LTR-209 Phototransistor Datasheet - Clear Package - Vce 30V - Power 100mW - English Technical Document

1. Product Overview

The LTR-209 is a silicon NPN phototransistor designed for infrared detection applications. It is housed in a clear, transparent plastic package which allows for high sensitivity to incident light, particularly in the infrared spectrum. The device is characterized by its wide operating range, reliability, and cost-effectiveness, making it suitable for various sensing and detection systems.

1.1 Core Advantages

• Wide Range of Collector Current: The device supports a broad spectrum of collector current levels, providing flexibility in circuit design and sensitivity adjustment.
• High Sensitivity Lens: The integrated lens enhances the device's sensitivity to incoming infrared radiation, improving signal-to-noise ratio.
• Low-Cost Plastic Package: Utilizes an economical plastic encapsulation, reducing overall system cost.
• Clear Transparent Package: The transparent housing maximizes the amount of light reaching the active semiconductor area, optimizing performance.

2. In-Depth Technical Parameter Analysis

The following section provides a detailed, objective interpretation of the key electrical and optical parameters specified for the LTR-209 phototransistor.

2.1 Absolute Maximum Ratings

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

• Power Dissipation (P_D): 100 mW. This is the maximum power the device can dissipate as heat at an ambient temperature (T_A) of 25°C. Exceeding this limit risks thermal runaway and failure.
• Collector-Emitter Voltage (V_CEO): 30 V. The maximum voltage that can be applied between the collector and emitter terminals with the base open (photocurrent only).
• Emitter-Collector Voltage (V_ECO): 5 V. The maximum reverse voltage applicable between emitter and collector.
• Operating Temperature Range: -40°C to +85°C. The ambient temperature range over which the device is designed to function correctly.
• Storage Temperature Range: -55°C to +100°C. The temperature range for non-operational storage without degradation.
• Lead Soldering Temperature: 260°C for 5 seconds at 1.6mm from the package body. This defines the acceptable thermal profile for hand or wave soldering processes.

2.2 Electrical & Optical Characteristics

These parameters are measured under specific test conditions at T_A=25°C and define the typical performance of the device.

• Collector-Emitter Breakdown Voltage (V_(BR)CEO): 30 V (Min). Measured at I_C = 1mA with zero irradiance (E_e = 0 mW/cm²). This confirms the absolute maximum rating.
• Emitter-Collector Breakdown Voltage (V_(BR)ECO): 5 V (Min). Measured at I_E = 100µA with zero irradiance.
• Collector-Emitter Saturation Voltage (V_CE(SAT)): 0.4 V (Max). The voltage drop across the device when it is fully "on" (conducting), measured at I_C = 100µA and E_e = 1 mW/cm². A lower V_CE(SAT) is desirable for lower power loss.
• Rise Time (T_r) & Fall Time (T_f): 10 µs (Typ) and 15 µs (Typ) respectively. These parameters define the switching speed of the phototransistor. Measured under conditions of V_CC=5V, I_C=1mA, and R_L=1kΩ. The asymmetry is common in phototransistors.
• Collector Dark Current (I_CEO): 100 nA (Max). This is the leakage current that flows from collector to emitter when the device is in complete darkness (E_e = 0 mW/cm²) and V_CE = 10V. A low dark current is critical for high-sensitivity applications to minimize noise.

3. Binning System Explanation

The LTR-209 employs a binning system for its key parameter, On-State Collector Current (I_C(ON)). Binning is a quality control process where components are sorted based on measured performance into specific groups or "bins." This allows designers to select a device with a guaranteed performance range suitable for their application.

3.1 On-State Collector Current Binning

The I_C(ON) is measured under standardized conditions: V_CE = 5V, E_e = 1 mW/cm², and an infrared source wavelength (λ) of 940nm. The device is sorted into the following bins based on its measured current:

• BIN C: 0.8 mA (Min) to 2.4 mA (Max)
• BIN D: 1.6 mA (Min) to 4.8 mA (Max)
• BIN E: 3.2 mA (Min) to 9.6 mA (Max)
• BIN F: 6.4 mA (Min) - No upper limit specified in this datasheet excerpt.

Design Implication: A circuit designed for BIN C devices (lower current) may not function correctly if a BIN F device (higher current) is used without recalibration, and vice-versa. Specifying the bin code is crucial for consistent system performance.

4. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate how key parameters vary with operating conditions. These are essential for understanding real-world behavior beyond the single-point specifications.

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

This graph shows that I_CEO (dark current) increases exponentially with rising ambient temperature (T_A). For instance, at 100°C, the dark current can be orders of magnitude higher than at 25°C. This is a fundamental semiconductor behavior due to increased thermal generation of charge carriers. Design Consideration: In high-temperature applications, the increased dark current can become a significant source of noise, potentially masking weak optical signals. Thermal management or signal conditioning may be necessary.

