TSL220
TSL220 Light-to-Frequency Converter
Overview
The TSL220 is an integrated optoelectronic device combining a large-area photodiode with a precision current-to-frequency converter. This monolithic solution converts light intensity (irradiance) into a proportional digital frequency output, making it ideal for light measurement applications requiring high sensitivity and wide dynamic range.
The device outputs a CMOS-compatible pulse train whose frequency varies linearly with incident light intensity. The output frequency range can be adjusted using an external capacitor, providing design flexibility. The TSL220 operates over a temperature range of -25°C to 70°C and is packaged in an 8-pin DIP (Dual In-line Package) with a clear plastic window for light access.
Key Features
- Integrated photodiode and current-to-frequency converter
- CMOS-compatible pulse train output
- Linear frequency response to light intensity
- Wide dynamic range operation
- Adjustable output frequency via external capacitor
- High sensitivity to low light levels
- Excellent noise immunity
- Operating temperature range: -25°C to +70°C
- 8-pin clear plastic DIP package
- Active photodiode area: 4.13 mm² (0.0064 in²)
Applications
The TSL220 is suitable for a wide range of light sensing applications including:
- Light intensity measurement
- Lux meters and ambient light sensors
- Optical encoders
- Color measurement systems
- Industrial light monitoring
- Automated lighting control systems
- Photographic exposure control
- Medical instrumentation
- Laboratory equipment
Electrical Characteristics
(TA = 25°C unless otherwise noted)
- Supply Voltage (VCC): 4.5V to 5.5V
- Supply Current: 2.5mA typical
- Output Frequency Range: Adjustable via external capacitor (C1 and C2)
- Output Logic Levels: CMOS compatible (0V to VCC)
- Frequency Linearity Error: ±0.2% typical
- Dark Frequency: 10Hz typical (with C1 = C2 = 220pF)
- Photodiode Responsivity: 45µA/µW/cm² typical at 640nm
- Output Rise/Fall Time: 100ns typical
Package Information
The TSL220 is available in an 8-pin plastic dual in-line package (DIP) with the following mechanical specifications:
- Package Type: 8-pin DIP
- Package Material: Clear plastic
- Overall Dimensions: 9.5mm (0.374") max length × 6.5mm (0.256") max width
- Pin Spacing: 2.54mm (0.100") between pins
- Lead Length: 3.2mm (0.126") minimum
- Photodiode Active Area: 4.13mm² (0.0064 in²)
Pin Configuration
| Pin Number | Pin Name | Description |
|---|---|---|
| 1 | NC | No connection (leave unconnected) |
| 2 | OUTPUT | CMOS-compatible frequency output |
| 3 | VCC | Positive supply voltage (4.5V to 5.5V) |
| 4 | C2 | External capacitor connection (frequency adjustment) |
| 5 | GND | Ground reference |
| 6 | C1 | External capacitor connection (frequency adjustment) |
| 7 | NU | Not usable (leave unconnected) |
| 8 | NU | Not usable (leave unconnected) |
Functional Description
The TSL220 operates by converting photocurrent generated in the integrated photodiode into a proportional frequency output. The conversion process involves:
- Light incident on the photodiode generates a photocurrent proportional to the light intensity
- The current-to-frequency converter processes this photocurrent
- An external capacitor (connected between C1 and C2 pins) sets the output frequency range
- The circuit produces a square wave output whose frequency is linearly proportional to the light intensity
The output frequency can be measured using various techniques including pulse counting, period timing, or integration methods. For LSTTL logic families, a 3300Ω pulldown resistor may be required on the output pin.
Design Considerations
When designing with the TSL220, consider the following:
- Select appropriate capacitor values for C1 and C2 based on desired frequency range
- Ensure proper power supply decoupling near the device
- For best accuracy, maintain stable operating temperature
- Minimize stray capacitance on the C1 and C2 pins
- When measuring low light levels, consider shielding from ambient light interference
- For LSTTL compatibility, add a 3300Ω pulldown resistor on the output
Performance Characteristics
The TSL220 exhibits excellent performance characteristics including:
- High linearity across its operating range
- Low dark current (resulting in low dark frequency)
- Wide dynamic range (typically 6 decades of light intensity)
- Stable operation over temperature
- Fast response to light intensity changes
