pins 2 to 5 are not connected. Pin 6 is the output pin. When a light source strikes the sensor it produces photo current. The current through load resistor creates the analog voltage output. The capacitor in parallel with the RL filters the noise and the filtered signal is converted to digital format in our electronic devices using A/D converter or a microcontroller.
References
- APDS-9003, Avago Technologies datasheet
URL: http://www.avagotech.com/docs/AV01-0238EN [Online], Last Accessed: 10.4.2014 - Mobile phones- much more than just telephones, Avago Technologies
URL: http://www.sekorm.com/Ectm/19789 [Online], Last Accessed: 10.4.2014