LTR-1650D Phototransistor Datasheet - Package Dimensions 5.0x4.0x3.2mm - Voltage 30V - Power 100mW - Dark Transparent Package - English Technical Document

1. Product Overview

The LTR-1650D is a silicon NPN phototransistor designed for infrared detection applications. It is housed in a low-cost, dark transparent plastic package which allows for effective filtering of visible light while transmitting infrared wavelengths, primarily around 940nm. The integrated lens enhances the device's sensitivity by focusing incident infrared radiation onto the active area of the transistor. This component is engineered for reliability and performance across a broad operating temperature range, making it suitable for various sensing and control systems.

2. Key Features and Core Advantages

• Wide Range of Collector Current: The device offers multiple performance bins (A through F) providing a wide selection of on-state collector current (IC(ON)) from 0.2mA minimum to over 9.6mA maximum, allowing designers to select a part matching specific sensitivity requirements.
• High-Sensitivity Lens: The integrated epoxy lens increases the effective collection area for infrared light, improving the signal-to-noise ratio and overall responsivity.
• Cost-Effective Plastic Package: Utilizes a standard, economical plastic housing for mass production and broad market adoption.
• Special Dark Transparent Package: The package material is tinted to attenuate visible light, reducing interference from ambient light sources and enhancing performance in environments with fluctuating light conditions.

3. In-Depth Technical Parameter Analysis

3.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Power Dissipation (P_D): 100 mW at T_A=25°C. This is the maximum power the device can safely dissipate as heat.
• Collector-Emitter Voltage (V_CEO): 30 V. The maximum voltage that can be applied between the collector and emitter terminals with the base open.
• Emitter-Collector Voltage (V_ECO): 5 V. The maximum reverse voltage applicable between emitter and collector.
• Operating Temperature Range (T_opr): -40°C to +85°C. The ambient temperature range over which the device is specified to operate.
• Storage Temperature Range (T_stg): -55°C to +100°C.
• Lead Soldering Temperature: 260°C for 5 seconds at a distance of 1.6mm from the package body. This is critical for wave or reflow soldering processes.

3.2 Electrical & Optical Characteristics (T_A=25°C)

The following parameters are tested under specific conditions and define the device's performance.

• Collector-Emitter Breakdown Voltage (V_(BR)CEO): 30 V (Min). Tested at I_C = 1mA with no irradiance (E_e = 0 mW/cm²).
• Emitter-Collector Breakdown Voltage (V_(BR)ECO): 5 V (Min). Tested at I_E = 100µA with no irradiance.
• Collector-Emitter Saturation Voltage (V_CE(SAT)): 0.4 V (Max). The voltage drop across the transistor when it is fully "on," tested at I_C = 100µA and E_e = 1 mW/cm². A low V_CE(SAT) is desirable for efficient switching.
• Rise Time (T_r) & Fall Time (T_f): 10 µs (Typ). These switching speed parameters are measured with V_CC=5V, I_C=1mA, and R_L=1kΩ. They determine how quickly the phototransistor can respond to changes in light intensity.
• Collector Dark Current (I_CEO): 100 nA (Max). This is the leakage current flowing through the collector when the device is in complete darkness (E_e = 0 mW/cm²) with V_CE = 10V. A low dark current is essential for good signal-to-noise ratio in low-light detection.

3.3 On-State Collector Current (I_C(ON)) Binning System

The LTR-1650D is categorized into different bins based on its sensitivity, defined by the On-State Collector Current measured under standardized conditions (V_CE = 5V, E_e = 1 mW/cm², λ = 940nm). This allows for precise selection based on application gain requirements.

• Bin A: 0.2 - 0.6 mA
• Bin B: 0.4 - 1.2 mA
• Bin C: 0.8 - 2.4 mA
• Bin D: 1.6 - 4.8 mA
• Bin E: 3.2 - 9.6 mA
• Bin F: 6.4 mA (Min)

Designers should consult the specific bin code when ordering to ensure the phototransistor meets the circuit's sensitivity and output current needs.

4. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate how key parameters vary with environmental and electrical conditions.

4.1 Collector Dark Current vs. Ambient Temperature (Fig. 1)

This curve shows that the collector dark current (I_CEO) increases exponentially with rising ambient temperature. This is a fundamental semiconductor behavior where thermally generated charge carriers become more prevalent. In high-temperature applications, this increased leakage current can become a significant source of noise and must be accounted for in the design of the sensing amplifier's threshold.

4.2 Collector Power Dissipation vs. Ambient Temperature (Fig. 2)

The graph depicts the derating of the maximum allowable power dissipation as ambient temperature increases. At 25°C, the device can handle 100mW. As temperature rises, this rating decreases linearly. For reliable operation above 25°C, the actual power dissipated (V_CE * I_C) must be kept below the derated curve. This is crucial for preventing thermal runaway and ensuring long-term reliability.

