LTR-5576D Phototransistor Datasheet - Package 3.0x2.8x1.9mm - Vce 30V - Power 100mW - Dark Green Filter - English Technical Document

1. Product Overview

The LTR-5576D is a silicon NPN phototransistor designed for infrared detection applications. Its primary function is to convert incident infrared light into an electrical current at its collector terminal. A key distinguishing feature of this component is its special dark green plastic package. This packaging material is specifically chosen to attenuate or cut visible light wavelengths, thereby enhancing the device's sensitivity and selectivity to infrared radiation. This makes it particularly suitable for applications where discrimination between ambient visible light and the intended infrared signal is crucial.

The core advantages of the LTR-5576D include a wide operating range for the collector current, which provides design flexibility. It offers high sensitivity to infrared light, ensuring reliable detection even at lower irradiance levels. Furthermore, it boasts fast switching times, characterized by rise and fall times in the microsecond range, enabling its use in applications requiring quick response, such as data communication links, object detection, and speed sensing.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

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

• Power Dissipation (P_D): 100 mW. This is the maximum power the device can dissipate as heat. 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 with the base open (floating).
• Emitter-Collector Voltage (V_ECO): 5 V. The maximum reverse voltage applicable between the emitter and collector.
• Operating Temperature Range: -40°C to +85°C. The ambient temperature range over which the device is guaranteed to function according to its electrical specifications.
• 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, measured 1.6mm from the package body. This defines the reflow soldering profile constraints.

2.2 Electrical & Optical Characteristics

These parameters define the device's performance under specific test conditions at T_A=25°C.

• Collector-Emitter Breakdown Voltage, V_(BR)CEO: 30 V (Min). Measured at I_C = 1mA with zero irradiance (E_e = 0 mW/cm²).
• 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), tested at I_C = 50μA and E_e = 0.5 mW/cm². A low V_CE(SAT) is desirable for efficient switching.
• Switching Times:
  • Rise Time (T_r): 15 μs (Typ). The time for the output current to rise from 10% to 90% of its final value.
  • Fall Time (T_f): 18 μs (Typ). The time for the output current to fall from 90% to 10% of its initial value. Tested at V_CC=5V, I_C=1mA, R_L=1kΩ.
• Collector Dark Current (I_CEO): 100 nA (Max). The leakage current flowing through the collector when no light is incident (E_e = 0 mW/cm²) and V_CE = 10V. A low dark current is critical for good signal-to-noise ratio in low-light detection.
• On-State Collector Current Ratio (R): Defined as I_L1/I_L2, with a typical value of 1.0 and min/max of 0.8/1.25. This parameter relates to the consistency of current output under specific test conditions.

3. Binning System Explanation

The LTR-5576D employs a binning system based on the average on-state collector current (I_C(ON)). This current is measured under standardized conditions: V_CE = 5V and an irradiance (E_e) of 1 mW/cm². The devices are sorted into different bins (A through F) according to their measured I_C(ON) range. Each bin is associated with a specific color marking for easy identification.

Two sets of limits are provided: the tighter Production Setting ranges used during manufacturing sorting, and the wider Quality Control (Q.C.) Limits used for final acceptance testing.

This binning allows designers to select devices with consistent sensitivity for their specific circuit requirements, ensuring predictable performance in volume production.

4. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate the device's behavior under varying 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. At 25°C, it is in the nanoampere range, but it can increase significantly at the upper end of the operating temperature range (+85°C). This characteristic is crucial for designing circuits that must maintain stability over a wide temperature range, as the increasing dark current acts as an offset or noise source.

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

This graph depicts the derating of the maximum allowable power dissipation as ambient temperature increases. At 25°C, the device can dissipate the full 100 mW. As temperature rises, this maximum power must be reduced linearly to prevent exceeding the junction temperature limit. This curve is essential for thermal management and ensuring reliable operation in elevated temperature environments.

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

This plot demonstrates the relationship between switching speed (T_r, T_f) and the load resistance (R_L) connected to the collector. The switching times decrease as the load resistance decreases. This is because a smaller R_L allows for faster charging and discharging of the phototransistor's junction capacitance and any parasitic capacitances in the circuit. Designers can use this curve to optimize R_L for a desired balance between switching speed and output signal amplitude.

