Vishay VEML3235 Ambient Light Sensor Overview

Summary

Vishay VEML3235 ambient light sensor is a low-power, high-sensitivity device with an I2C interface, implemented using CMOS process. The sensor integrates a photodiode, amplifier, and analog circuitry on a single chip and is controlled via simple I2C commands. Its spectral response closely matches human eye response. The VEML3235/VEML3235SL offer temperature compensation, reliable refresh-rate settings without external RC low-pass filters, high dynamic detection resolution, and a software shutdown mode. Typical applications include handheld devices, notebook computers, consumer electronics, industrial and medical equipment, computing devices, and displays.

Features

• Surface-mount package type
• Integrated module:
  • Ambient light sensor (ALS)
• Supply voltage VDD: 2.6 V to 3.6 V
• Communication via I2C interface
• I2C bus pull-up voltage range: 1.7 V to 3.6 V
• Floor life: 168 h, MSL 3, per J-STD-020
• Low standby current: 1 μA (typical)
• Dimensions (L × W × H):
  • VEML3235: 2 mm × 2 mm × 0.87 mm
  • VEML3235SL: 2.95 mm × 1.5 mm × 1.5 mm

Block Diagram and Typical Application

1. Product Overview and Technical Features

The Vishay VEML3235 is a high-precision ambient light sensor in a miniature transparent 2 mm × 2 mm package, designed for accurate light measurement. The sensor integrates a high-sensitivity photodiode, low-noise amplifier, 16-bit ADC, and supports a simple I2C bus interface with an optional interrupt function.

Key parameter highlights:

• Very high sensitivity: resolution down to 0.0021 lx per count
• Wide dynamic range: 0 lx to approximately 18 klx
• Low-power design: shutdown mode current about 1 μA
• Operating temperature range: -25°C to +85°C
• Flicker suppression: support for 100 Hz and 120 Hz flicker noise rejection

2. System Architecture and Operation

2.1 Functional Block Description

The VEML3235 contains a temperature-compensated ALS photodiode, low-pass filter, output buffer, and I2C interface among other key blocks. Pin definitions are as follows:

• Pin 1: GND (ground)
• Pin 2: SDA (I2C data line)
• Pin 3, 4: NC (no connection)
• Pin 5: SCL (I2C clock line)
• Pin 6: VDD (power)

2.2 Application Circuit Design

Power configuration:

• Main supply: 2.6 V to 3.6 V
• I2C pull-up supply: 1.7 V to 3.6 V (can be level-matched to the microcontroller)

External component recommendations:

• Pull-up resistors R1, R2: recommended 2.2 kΩ to 4.7 kΩ
• Decoupling capacitors C1, C2: 10 μF and 100 nF
• Series resistor R4: 10 Ω (use if supply noise is significant)

3. Register Configuration Details

3.1 Register Map

The VEML3235 contains six user-accessible 16-bit command registers at addresses 0x00 to 0x06 (0x03 reserved).

Key register functions:

Command register 0x00 configuration:

• SD bit (bit 0): set to 1 to turn off BG and LDO (default)
• SD0 bit (bit 7): set to 1 to disable ALS and white light channel (default)
• DG bit (bit 5): digital gain selection (0 = ×1, 1 = ×2)
• GAIN bits (bits 4:3): analog gain selection
  • 00 = ×1, 01 = ×2, 11 = ×4

Integration time setting (bits 6:4):

• 000 = 50 ms
• 001 = 100 ms (standard)
• 010 = 200 ms
• 011 = 400 ms
• 100 = 800 ms

4. Applications and Performance Benefits

4.1 Dark Glass Cover Applications

In applications with low-transmittance dark cover glass, the VEML3235 sensitivity of 0.0021 lx ensures accurate measurement even under low-light conditions.

4.2 Light Source Type Identification

By comparing the ratio of the ALS channel to the white-light channel, different light source types can be distinguished:

• Sources with strong infrared component (halogen/incandescent): ratio > 2
• Other sources (LED/fluorescent): ratio ≤ 2

4.3 Environmental Adaptability

The sensor shows good matching across various light sources, including LED, fluorescent, daylight, and halogen, with typical error around ±10%.

5. Typical Illuminance Reference

6. Design Considerations

1. Startup timing: wait 4 ms after enabling the sensor before taking the first measurement
2. Saturation avoidance: when light conditions are unknown, begin measurements at the lowest gain
3. Supply noise: use R-C decoupling if supply line noise is significant
4. Window design: ensure the cover window is fully transparent over the visible range (400 nm to 700 nm)