LTR-4206E Phototransistor Data Sheet - T-1 Package - 30V Collector-Emitter Voltage - Black Lens - English Technical Documentation

1. Product Overview

The LTR-4206E series is a phototransistor housed in a standard T-1 (3mm) package. This component is specifically engineered for infrared detection applications. Its defining feature is a special dark dye integrated into the lens, which effectively blocks ambient visible light. This design makes it an optimal partner for pairing with infrared emitters in various optoelectronic systems, enhancing signal integrity by minimizing interference from environmental light sources.

1.1 Key Features and Advantages

The device offers several advantages for designers. It is a lead-free product and complies with RoHS environmental directives. It exhibits high radiant sensitivity in the infrared spectrum. The integrated daylight filter function, achieved through the black lens material, is crucial for stable operation in varying lighting conditions. Its core advantage lies in its ability to provide reliable detection of infrared signals while rejecting unwanted visible light noise.

1.2 Target Applications and Market

The LTR-4206E is designed for a range of position-sensing and interruption applications. Primary use cases include position sensors, opto-interrupters (slotted optical switches), encoders for rotational or linear motion detection, and general-purpose optical switches. These applications are common in office automation equipment, industrial controls, consumer electronics, and safety devices where non-contact sensing is required.

2. Technical Parameters: In-Depth Objective Interpretation

This section provides a detailed analysis of the electrical and optical parameters specified in the datasheet, explaining their significance for circuit design.

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. The maximum power dissipation is 100 mW, which dictates the thermal design limits. The Collector-Emitter voltage (Vce) can withstand up to 30V, while the reverse Emitter-Collector voltage (Vec) is limited to 5V, indicating the phototransistor's asymmetry and the importance of correct polarity. The operating temperature range is from -40°C to +85°C, suitable for industrial and consumer environments. The lead soldering temperature is specified as 260°C for a maximum of 5 seconds at a point 1.6mm from the body, providing clear guidelines for assembly processes.

2.2 Electrical and Optical Characteristics

The characteristics are defined at a standard ambient temperature (Ta) of 25°C. Key parameters include the Collector Dark Current (I_CEO), with a maximum of 100 nA at Vce=10V and no illumination. This low dark current is essential for achieving a good signal-to-noise ratio. The On-State Collector Current (I_CON) is a critical parameter measured at Vce=5V with an irradiance (Ee) of 1 mW/cm² from a 940nm source. This current varies significantly across different \"Bin\" grades, which is a core part of the device's grading system. The Rise and Fall Times (t_r, t_f) are typically 10 µs each under specified test conditions (Vcc=5V, Ic=1mA, R_L=1kΩ), defining the device's switching speed. The Angle of Half Sensitivity (θ½) is ±20 degrees, describing the angular reception profile. The spectral response peaks at a wavelength (λ_{S MAX}) of 900 nm and has a bandwidth (λ) ranging from 800 nm to 1100 nm, confirming its optimization for the near-infrared region.

3. Binning System Explanation

The LTR-4206E utilizes a binning system primarily for the On-State Collector Current (I_CON). This system categorizes devices based on their measured sensitivity under standardized test conditions. The datasheet lists bins labeled B through F. For example, Bin B devices have an I_CON range of 0.4 mA (min) to 1.2 mA (max), while Bin F devices range from 6.4 mA (min) upwards. This binning allows manufacturers and designers to select components with consistent performance levels for their specific application requirements, ensuring circuit stability and predictable behavior. Designers must consult the specific bin code when selecting or specifying the part for production.

4. Performance Curve Analysis

The datasheet includes several typical characteristic curves that provide insight into device behavior under non-standard conditions.

4.1 Collector Dark Current vs. Ambient Temperature

Figure 1 shows that the Collector Dark Current (I_CEO) increases exponentially with rising ambient temperature. This is a fundamental semiconductor behavior. Designers must account for this increased leakage current in high-temperature applications, as it can affect the \"off\" state signal level and noise floor.

4.2 Relative Collector Current vs. Irradiance

Figure 4 illustrates the relationship between the output collector current and the incident infrared irradiance. The curve is generally linear over a significant range, which is desirable for analog sensing applications. Understanding this transfer function is key to calibrating the sensor for specific light intensity measurements.

4.3 Relative Radiant Sensitivity vs. Wavelength

Figure 5 depicts the spectral sensitivity curve. It clearly shows peak sensitivity around 900 nm and a defined roll-off at both shorter (visible) and longer (infrared) wavelengths. The black lens material contributes to attenuating the response in the visible spectrum, as seen in the curve. This graph is vital for ensuring compatibility between the detector and the wavelength of the chosen infrared emitter (typically 850nm, 880nm, or 940nm).

4.4 Angular Displacement Characteristics

Figure 6 shows the relative sensitivity as a function of angular displacement from the optical axis. The sensitivity pattern is roughly cosine-like, with the half-sensitivity point at ±20 degrees. This information is crucial for mechanical alignment in designs like slotted opto-interrupters or reflective sensors, defining the tolerance for misalignment.