4.3 Rise and Fall Time vs. Load Resistance (Fig. 3)

This curve demonstrates the trade-off between switching speed and load resistance (R_L). Rise and fall times increase with larger load resistors. This is because a larger R_L creates a larger RC time constant with the phototransistor's junction capacitance. For applications requiring fast pulse detection, a smaller load resistor should be used, albeit at the cost of reduced output voltage swing.

4.4 Relative Collector Current vs. Irradiance (Fig. 4)

This plot shows the relationship between incident infrared irradiance (E_e) and the resulting collector current. The response is generally linear over a certain range, which is ideal for analog light sensing applications. The slope of this line represents the device's responsivity. Understanding this characteristic is key for calibrating the sensor's output to a specific light intensity level.

4.5 Sensitivity Diagram (Fig. 5)

This polar diagram illustrates the angular dependence of the phototransistor's sensitivity. The sensitivity is typically highest when infrared light is incident perpendicular to the lens (0°). It decreases as the angle of incidence increases. This characteristic is vital for designing the optical path in an application, such as ensuring proper alignment in a slot-type interrupter or defining the field of view for a proximity sensor.

5. Mechanical and Package Information

5.1 Package Dimensions

The device uses a standard 3mm (T-1) radial leaded package. Key dimensions include:

• Package body diameter: Approximately 5.0mm.
• Package height: Approximately 3.2mm (excluding leads).
• Lead spacing: Measured where leads emerge from the package, typically 2.54mm (0.1").
• A maximum resin protrusion of 1.5mm under the flange is allowed.

Note: All dimensions are in millimeters with a standard tolerance of ±0.25mm unless otherwise specified. Designers must refer to the detailed mechanical drawing for precise footprint and placement planning.

5.2 Polarity Identification

The phototransistor has two leads: the Collector and the Emitter. The longer lead is typically the Collector. The package may also have a flat side or other marking near the Collector lead. Correct polarity is essential for proper circuit operation and applying the correct bias voltage.

6. Soldering and Assembly Guidelines

• Hand Soldering: Use a temperature-controlled iron. Limit soldering time to prevent excessive heat transfer to the semiconductor die.
• Wave/Reflow Soldering: Adhere strictly to the maximum rating: 260°C for 5 seconds, measured 1.6mm from the package body. Exceeding this can damage the internal wire bonds or the epoxy package.
• Cleaning: Use appropriate solvents that are compatible with the dark transparent epoxy resin. Avoid ultrasonic cleaning unless verified to be safe for the package.
• Storage: Store in a dry, anti-static environment within the specified temperature range of -55°C to +100°C to prevent moisture absorption (which can cause "popcorning" during reflow) and electrostatic discharge damage.

7. Application Suggestions and Design Considerations

7.1 Typical Application Scenarios

• Object Detection & Interruption: Used in slot-type optical switches (e.g., paper detection in printers, end-stop sensing in 3D printers).
• Proximity Sensing: Paired with an infrared LED for non-contact detection of objects.
• Encoders: Detecting patterns on rotating disks for speed or position measurement.
• Industrial Control: Sensing in automated equipment where environmental light immunity is required.
• Consumer Electronics: IR remote control receivers (though often used with dedicated ICs, a phototransistor can form the front end).

7.2 Critical Design Considerations

• Biasing Circuit: The phototransistor can be used in either a switch (common-emitter) or follower (emitter-follower) configuration. The common-emitter configuration provides voltage gain and is common for digital switching. A pull-up resistor (R_L) is required.
• Selecting R_L: The value of the load resistor involves a trade-off. A larger R_L gives a larger output voltage swing for a given photocurrent but slows down the switching speed (see Fig. 3). Choose based on required speed and signal level.
• Ambient Light Rejection: While the dark package helps, strong ambient IR sources (sunlight, incandescent bulbs) can saturate the sensor. Consider using optical filters, modulating the IR source, and using synchronous detection techniques.
• Temperature Compensation: For precision analog sensing, the variation of dark current and sensitivity with temperature (Figs. 1 & 2) must be compensated for in the signal conditioning circuitry.
• Electrical Noise: The high-impedance node at the collector can be susceptible to electromagnetic interference (EMI). Keep traces short, use shielding if necessary, and consider adding a small capacitor (e.g., 10-100pF) across R_L to filter high-frequency noise, mindful of its impact on speed.

8. Technical Comparison and Differentiation

Compared to a basic photodiode, a phototransistor like the LTR-1650D provides internal gain, producing a much larger output current for the same light input, which often eliminates the need for an additional external amplifier in simple switching applications. Compared to a photo-Darlington transistor, it offers faster response times (µs vs. tens/hundreds of µs) but lower gain. The specific binning system for I_C(ON) allows for tighter system design compared to devices with a single, broad specification. The dark transparent package is a key differentiator from clear packages, offering built-in visible light suppression.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 What does the "BIN" specification mean, and how do I choose?

