LTR-5888DH Phototransistor Data Sheet - Dark Green Package - 30V Collector-Emitter Voltage - English Technical Documentation

1. Product Overview

The LTR-5888DH is a high-performance infrared (IR) phototransistor designed for sensing applications where reliable detection of infrared light is required. Its primary function is to convert incident infrared radiation into an electrical current. The device is housed in a special dark green plastic package, a key feature that significantly reduces its sensitivity to visible light. This filtering effect minimizes interference from ambient visible light sources, enhancing the signal-to-noise ratio and reliability in dedicated infrared sensing systems. The component is characterized by a wide operating range for the collector current, high sensitivity to IR light, and fast switching times, making it suitable for applications requiring quick response.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The device is rated for operation under specific maximum conditions to ensure reliability and prevent damage. The maximum power dissipation is 100 mW. The collector-emitter voltage (V_CEO) can withstand up to 30V, while the emitter-collector voltage (V_ECO) is limited to 5V. The operational temperature range is from -40°C to +85°C, and it can be stored in environments ranging from -55°C to +100°C. For soldering, the leads can tolerate a temperature of 260°C for 5 seconds when measured 1.6mm from the body of the component.

2.2 Electrical and Optical Characteristics

Detailed performance parameters are specified at an ambient temperature (T_A) of 25°C. The collector-emitter breakdown voltage (V_(BR)CEO) is typically 30V at a collector current (I_C) of 1mA with no irradiance. The collector-emitter saturation voltage (V_CE(SAT)) ranges from 0.1V to 0.4V when the collector current is 100μA under an irradiance of 1 mW/cm². Switching speed is defined by rise time (T_r) and fall time (T_f), specified as 15 μs and 18 μs respectively under test conditions of V_CC=5V, I_C=1mA, and a load resistance (R_L) of 1 kΩ. The collector dark current (I_CEO), which is the leakage current when no light is present, is between 0.1 nA and 100 nA at V_CE=10V.

3. Binning System Explanation

The LTR-5888DH employs a binning system to categorize devices based on their On-State Collector Current (I_C(ON)). This parameter is the average current generated by the phototransistor under standardized conditions (V_CE = 5V, E_e = 1 mW/cm²). The datasheet provides two sets of binning tables: one for the "Setting of Production" and another for the guaranteed "On State Collector Current Range."

Each bin (A through H) corresponds to a specific range of I_C(ON) and is identified by a color marking on the component. For example, Bin A (marked Red) in the production setting has an I_C(ON) range of 0.20 mA to 0.26 mA, while its guaranteed range is 0.16 mA to 0.31 mA. This binning allows designers to select components with consistent sensitivity for their specific circuit requirements, ensuring predictable performance in volume production. The bins progress from lower sensitivity (Bin A) to higher sensitivity (Bin H).

4. Performance Curve Analysis

The datasheet includes several characteristic curves that illustrate device behavior under varying 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 critical consideration for high-temperature applications, as increased leakage current can affect the off-state signal level and noise floor of the sensing circuit.

4.2 Collector Power Dissipation vs. Ambient Temperature

Figure 2 depicts the derating curve for maximum allowable collector power dissipation (P_C). As ambient temperature increases, the maximum safe power dissipation decreases linearly. This graph is essential for thermal management and ensuring the device operates within its safe operating area (SOA).

4.3 Rise and Fall Time vs. Load Resistance

Figure 3 demonstrates the relationship between switching speed (rise time T_r and fall time T_f) and the load resistance (R_L). Both T_r and T_f increase with higher load resistance. Designers can use this curve to optimize the trade-off between switching speed and output voltage swing by selecting an appropriate R_L value.

4.4 Relative Collector Current vs. Irradiance

Figure 4 plots the relative collector current against infrared irradiance (E_e). The curve shows a sub-linear relationship, where the rate of increase in collector current diminishes at higher irradiance levels. This characteristic defines the phototransistor's sensitivity and dynamic range.

5. Mechanical and Package Information

The component uses a standard phototransistor package. Key dimensional notes include: all dimensions are in millimeters, with a general tolerance of ±0.25mm unless specified otherwise. The maximum protrusion of resin under the flange is 1.5mm. Lead spacing is measured at the point where the leads exit the package body. The dark green plastic material is specifically chosen for its optical filtering properties.

