LTR-C950-TB Infrared Phototransistor Datasheet - Top View Black Lens - 940nm - English Technical Document

1. Product Overview

This document details the specifications for a discrete infrared phototransistor component. The device is designed for sensing infrared light, typically at a wavelength of 940nm. It features a top view package with a black dome lens, which helps in defining the viewing angle and potentially reducing interference from ambient visible light. The component is packaged on tape and reel, making it compatible with high-volume, automated surface-mount assembly processes. It is compliant with relevant environmental standards.

1.1 Features

• Compliant with environmental regulations for hazardous substances.
• Top view form factor with a black dome lens.
• Supplied in 12mm tape on 7-inch diameter reels for automated placement.
• Compatible with standard infrared reflow soldering processes.
• Standardized package outline.

1.2 Applications

• Infrared receiver modules.
• PCB-mounted infrared sensing applications.

2. Outline Dimensions

The device conforms to a standard package outline. All critical dimensions are provided in the datasheet diagrams in millimeters, with a standard tolerance of ±0.1mm unless otherwise specified. The package is designed for reliable PCB mounting.

3. Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. All values are specified at an ambient temperature (TA) of 25°C.

• Power Dissipation (PD): 100 mW
• Collector-Emitter Voltage (VCEO): 30 V
• Emitter-Collector Voltage (VECO): 5 V
• Operating Temperature Range: -40°C to +85°C
• Storage Temperature Range: -55°C to +100°C
• Infrared Reflow Soldering: Peak temperature of 260°C for a maximum of 10 seconds.

A suggested reflow temperature profile for lead-free processes is included, emphasizing pre-heat, peak temperature, and time-above-liquidus parameters to ensure reliable solder joints without thermal damage.

4. Electrical & Optical Characteristics

These parameters define the device's performance under specified test conditions at TA=25°C. They are crucial for circuit design.

• Collector-Emitter Breakdown Voltage, V(BR)CEO: 30 V (min). Test condition: IR = 100µA, Irradiance (Ee) = 0 mW/cm².
• Emitter-Collector Breakdown Voltage, V(BR)ECO: 5 V (min). Test condition: IE = 100µA, Ee = 0 mW/cm².
• Collector-Emitter Saturation Voltage, VCE(SAT): 0.4 V (max). Test condition: IC = 100µA, Ee = 0.5 mW/cm².
• Rise Time (Tr) & Fall Time (Tf): 15 µs (typical). Test condition: VCE = 5V, IC = 1mA, RL = 1kΩ.
• Collector Dark Current (ICEO): 100 nA (max). Test condition: VCE = 20V, Ee = 0 mW/cm². This is the leakage current when no light is incident.
• On-State Collector Current, IC(ON): Ranges from 1.5 mA (min) to 9.20 mA (max). Test condition: VCE = 5V, Ee = 0.5 mW/cm², λ=940nm. This is the key parameter indicating sensitivity.

5. Bin Code System

The devices are sorted into performance bins based on their On-State Collector Current (IC(ON)) to ensure consistency in application. The tolerance for current within each bin is ±15%.

• BIN A: IC(ON) = 1.5 mA to 2.9 mA
• BIN B: IC(ON) = 2.9 mA to 5.5 mA
• BIN C: IC(ON) = 5.5 mA to 9.2 mA

6. Typical Performance Curves

The datasheet provides several graphs illustrating device behavior under various conditions. These are essential for understanding performance beyond the single-point specifications.

• Spectral Sensitivity: A curve showing the relative sensitivity of the phototransistor across different wavelengths, peaking around 940nm.
• Collector Dark Current vs. Ambient Temperature: Shows how leakage current (ICEO) increases with rising temperature.
• Rise and Fall Time vs. Load Resistance: Illustrates how switching speed is affected by the value of the load resistor (RL) in the circuit.
• Relative Collector Current vs. Irradiance: Demonstrates the relationship between incident light power (Ee) and the output collector current.
• Sensitivity Diagram: A polar plot showing the relative angular response of the sensor, which is influenced by the black dome lens.

7. Soldering Pad Layout & Package Information

Recommended PCB land pattern (solder pad) dimensions are provided to ensure proper soldering and mechanical stability. A stencil thickness of 0.1mm or 0.12mm is suggested for solder paste application. Detailed dimensions for the tape and reel packaging are also included, specifying pocket spacing, reel diameter, and hub size to facilitate automated handling.

8. Handling, Storage & Assembly Guidelines

8.1 Storage Conditions

For unopened, moisture-proof bags with desiccant, store at ≤ 30°C and ≤ 90% RH, with a recommended use-within period of one year. For devices removed from their original packaging, the ambient should not exceed 30°C / 60% RH. If stored outside the original bag for more than one week, a bake-out at 60°C for 20 hours is recommended prior to soldering to remove moisture and prevent "popcorning" during reflow.

8.2 Cleaning

If cleaning is necessary, use alcohol-based solvents like isopropyl alcohol.

8.3 Soldering Recommendations

Detailed parameters for both reflow and hand soldering are provided:

• Reflow Soldering: Pre-heat to 150-200°C for up to 120 seconds, with a peak temperature not exceeding 260°C for a maximum of 10 seconds. Reflow should be performed a maximum of two times.
• Hand Soldering: Iron tip temperature should not exceed 300°C, with a soldering time of 3 seconds maximum per joint.

