TSL237 Light-to-Frequency Converter

The TSL237 light-to-frequency converter combines a silicon photodiode and a current-to-frequency converter on a single monolithic CMOS-integrated circuit. The output is a square wave (50% duty cycle) with frequency directly proportional to light intensity. Because it is TTL-compatible, the output allows direct interface to a microcontroller or other logic circuitry. The device has been temperature-compensated for the ultraviolet-to-visible light range of 320 nm to 700 nm and responds over the light range of 320 nm to 1050 nm (Note that the TSL235R/TSL237R differ only in their output frequency range).
 

Key Features:

• Communicates directly with a microcontroller.
• Single-supply operation.
• Compact 3-lead clear plastic package.
• High-resolution conversion of light intensity to frequency with no external components.
   

Application Ideas:

• Camera exposure.
• Dimming displays.
• Machine vision.
   

Details:

• Nonlinearity Error (Typically 0.2% at 100 kHz).
• Stable 150 ppm/°C Temperature Coefficient.
• Supply Voltage: 2.7 - 5.5 VDC.
• Operating Temperature range: -25 - 70 °C.
• Typical current draw: 2 mA.
• Output Frequency: 40 - 60 kHz.
   

NOTES: Power-supply lines must be decoupled by a 0.01 µF to 0.1 µF capacitor with short leads placed close to the TSL235R. The output of the device is designed to drive a standard TTL or CMOS logic input over short distances. If lines greater than 12 inches are used on the output, a buffer or line driver is recommended.