PicoMOSFET Series# Technical Documentation: CPH3438 Phototransistor
*Manufacturer: SANYO*
## 1. Application Scenarios
### Typical Use Cases
The CPH3438 is a high-sensitivity silicon NPN phototransistor designed for optical detection applications. Its primary use cases include:
- Optical Switching Systems : Position detection in industrial automation equipment
- Object Detection : Presence/absence sensing in conveyor systems and assembly lines
- Rotary Encoders : Speed and position monitoring in motor control systems
- Light Barrier Systems : Safety interlocks and access control systems
- Ambient Light Sensing : Automatic brightness control in display systems
### Industry Applications
- Industrial Automation : Machine vision systems, robotic positioning sensors
- Consumer Electronics : Automatic backlight control for displays, proximity sensors
- Automotive : Rain sensors, twilight sensors, position detection
- Medical Equipment : Fluid level detection, equipment positioning
- Security Systems : Intrusion detection, door position monitoring
### Practical Advantages and Limitations
Advantages:
- High photosensitivity with typical collector current of 2.0mA (Ee=1mW/cm², λ=940nm)
- Fast response time (typical ton=15μs, toff=15μs)
- Wide operating temperature range (-25°C to +85°C)
- Compact surface-mount package (3.2×2.7×2.1mm)
- Low dark current (maximum 100nA)
Limitations:
- Limited spectral response range (peak sensitivity at 940nm)
- Susceptible to ambient light interference without proper filtering
- Requires careful PCB layout for optimal performance
- Temperature-dependent characteristics require compensation in precision applications
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Ambient Light Interference
- Problem : False triggering from environmental light sources
- Solution : Implement optical filtering (940nm bandpass) and modulated light sources with synchronous detection
Pitfall 2: Saturation Effects
- Problem : Output saturation under high illumination conditions
- Solution : Use series current-limiting resistors and ensure proper biasing
Pitfall 3: Temperature Drift
- Problem : Performance variation across temperature ranges
- Solution : Implement temperature compensation circuits or use temperature-stable biasing
### Compatibility Issues with Other Components
LED Driver Compatibility:
- Requires matching with 940nm infrared LEDs (recommended: SANYO's compatible LED series)
- Ensure proper current drive capability (typically 20-100mA for paired LEDs)
Microcontroller Interface:
- Compatible with standard 3.3V and 5V logic families
- May require pull-up resistors for open-collector configuration
- ADC interface requires appropriate voltage scaling and filtering
Power Supply Considerations:
- Operating voltage: 5V maximum
- Requires stable power supply with minimal noise for precision applications
### PCB Layout Recommendations
Component Placement:
- Position CPH3438 close to the detecting LED to minimize optical path
- Maintain minimum 2mm clearance from other components
- Avoid placement near heat-generating components
Routing Guidelines:
- Use ground plane for noise reduction
- Keep signal traces short and direct
- Implement proper decoupling (100nF ceramic capacitor near supply pins)
- Separate analog and digital ground planes with single-point connection
Optical Considerations:
- Ensure unobstructed optical path to target
- Consider aperture design for directional sensitivity control
- Use opaque housing to prevent stray light interference
## 3. Technical Specifications
### Key Parameter Explanations
Absolute Maximum Ratings:
- Collector-Emitter Voltage (VCEO): 30V
- Emitter-Collector Voltage (VECO): 5V
- Collector Current (IC):