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

This curve shows the phototransistor's transfer function: the relationship between incident infrared irradiance (E_e, in mW/cm²) and the resulting collector current (I_C). The curve is typically linear over a certain range. This linearity is important for analog sensing applications where the output current should be directly proportional to the light intensity. The plot is taken at V_CE = 5V.

5. Mechanical & Package Information

5.1 Package Dimensions

The LTR-5576D comes in a standard 3-pin side-looking package. Key dimensions (in millimeters) are as follows, with a general tolerance of ±0.15mm unless specified otherwise:

• Package Body: Approximately 3.0mm in length, 2.8mm in height, and 1.9mm in depth (excluding leads).
• Lead Spacing: The distance between the centers of the leads is a standard value, measured where they emerge from the package body.
• Protruded Resin: A maximum of 1.5mm of resin may protrude under the flange.

The dark green plastic material of the package is integral to its function, filtering out visible light.

5.2 Polarity Identification

The device has three leads: Emitter, Collector, and Base (often left unconnected or used for a bias resistor in some configurations). The pinout is standard for this package type, but designers must always consult the detailed package drawing in the datasheet for correct orientation. Incorrect connection can damage the device.

6. Soldering & Assembly Guidelines

Handling and assembly of phototransistors require care to avoid damage from electrostatic discharge (ESD) and excessive heat.

• ESD Precautions: The device is sensitive to ESD. Proper ESD-safe handling procedures, including the use of grounded wrist straps and conductive work surfaces, must be followed.
• Reflow Soldering: The absolute maximum rating for lead soldering is 260°C for 5 seconds, measured 1.6mm from the package body. This corresponds to a standard lead-free reflow profile. The profile must be carefully controlled to avoid thermal shock or exceeding this limit.
• Wave Soldering: If used, wave soldering should be performed with appropriate preheating to minimize thermal stress on the plastic package.
• Cleaning: Use cleaning solvents that are compatible with the dark green plastic material to avoid discoloration or degradation.
• Storage: Store in a dry, ESD-protected environment within the specified temperature range of -55°C to +100°C.

7. Application Suggestions

7.1 Typical Application Scenarios

• Object Detection and Proximity Sensing: Used in devices like automatic faucets, hand dryers, paper towel dispensers, and security systems to detect the presence or absence of an object by reflecting an infrared beam.
• Industrial Automation: For counting objects on a conveyor belt, detecting the position of machinery parts, or in optical encoders for speed and position feedback.
• Consumer Electronics: In remote control receivers (though often paired with a dedicated IC), ambient light sensors for display brightness control, and slot sensors in printers or disc drives.
• Basic Data Links: For simple, short-range infrared data transmission (e.g., IrDA compliant systems at lower speeds).

7.2 Design Considerations

• Biasing Circuit: The phototransistor can be used in two common configurations: a simple switch (with a pull-up resistor) or in a linear mode for analog sensing. The value of the load resistor (R_L) is critical and affects gain, bandwidth (switching speed), and output voltage swing.
• Ambient Light Rejection: The dark green package provides significant rejection of visible light, but it is not perfect. For high-ambient-light environments, additional optical filtering, modulated IR signals, or synchronous detection techniques may be necessary to improve signal integrity.
• Temperature Compensation: As shown in the curves, dark current increases with temperature. For precision analog sensing, circuits may need temperature compensation or use of the device in a differential configuration to cancel out the temperature-dependent offset.
• Lens and Housing Design: The field of view of the sensor is determined by its package. External lenses or apertures can be used to focus or restrict the sensing area as needed for the application.