The guidelines reference JEDEC standards and emphasize the need to characterize the process for specific PCB designs.

8.4 Drive Circuit Considerations

The phototransistor is a current-output device. For applications involving multiple sensors, it is strongly recommended to use individual current-limiting resistors in series with each device (as shown in the datasheet's "Circuit A") to ensure uniform response and prevent current hogging by any single unit. Connecting devices directly in parallel ("Circuit B") without individual resistors can lead to mismatched performance due to variations in device characteristics.

9. Application Notes & Design Considerations

9.1 Principle of Operation

An infrared phototransistor operates by converting incident infrared light into an electrical current. Photons with sufficient energy (corresponding to the device's sensitive wavelength, around 940nm) are absorbed in the base region of the transistor, generating electron-hole pairs. This photogenerated current acts as a base current, which is then amplified by the transistor's gain, resulting in a larger collector current that is proportional to the incident light intensity. The black dome lens helps to focus incoming light and defines the field of view.

9.2 Typical Application Scenarios

The primary use is in infrared reception systems. This includes:

• Remote Control Receivers: Decoding signals from TV, audio, and appliance remotes.
• Proximity Sensing: Detecting the presence or absence of an object by reflecting an IR beam.
• Basic Optical Switching: Interrupting a beam for counting or position detection.
• Simple Data Links: Low-speed, short-range wireless data transmission using modulated IR light.

9.3 Design Checklist

• Select the appropriate Bin Code based on the required sensitivity for your application.
• Choose a load resistor (RL) considering the desired output voltage swing and the trade-off with response speed (see Rise/Fall Time vs. RL curve).
• Implement proper filtering in the signal conditioning circuit to reject noise from ambient light (e.g., fluorescent lamp flicker at 100/120Hz).
• Follow the recommended PCB layout and soldering guidelines to ensure reliability.
• Consider the angular sensitivity diagram when designing the mechanical placement and housing to ensure the sensor is aimed correctly.

9.4 Performance vs. Temperature

Designers must account for temperature effects. The Collector Dark Current (ICEO) increases significantly with temperature, which can raise the noise floor in low-light applications. The photocurrent itself also has a temperature coefficient. For critical applications over a wide temperature range (-40°C to +85°C), testing or simulation across the temperature extremes is advised.

10. Technical Comparison & Selection Guidance

When selecting an infrared photodetector, key differentiators include:

• Phototransistor vs. Photodiode: Phototransistors provide internal gain, yielding a larger output signal for a given light level, simplifying subsequent amplifier design. However, they are generally slower in response time than photodiodes. This device, with 15µs rise/fall time, is suitable for standard remote control signals (e.g., 38kHz carrier) but may be too slow for very high-speed data communication.
• Wavelength: The 940nm peak sensitivity is ideal for pairing with common GaAs infrared emitters and is less visible to the human eye compared to 850nm sources, reducing perceived light pollution.
• Package and Lens: The top-view black lens package is optimized for surface-mount assembly and provides a controlled viewing angle, which can help reject stray light from the sides.

11. Frequently Asked Questions (FAQ)

Q: What is the purpose of the Bin Code?
A: The Bin Code ensures a predictable range of sensitivity (IC(ON)). For consistent performance in production, specify the required bin when ordering.

Q: Can I use this sensor in sunlight?
A: Direct sunlight contains a massive amount of infrared radiation and will likely saturate the sensor. It is designed for indoor use or controlled environments. Optical filtering or pulsed operation with synchronous detection may be necessary for outdoor use.

Q: Why is the storage and baking procedure so important?
A: Surface-mount packages can absorb moisture from the air. During the high-temperature reflow soldering process, this moisture can vaporize rapidly, causing internal delamination or cracks ("popcorning"), which destroys the component. Proper storage and baking prevent this.

Q: How do I calculate the output voltage?
A: The phototransistor acts as a current source. The output voltage at the collector is approximately VCC - (IC * RL). Choose RL and VCC based on the desired output swing and the expected IC from the light source.

12. Practical Design Example

Scenario: Designing a simple IR receiver for a 38kHz modulated remote control signal.

1. Component Selection: Use this phototransistor (e.g., BIN B for medium sensitivity) and pair it with a 38kHz bandpass filter or a dedicated decoder IC.
2. Bias Circuit: Connect the collector to a 5V supply (VCC) through a load resistor RL. The emitter connects to ground. A value of RL = 1kΩ is a common starting point, providing a good balance between output voltage swing and speed.
3. Signal Conditioning: The voltage at the collector will drop when IR light is detected. This AC-coupled signal is then fed into an amplifier or comparator stage to clean up the digital waveform. A capacitor in parallel with RL can help filter high-frequency noise but will slow the response.
4. Layout: Place the sensor at the front of the PCB with a clear aperture in the enclosure. Keep it away from noise sources like switching regulators. Follow the recommended solder pad layout.

13. Technology Trends

The field of discrete infrared components continues to evolve. Trends include the development of photodetectors with integrated signal conditioning ICs in a single package, providing digital output and enhanced ambient light rejection. There is also a push for higher-speed devices to enable faster data transmission for applications like IR data association (IrDA) and gesture sensing. Furthermore, improvements in packaging aim to provide narrower and more consistent viewing angles for precise sensing applications while maintaining compatibility with automated assembly processes. The device described in this datasheet represents a mature, reliable solution for cost-sensitive, high-volume applications where basic infrared detection is required.