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VISHAY SEMICONDUCTORS

Optical Sensors

Application Note

Designing the VEML6070 UV Light Sensor

Into Applications

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Revision: 26-Mar-18

Document Number: 84310

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APPLICATION NOTE

By Reinhard Schaar

UV LIGHT SENSOR WITH I

C INTERFACE

The VEML6070 is an advanced ultraviolet (UVA) light sensor designed with a CMOS process and featuring an I

C protocol

interface.

Fig. 1 - Block Diagram of the VEML6070

The VEML6070 is easily operated via a simple I

C command. The active acknowledge (ACK) feature with threshold window

settings allows the UV sensor to send out an UVI alert message. Under a strong solar UVI condition, the smart ACK signal can

be easily implemented by the software programming. The VEML6070 incorporates a photodiode, amplifiers, and analog / digital

circuits into a single chip. The VEML6070’s adoption of Filtron

UV technology provides the best spectral sensitivity to cover

UV spectrum sensing. It has an excellent temperature compensation and a robust refresh rate setting that does not use an

external RC low-pass filter. The VEML6070 shows linear sensitivity to solar UV light, which can easily be adjusted by selecting

the proper external resistor.

The device can be used as a solar UV indicator for handheld cosmetic / outdoor sports products or any kind of consumer

products.

The VEML6070 comes within a very small surface-mount package with dimensions of just 2.35 x 1.8 x 1.0 (L x W x H in mm).

The VEML6070 operates within a supply voltage range of 2.7 V to 5.5 V. The necessary pull-up resistors at the I

C and ACK

lines can be connected to the same supply as the microcontroller, between 1.7 V and 5.5 V.

SCLACK

SDA

GND

SET

UV-PD

VEML6070

Output buffer

C interface

Low-pass

lter

Temperature

sensor

Oscillator

Timing

controller

Summary of content (14 pages)

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VISHAY SEMICONDUCTORS www.vishay.com Optical Sensors Application Note Designing the VEML6070 UV Light Sensor Into Applications By Reinhard Schaar UV LIGHT SENSOR WITH I2C INTERFACE The VEML6070 is an advanced ultraviolet (UVA) light sensor designed with a CMOS process and featuring an I2C protocol interface. VEML6070 GND 1 Temperature sensor 6 VDD 5 SCL 4 RSET Low-pass filter ACK 2 Timing controller SDA Output buffer I2C interface UV-PD 3 Oscillator Fig.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications 1.7 V to 5.5 V R1 R2 R3 Host Micro Controller GND (1) 2.7 V to 5.5 V VDD (6) C1 100 nF VEML6070 R5 RSET (4) SDA (3) I2C bus data SDA SCL (5) I2C bus clock SCL ACK (2) GPIO (INT) 270 kΩ Fig. 2 - Application Circuit The value for the pull-up resistors should be 2.2 kΩ. The supply current of this device is also dependent on the RSET value.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications What does this wavelength mean? To understand this, the diagram below shows that it is in the middle of the so-called UVA region. Ultraviolet UVC 100 UVB 280 Visible Infrared UVA 320 400 700 Wavelength (nm) Fig. 4 - Light Spectrum Visible light has wavelengths between 400 nm and 750 nm. UV light has shorter wavelengths, from 200 nm to 400 nm.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications UVB rays - wavelengths ranging from 280 nm to 320 nm - are extremely energetic and harmful to the skin; they are responsible for 65 % of skin tumors. Thankfully, only 0.1 % of the solar energy that arrives on the earth’s surface is in the form of UVB radiation. UVA rays - wavelengths ranging from 320 nm to 400 nm - are less powerful than UVB rays, but are highly penetrating.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications 0x70 is the only command register where shut-down, integration time, and acknowledge activity settings are handled.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications WHAT VALUES MAY BE SEEN WITH THE VEML6070? If no exact UV light source is available to check the performance of the VEML6070, and only “normal” daylight is being used to study the VEML6070’s response, please note that the UV power is dependent on the time of day, season, and location where the measurements will be performed.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications 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.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications The size of the window is simply calculated according to triangular rules. The dimensions of the device, as well as the sensitive area, are shown within the datasheet. For best results, the distance below the window’s upper surface and the specified angle below the given window diameter (w) are known. 0.1 Pin 1 marking 1 6 0.28 3 4 Dimensions (L x W x H in mm): 2 x 2 x 0.85 w x 0.5 .
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications A smaller window will also be sufficient, although it will reduce the total sensitivity of the sensor. 0.1 Pin 1 marking 1 6 0.28 3 4 Dimensions (L x W x H in mm): 2 x 2 x 0.85 w x 0.5 . D d tan 40° = 0.84 = x/d x = 0.84 x d α 0.85 Here in drawing, α = 40° Dimensions in mm Fig.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications VEML6070 SENSOR BOARD AND DEMO SOFTWARE The small blue VEML6070 sensor board fits to the SensorXplorerTM demonstration kit. Please also see: www.vishay.com/optoelectronics/SensorXplorer. With the help of the VEML6070 sensor board and the demo software, one can easily test the UV sensor. Four possible integration times are selectable.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications WORD i; for (i = 0; i < 4; i++) { if (uvs_step <= risk_level_mapping_table[i]) { break; } } return (RISK_LEVEL)i; } int VEML6070_read_byte(WORD addr, BYTE *data) { int err = 0; int retry = 3; struct i2c_msg msg; // Read byte data msg.addr = addr; msg.flags = I2C_M_RD; msg.len = 1; msg.
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Application Note www.vishay.com Vishay Semiconductors Designing the VEML6070 UV Light Sensor Into Applications THE VEML6070’S ACK SIGNAL The VEML6070 features a function for sending an acknowledge signal (ACK) to the microcontroller when the UV value changes are bigger than one of two pre-programmable step sizes: ACK_THD. The purpose of the ACK signal is similar to an interrupt feature, which informs the μC once the sensed data level goes below or beyond the interrupt threshold setting.