8. Technical Comparison & Differentiation

The LTR-5576D's primary differentiator is its dark green plastic package. Compared to standard clear or colorless packages, this offers inherent filtering of visible light, simplifying optical design in environments with fluctuating ambient visible light. Its fast switching times (in the 15-18 μs range) make it suitable for applications requiring quicker response than typical phototransistors, which can have switching times in the tens to hundreds of microseconds. The comprehensive binning system (Bins A-F) provides designers with a guaranteed sensitivity range, enabling more consistent performance in volume production compared to unbinned parts with wider parameter spreads.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the dark green package?
A: The dark green plastic acts as a built-in optical filter. It attenuates most of the visible light spectrum while allowing infrared wavelengths to pass through to the silicon chip. This significantly reduces the sensor's response to ambient room light, sunlight, or other visible sources, making it respond primarily to the intended infrared signal.

Q: How do I choose the right load resistor (R_L)?
A: The choice involves a trade-off. A larger R_L provides higher output voltage swing for a given photocurrent (higher gain) but results in slower switching speeds (see Fig. 3). A smaller R_L offers faster response but lower gain. Select R_L based on whether your priority is sensitivity (analog sensing) or speed (digital switching).

Q: What does the binning (A-F) mean for my design?
A: Binning ensures sensitivity consistency. If your circuit is designed for a specific current threshold, using devices from the same bin guarantees they will all trigger at approximately the same light level. Mixing bins could cause some units to be more or less sensitive than others. Select a bin whose I_C(ON) range fits your circuit's operating point.

Q: Can I use this sensor in direct sunlight?
A: While the dark green package helps, direct sunlight contains a massive amount of infrared radiation that can saturate the sensor. For outdoor or high-ambient-IR applications, additional measures are needed, such as optical bandpass filters tuned to your specific IR source wavelength, physical shielding, or using a modulated IR source with synchronous detection.

10. Practical Design Case Study

Scenario: Designing a Paper Towel Dispenser Sensor.
The goal is to detect a hand placed under the dispenser and activate the motor. An IR LED emitter is placed opposite the LTR-5576D detector. Normally, the IR beam hits the detector, generating a current. When a hand interrupts the beam, the current drops.

Design Steps:
1. Circuit Configuration: Use the phototransistor in a common-emitter switch configuration. Connect the collector to a supply voltage (e.g., 5V) through a load resistor R_L. The emitter is connected to ground. The output voltage is taken at the collector node.
2. Choosing R_L: Since speed is not critical (hand movement is slow), prioritize a good signal swing. From Fig. 4, at a reasonable irradiance, I_C might be ~500μA (Bin C). Choosing R_L = 10kΩ gives a voltage swing of ΔV = I_C * R_L ≈ 5V, which is excellent for driving a logic input.
3. Binning Selection: Choose a bin (e.g., Bin C or D) that provides sufficient current with the chosen IR LED's output at the required sensing distance. This ensures reliable triggering.
4. Ambient Light Immunity: The dark green package of the LTR-5576D automatically rejects most variations in room lighting, making the system robust without complex filtering.
5. Output Conditioning: The collector voltage (high when beam is present, low when interrupted) can be fed directly into a comparator or microcontroller GPIO pin for processing.

11. Operating Principle

A phototransistor is fundamentally a bipolar junction transistor (BJT) where the base current is generated by light instead of an electrical connection. In the LTR-5576D (NPN type), infrared photons incident on the base-collector junction generate electron-hole pairs. These photogenerated carriers are swept by the electric field across the reverse-biased base-collector junction, creating a photocurrent. This photocurrent acts as the base current (I_B) for the transistor. Due to the transistor's current gain (β or h_FE), the collector current (I_C) is much larger than the original photocurrent (I_C ≈ β * I_B). This internal amplification is what gives a phototransistor its high sensitivity compared to a simple photodiode.

12. Technology Trends

The field of optical sensing continues to evolve. Trends relevant to components like the LTR-5576D include:
Integration: Increasing integration of the photodetector with analog front-end circuitry (transimpedance amplifiers, ADCs) and digital logic into single-chip solutions or modules.
Wavelength Specificity: Development of detectors with sharper spectral response curves or tunability for specific applications like gas sensing or biological analysis.
Miniaturization: Ongoing reduction in package size to fit into ever-smaller consumer and medical devices.
Improved Performance: Efforts to further reduce dark current, enhance speed, and increase sensitivity for low-power applications. The fundamental principle of the phototransistor remains valid, but its implementation and supporting system architecture continue to advance.