The BIN code (A through F) specifies the guaranteed range of the phototransistor's sensitivity (I_C(ON)). Choose a bin based on the required output current for your specific irradiance level. For higher sensitivity/lower light level applications, select a higher bin letter (e.g., E or F). For cost-sensitive applications where high gain is not critical, a lower bin (A or B) may suffice.

9.2 Why is the dark current important?

Dark current (I_CEO) is the output signal present when no light is incident. It sets the lower limit of detectable light and acts as a noise source. In digital switching applications, the circuit's detection threshold must be set above the maximum expected dark current, especially at high temperatures where it increases significantly.

9.3 How does load resistance affect performance?

Load resistance (R_L) directly affects two key parameters: Output Voltage (V_out = I_C * R_L) and Switching Speed (see Fig. 3). You must select R_L to achieve the necessary voltage swing for your logic levels or ADC input, while also ensuring the rise/fall times are fast enough for your application's data rate or response time.

9.4 Can I use this under bright sunlight?

The dark transparent package provides some rejection, but direct sunlight contains intense infrared radiation that can easily saturate the sensor. For outdoor use, additional measures are mandatory: physical shading (hoods), narrowband optical filters centered at your IR source's wavelength (e.g., 940nm), and preferably, using a modulated IR source with synchronous detection in the receiver circuitry to distinguish the signal from the steady DC component of sunlight.

10. Practical Design and Usage Case Study

Scenario: Designing a Paper Detection Sensor for a Printer.

1. Selection: Choose a mid-sensitivity bin (e.g., Bin C or D) to ensure reliable triggering without being overly sensitive to dust or reflections.
2. Circuit Configuration: Use a common-emitter switch configuration. Pair the LTR-1650D with an infrared LED (e.g., 940nm) placed on the opposite side of the paper path.
3. Component Sizing: Select an R_L value (e.g., 4.7kΩ) that provides a logic-low output (near 0V) when paper is present (blocking light, I_C is low) and a logic-high output (near V_CC) when paper is absent (light present, I_C is high). Verify the voltage levels are compatible with the microcontroller's input pins.
4. Noise Immunity: Add a 10nF capacitor in parallel with R_L to suppress electrical noise from printer motors. The resulting speed (~100µs) is still far faster than the mechanical paper movement.
5. Alignment: Use the sensitivity diagram (Fig. 5) to guide mechanical design. Ensure the IR LED and phototransistor are aligned within the high-sensitivity cone (e.g., ±20°) to maximize signal strength.
6. Testing: Test the sensor under worst-case conditions: high temperature (to check for increased dark current) and with various paper types (some may be more translucent to IR).

11. Operating Principle

A phototransistor is fundamentally a bipolar junction transistor (BJT) where the base current is generated by light instead of being supplied electrically. Incident photons with energy greater than the semiconductor's bandgap are absorbed in the base-collector junction region, creating electron-hole pairs. The electric field in the reverse-biased collector-base junction sweeps these carriers, effectively generating a photocurrent that acts as the base current (I_B). This photogenerated base current is then amplified by the transistor's current gain (h_FE), resulting in a much larger collector current (I_C = h_FE * I_B). This internal amplification is the key advantage over a simple photodiode. The dark transparent package material acts as a long-pass filter, allowing infrared wavelengths (like 940nm) to pass while absorbing shorter visible wavelengths, thus improving the signal-to-noise ratio in environments with visible light.

12. Industry Trends and Developments

The optoelectronics sector continues to evolve. While discrete phototransistors like the LTR-1650D remain vital for cost-sensitive, high-volume, or specific performance applications, broader trends include:

• Integration: Increasing integration of the photodetector with analog front-end amplifiers, analog-to-digital converters (ADCs), and digital logic into single-chip solutions (e.g., ambient light sensors, proximity sensor modules). These offer calibrated digital output, smaller footprint, and simplified design but may come at a higher unit cost.
• Miniaturization: Demand for smaller package sizes (e.g., chip-scale packages) to fit into ever-shrinking consumer electronics.
• Enhanced Performance: Development of devices with lower dark currents, faster response times (into the nanosecond range), and higher sensitivity for more demanding applications like LiDAR and high-speed communication.
• Specialization: Sensors tailored for specific wavelengths (e.g., for heart-rate monitoring, gas sensing) or with built-in spectral filters.

Discrete phototransistors will likely maintain their position in applications where their simplicity, robustness, low cost, and specific performance characteristics (like the dark package of the LTR-1650D) provide an optimal solution.