5. Mechanical and Package Information

5.1 Outline Dimensions

The device uses a standard T-1 (3mm diameter) package. Key dimensions include the body diameter, lead spacing, and overall length. The lead spacing is measured where the leads emerge from the package. A note specifies that the maximum protrusion of resin under the flange is 1.5mm, which is important for PCB layout and clearance.

5.2 Recommended Solder Pad and Polarity Identification

Figure 7 provides a recommended solder pad footprint for PCB design. The pad layout is asymmetrical, with one pad designated for the cathode and the other for the anode. The cathode is typically identified by a longer lead or a flat spot on the package body. Following this footprint ensures proper soldering and mechanical stability. The recommended copper area and solder resist pattern are specified to achieve reliable solder joints.

6. Soldering and Assembly Guidelines

Proper handling is critical for reliability. Leads should be formed at a point at least 3mm from the base of the lens, and the base should not be used as a fulcrum. Forming must be done before soldering at normal temperature. During PCB assembly, minimal clinch force should be used. For soldering, dipping the lens into solder must be avoided, and no external stress should be applied to the leads while the device is hot. The recommended solder pad design (see section 5.2) should be followed. For cleaning, only alcohol-based solvents like isopropyl alcohol are recommended.

7. Storage and Handling Cautions

Devices should be stored in an environment not exceeding 30°C and 70% relative humidity. If removed from their original moisture-barrier packaging, they should be used within three months. For longer storage outside the original packaging, a sealed container with desiccant or a nitrogen ambient is recommended. The most critical handling concern is Electrostatic Discharge (ESD). The device is sensitive to ESD. A comprehensive set of ESD prevention measures is provided, including the use of grounded wrist straps, anti-static workstations, ionizers, and proper shielding containers during storage and transport. A detailed checklist for auditing ESD controls is included in the datasheet, covering personnel grounding, workstation setup, and device handling procedures.

8. Application Suggestions and Design Considerations

8.1 Typical Application Circuits

The phototransistor is typically used in a common-emitter configuration. A load resistor (R_L) is connected between the collector and the positive supply (Vcc). The emitter is connected to ground. The output signal is taken from the collector node. The value of R_L affects both the output voltage swing and the switching speed (as shown in Figure 3). A smaller R_L provides faster response but a smaller output voltage change for a given photocurrent. Designers must balance speed and gain based on their specific needs.

8.2 Pairing with an Infrared Emitter

For optimal performance, the LTR-4206E should be paired with an infrared LED whose peak emission wavelength falls within the detector's sensitive range (800-1100 nm, peaking at 900 nm). Common choices are 850nm, 880nm, or 940nm emitters. The drive current for the emitter and the alignment between the emitter and detector are critical factors determining the system's sensing distance and reliability.

8.3 Minimizing Ambient Light Interference

While the black lens provides significant rejection of visible light, it is not perfect. For applications in environments with strong or varying ambient light (e.g., sunlight, fluorescent lamps), additional measures may be necessary. These can include optical shielding (barriers), modulating the infrared emitter signal and using synchronous detection in the receiver circuit, or using electrical filtering to reject signals at the mains frequency (50/60 Hz) typical of artificial lighting.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the black lens?

A: The black lens contains a dye that acts as a visible light filter. It attenuates ambient light in the visible spectrum, allowing the phototransistor to respond primarily to infrared light, thereby improving the signal-to-noise ratio in environments with background illumination.

Q: How do I choose the correct Bin for my application?

A: The Bin selection depends on the required sensitivity. If your circuit requires a higher output current for a given infrared light level (e.g., for longer sensing distances or with weaker emitters), choose a higher Bin (e.g., D, E, F). For applications requiring consistency across many units, specify a tighter Bin range. Consult the I_CON table in section 2.2.

Q: Can I use this for sensing visible light?

A: No. The device's spectral response and the black lens are specifically designed to block visible light. Its sensitivity is minimal in the visible range. For visible light detection, a phototransistor with a clear or diffused lens and a different spectral response should be selected.

Q: What is the significance of the 10 µs rise/fall time?

A: This specifies the device's switching speed. It can be used in applications requiring modulation frequencies up to approximately tens of kilohertz. For very high-speed communication (MHz range), a photodiode or a faster phototransistor would be more appropriate.

10. Operational Principle

A phototransistor is a bipolar junction transistor where the base region is exposed to light. Incident photons with sufficient energy (corresponding to the infrared wavelength in this case) generate electron-hole pairs in the base-collector junction. These photogenerated carriers act as a base current, which is then amplified by the transistor's current gain (beta, β). This results in a collector current that is much larger than the primary photocurrent. The LTR-4206E operates in photoconductive mode, where the applied Vce bias sweeps the carriers across the junction, contributing to its sensitivity and speed.