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

This derating curve shows the maximum allowable power dissipation (P_C) as a function of T_A. The absolute maximum rating of 100 mW is only valid at or below 25°C. As T_A increases, the device's ability to dissipate heat decreases, so the maximum allowed power must be reduced linearly. At 85°C (the maximum operating temperature), the allowable power dissipation is significantly lower. Design Consideration: Circuits must be designed to ensure the actual power dissipated (V_CE * I_C) does not exceed the derated value at the highest expected operating temperature.

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

This curve demonstrates the trade-off between switching speed and signal amplitude. Rise time (T_r) and fall time (T_f) both increase with larger load resistance (R_L). A larger R_L provides a larger output voltage swing (ΔV = I_C * R_L) but slows down the circuit's response time because the transistor's junction capacitance takes longer to charge/discharge through the larger resistor. Design Consideration: The value of R_L must be chosen based on whether the application prioritizes high-speed response (lower R_L) or high output voltage gain (higher R_L).

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

This graph plots the normalized collector current against the incident optical power density (irradiance, E_e). It shows a linear relationship in the plotted range (0 to ~5 mW/cm²). This linearity is a key feature of phototransistors used in analog sensing applications, as the output current is directly proportional to the input light intensity. The curve is shown for V_CE = 5V.

4.5 Sensitivity Diagram (Fig. 5)

While the exact axes are abbreviated, a "Sensitivity Diagram" typically illustrates the spectral response of the detector. Silicon phototransistors like the LTR-209 are most sensitive to light in the near-infrared region, peaking around 800-950 nm. This makes them ideal for use with common infrared emitters (like LEDs with λ=940nm, as referenced in the binning test condition) and for filtering out visible light interference.

5. Mechanical & Packaging Information

5.1 Package Dimensions

The device uses a standard through-hole plastic package. Key dimensional notes from the datasheet include:

• All dimensions are in millimeters (inches provided in parenthesis).
• A standard tolerance of ±0.25mm (±.010") applies unless otherwise specified.
• The maximum protrusion of resin under the flange is 1.5mm (.059").
• Lead spacing is measured at the point where the leads exit the package body, which is critical for PCB footprint design.

Polarity Identification: The longer lead is typically the collector, and the shorter lead is the emitter. The flat side on the package rim may also indicate the emitter side. Always verify with the package diagram.

6. Soldering & Assembly Guidelines

The primary guidance provided is for hand or wave soldering: the leads can be subjected to a temperature of 260°C for a maximum duration of 5 seconds, measured at a distance of 1.6mm (.063") from the package body. This prevents thermal damage to the internal semiconductor die and the plastic package.

For Reflow Soldering: Although not explicitly stated in this datasheet, similar plastic packages typically require a profile compliant with JEDEC standards (e.g., J-STD-020), with a peak temperature usually not exceeding 260°C. The specific moisture sensitivity level (MSL) and baking requirements are not provided here and should be confirmed with the manufacturer.

Storage Conditions: The device should be stored within the specified temperature range of -55°C to +100°C in a dry, non-corrosive environment. For long-term storage, anti-static precautions are recommended.

7. Application Suggestions

7.1 Typical Application Scenarios

• Object Detection & Proximity Sensing: Used in conjunction with an IR LED to detect the presence, absence, or proximity of an object (e.g., in vending machines, printers, industrial automation).
• Slot Sensors & Encoders: Detecting interruptions in an IR beam to count objects or measure rotational speed.
• Remote Control Receivers: While slower than dedicated photodiodes, they can be used in simple, low-cost IR receiver circuits.
• Light Barriers & Security Systems: Creating an invisible beam for intrusion detection.

7.2 Design Considerations & Circuit Configuration

The most common circuit configuration is the common-emitter mode. The phototransistor is connected with the collector to a positive supply (V_CC) via a load resistor (R_L), and the emitter is connected to ground. Incident light causes a photocurrent (I_C) to flow, generating an output voltage (V_OUT) at the collector node: V_OUT = V_CC - (I_C * R_L). When dark, V_OUT is high (~V_CC). When illuminated, V_OUT drops.

Key Design Steps:

1. Select R_L: Based on required output swing (V_CC/I_C(ON)) and desired speed (see Fig. 3). Values between 1kΩ and 10kΩ are common.
2. Consider Bandwidth: The R_L value, combined with the device's junction capacitance, forms a low-pass filter. For pulsed operation, ensure the circuit's RC time constant is much shorter than the pulse width.
3. Manage Ambient Light: Use optical filtering (a dark or IR-pass filter over the sensor) to block unwanted visible light and reduce noise.
4. Temperature Compensation: For precision analog sensing, consider the temperature dependence of dark current (Fig. 1). Techniques include using a matched dark reference sensor in a differential configuration or implementing software compensation.