6. Soldering and Assembly Guidelines

The leads can be soldered at a maximum temperature of 260°C for a duration not exceeding 5 seconds. This should be measured at a distance of 1.6mm (0.063 inches) from the package body to prevent thermal damage to the semiconductor die inside. Standard wave or reflow soldering processes compatible with this thermal profile can be used. Care should be taken to avoid excessive mechanical stress on the leads during handling and placement.

7. Application Recommendations

7.1 Typical Application Scenarios

The LTR-5888DH is ideal for various infrared detection applications, including object detection and counting, slot sensors (e.g., in printers or vending machines), proximity sensing, and industrial automation where a beam-break principle is used. Its dark green package makes it particularly suitable for environments with high ambient visible light, such as under daylight or bright indoor lighting.

7.2 Design Considerations

When designing a circuit, the load resistor (R_L) value is crucial. A smaller R_L provides faster switching (as seen in Figure 3) but results in a smaller output voltage swing for a given photocurrent. A larger R_L gives a larger voltage swing but slower response. The operating voltage should not exceed the absolute maximum ratings. The binning selection should align with the required sensitivity for the application's expected IR signal strength. For stable operation, consider the temperature dependence of the dark current, especially in high-temperature environments.

8. Technical Comparison and Differentiation

The primary differentiating feature of the LTR-5888DH is its dark green package. Compared to standard clear or colorless packages, this package acts as a built-in visible light filter. This eliminates or reduces the need for an external optical filter, simplifying assembly, reducing component count, and potentially lowering cost. Its combination of high sensitivity, fast switching, and a wide collector current range makes it a versatile choice among infrared phototransistors.

9. Frequently Asked Questions (FAQ)

Q: What is the purpose of the dark green package?
A: The dark green plastic filters out a significant portion of visible light, allowing primarily infrared light to reach the phototransistor's sensitive area. This improves performance in environments with bright ambient light by reducing false triggers or noise.

Q: How do I select the right bin for my application?
A: Choose a bin based on the expected infrared signal strength in your application. If the IR source is weak or distant, a higher-sensitivity bin (e.g., H, Orange) may be necessary. For strong signals, a lower-sensitivity bin (e.g., A, Red) might suffice and could offer benefits like lower dark current. Always consult the guaranteed current range, not just the production setting range.

Q: Why does switching speed depend on the load resistor?
A> The load resistor and the phototransistor's internal capacitance form an RC circuit. A larger resistor increases the RC time constant, slowing down the charging and discharging of this capacitance during switching events, thus increasing rise and fall times.

10. Practical Application Case

Case: Paper Detection in an Office Printer
In a printer paper tray sensor, an infrared LED is placed on one side of the paper path, and the LTR-5888DH is placed directly opposite. When paper is present, it blocks the IR beam, causing the phototransistor's current to drop. The dark green package is critical here because printers are often used in well-lit offices. It prevents fluorescent or LED room lights from being misinterpreted as the IR signal from the LED, ensuring reliable paper-out detection. A medium-sensitivity bin (e.g., C or D) would typically be selected, and a load resistor value would be chosen to provide a clean digital output signal to the printer's microcontroller with an appropriate response time for paper movement.

11. Operating Principle

A phototransistor operates similarly to a standard bipolar junction transistor (BJT) but with a light-sensitive base region. Instead of a base current, incident photons (light particles) generate electron-hole pairs in the base-collector junction when their energy is sufficient. 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 original photocurrent, providing high sensitivity. The LTR-5888DH is optimized to respond to photons in the infrared wavelength range.

12. Technology Trends

The trend in discrete optical sensors like phototransistors is towards greater integration, smaller packages, and enhanced functionality. While discrete components remain vital for cost-sensitive or specific-performance applications, there is a move towards integrated solutions that combine the photodetector, amplifier, and sometimes a digital interface (like I2C) into a single package. These integrated sensors offer calibrated digital outputs and can be easier to use but may come at a higher cost. For pure, high-speed, or analog sensing needs, discrete phototransistors like the LTR-5888DH continue to be a reliable and effective solution. The use of specialized package materials for optical filtering, as seen here, is a key method to improve performance without increasing circuit complexity.