8. Technical Comparison & Differentiation

Compared to other optical detectors:

• vs. Photodiode: A phototransistor provides inherent current gain (β or h_FE), resulting in a much higher output current for the same light level. This simplifies circuit design as less subsequent amplification is needed. However, phototransistors are generally slower (longer rise/fall times) and have a more limited linear range than photodiodes.
• vs. Photodarlington: A photodarlington offers even higher gain than a standard phototransistor but has significantly slower response times and a higher saturation voltage (V_CE(SAT)). The LTR-209 offers a good balance of gain, speed, and voltage drop.
• Differentiating Feature of LTR-209: Its clear package and integrated lens are key differentiators. Many competing phototransistors use black epoxy packages that attenuate light. The clear package of the LTR-209 maximizes sensitivity, while the lens helps focus incoming light onto the active area, improving directionality and signal strength.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 What does the "BIN" code mean, and why is it important?

The BIN code (C, D, E, F) categorizes the device based on its measured On-State Collector Current (I_C(ON)). It is crucial because it guarantees a specific performance range. Using a device from the wrong bin could cause your circuit to be under-sensitive or over-sensitive, leading to malfunction. Always specify the required bin when ordering.

9.2 Can I use this sensor with a visible light source?

While the silicon material does respond to visible light, its peak sensitivity is in the near-infrared (see implied Fig. 5). For optimal performance and to avoid interference from ambient visible light, it is strongly recommended to pair it with an infrared emitter (typically 850nm, 880nm, or 940nm) and use an IR-pass filter on the detector.

9.3 How do I convert the output to a digital signal?

The simplest method is to connect the output (collector node) to the input of a Schmitt-trigger inverter or a comparator with hysteresis. This converts the analog voltage swing into a clean digital signal, immune to noise. The threshold of the comparator should be set between the "light" and "dark" output voltage levels.

9.4 Why is my output unstable in a bright, hot environment?

This is likely due to the combined effects of high dark current (increasing with temperature per Fig. 1) and response to ambient light. Solutions include: 1) Adding a physical shield or tube to limit the field of view, 2) Using a modulated IR source and synchronous detection, 3) Implementing a temperature-stable biasing or compensation circuit.

10. Practical Design Case Study

Scenario: Designing a paper detection sensor for a printer.

Implementation: An IR LED and the LTR-209 are placed on opposite sides of the paper path, aligned to create a beam. When paper is present, it blocks the beam. The phototransistor is configured in common-emitter mode with R_L = 4.7kΩ and V_CC = 5V.

Component Selection & Calculations: Select a device from BIN D (I_C(ON) = 1.6-4.8mA). With no paper (beam intact), assume I_C = 3mA (typical). V_OUT = 5V - (3mA * 4.7kΩ) = 5V - 14.1V = -9.1V. This is impossible, meaning the transistor is saturated. In saturation, V_OUT ≈ V_CE(SAT) ≈ 0.4V (a LOW signal). When paper blocks the beam, I_C ≈ I_CEO (very small, ~nA), so V_OUT ≈ 5V (a HIGH signal). A microcontroller GPIO pin can read this HIGH/LOW signal directly to detect paper presence. A decoupling capacitor (e.g., 100nF) across the sensor's supply pins is recommended to filter noise.

11. Operating Principle

A phototransistor is a bipolar junction transistor (BJT) where the base region is exposed to light. Incident photons with sufficient energy create electron-hole pairs in the base-collector junction. These photogenerated carriers are swept by the internal electric field, effectively acting as a base current. This "optical base current" is then amplified by the transistor's current gain (h_FE), resulting in a much larger collector current. The magnitude of this collector current is proportional to the intensity of the incident light, providing the sensing function. The clear package and lens of the LTR-209 maximize the number of photons reaching the sensitive semiconductor junction.

12. Technology Trends

Phototransistors like the LTR-209 represent a mature and cost-effective technology. Current trends in optoelectronics include:

• Integration: Moving towards integrated solutions that combine the photodetector, amplifier, and digital logic (e.g., photo-interrupters with built-in logic output) on a single chip, reducing external component count and improving noise immunity.
• Surface-Mount Devices (SMD): While through-hole packages remain popular for prototyping and certain applications, there is a strong industry shift towards smaller SMD packages (e.g., SMT-3) for automated assembly and space-constrained designs.
• Enhanced Performance: Development of devices with faster response times, lower dark currents, and improved temperature stability for more demanding applications in automotive, industrial, and consumer electronics.
• Application-Specific Optimization: Sensors are being tailored for specific wavelengths (e.g., for heart-rate monitoring at specific IR wavelengths) or with built-in daylight filters.

The fundamental operating principle of the phototransistor remains valid, and devices like the LTR-209 continue to be a reliable choice for a vast array of basic to intermediate sensing needs due to their simplicity, robustness, and low cost.