LTR-516AD Phototransistor Datasheet - Dark Green Package - 30V Reverse Voltage - 150mW Power Dissipation - Technical Documentation

1. Product Overview

LTR-516AD is a high-performance silicon NPN phototransistor specifically designed for detecting infrared radiation. Its core function is to convert incident infrared light into an electrical current. A key feature of this component is its special dark green plastic package, which is designed to filter out most of the visible light spectrum. This makes it particularly suitable for application scenarios where the sensor must primarily respond to infrared signals, minimizing interference from ambient visible light. The device combines high photosensitivity, low junction capacitance, and fast switching times, making it an ideal choice for various infrared sensing and communication systems.

2. In-depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

To ensure reliability and prevent damage, this device is rated to operate within specific environmental and electrical limits. At an ambient temperature (T_A) of 25°C, the maximum power dissipation is 150 mW. It can withstand a reverse voltage (V_R). The operating temperature range is -40°C to +85°C, while the storage temperature range is -55°C to +100°C. For assembly, the pins can be soldered at 260°C for a maximum duration of 5 seconds, with the solder point at least 1.6mm away from the package body.

2.2 Electrical and Optical Characteristics

All electrical and optical parameters are specified at T_A= 25°C. Under reverse current (I_(BR)R) is 100µA, the reverse breakdown voltage (V_R) is typically 30V. The reverse dark current (I_D(R)), which is the leakage current when no light is incident, reaches a maximum of 30 nA at V_R= 10V. Under an irradiance (E_e) of 0.5 mW/cm² from a 940nm light source, the phototransistor generates an open-circuit voltage (V_OC). Its dynamic performance characteristics are manifested as, at V_r=10V, 940nm pulse, and 1 kΩ load resistance test conditions, the rise and fall times (T_f, T_R) are each 50 nanoseconds. The short-circuit current (I_S) is the key indicator for measuring sensitivity, at V_R=5V, λ=940nm, and E_e=0.1 mW/cm², the typical value is 2 µA. The summary capacitance (C_T) at V_R=3V and 1 MHz is a maximum of 25 pF. The peak spectral sensitivity wavelength (λ_SMAX) is 900 nm.

3. Performance Curve Analysis

The datasheet provides several characteristic curves crucial for circuit design. Figure 1 plots the dark current (I_D) versus reverse voltage (V_R), showing the device's leakage behavior in darkness. Figure 2 illustrates how the junction capacitance (C_T) decreases with increasing reverse voltage, which is very important for high-frequency applications. Figure 3 shows the variation of photocurrent with ambient temperature, indicating that the sensor's output may drift with temperature changes. Figure 4 similarly plots dark current versus temperature. Figure 5 is the relative spectral sensitivity curve, graphically confirming the peak response at 900nm and the effectiveness of the dark green package in attenuating sensitivity in the visible light range. Figure 6 shows the photocurrent (I_p) versus infrared irradiance (E_e) arasındaki doğrusal ilişkiyi göstermektedir. Şekil 7, hassasiyetin açıya bağımlılığını gösteren bir kutupsal diyagramdır. Şekil 8, ortam sıcaklığı 25°C'yi aştığında izin verilen maksimum toplam güç tüketiminin nasıl düşürüleceğini ayrıntılı olarak açıklamaktadır.

4. Mechanical and Packaging Information

LTR-516AD uses a special dark green plastic package. Key dimension specifications include: all dimensions are in millimeters, with a general tolerance of ±0.25mm unless otherwise specified. The maximum resin protrusion under the flange is 1.5mm. Pin pitch is measured at the point where the pins extend from the package body. This package is designed for through-hole mounting. The dark green color is an integral part of its function, acting as a visible light filter to improve the signal-to-noise ratio for infrared detection.

5. Soldering and Assembly Guide

Don tabbatar da amincin walda, bin ƙa'idodin yanayi daidai yana da mahimmanci. Ya kamata a yi wa fil ɗin walda a zafin jiki na 260°C, ba wuce daƙiƙa 5 ba. Dandalin walda dole ne ya kasance aƙalla 1.6mm (0.063 inci) daga jikin kullin filastik, don hana lalacewar zafi ga guntuwar semiconductor da kullin filastik. Idan aka bi matsanancin zafi da lokaci daidai, ana iya amfani da daidaitattun fasahohin walda na igiyar ruwa ko na hannu. Bayyanawa na tsawon lokaci ga zafin jiki fiye da iyakar da aka ƙayyade zai iya rage aiki ko haifar da gazawa ta dindindin.

6. Application Recommendations

6.1 Typical Application Scenarios

LTR-516AD is very suitable for various infrared-based applications. These applications include object detection and proximity sensing in automation and security systems, slot sensors in printers and vending machines, non-contact switches, and infrared data communication links (such as old IRDA interfaces). Its fast switching time makes it suitable for systems that require fast pulse detection.

6.2 Design Considerations

When designing with this phototransistor, several factors must be considered. First, the operating point should be selected based on the required sensitivity and speed; a higher reverse voltage typically reduces capacitance and increases speed but raises the dark current. The load resistor (R_L) value is a critical design choice: a larger R_Lprovides a higher voltage output but slows the response time (increases the RC time constant). The dark green package reduces interference from ambient visible light, but designers should still consider the infrared background in the application environment. For stable operation under temperature variations, the changes shown in Figure 3 and Figure 4 should be considered, potentially necessitating temperature compensation in the signal conditioning circuit.

7. Technical Comparison and Differentiation

The primary differentiating feature of the LTR-516AD is its deep green package, specifically designed to suppress visible light, which is not common among all standard phototransistors. This gives it a significant advantage in environments with fluctuating visible light. Its combination of parameters—a relatively high short-circuit current (typical 2 µA), low capacitance (max 25 pF), and fast switching time (50 ns)—makes it a well-balanced component suitable for high-sensitivity and moderate high-speed applications. Compared to photodiodes, phototransistors like the LTR-516AD provide internal gain, resulting in higher output current for the same light input and simplifying subsequent amplification stages.

8. 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 significantly attenuates wavelengths in the visible spectrum while allowing infrared light (especially near 900-940nm) to pass through. This minimizes the sensor's response to ambient indoor light, sunlight, or other visible light sources, making it more reliable for detecting dedicated infrared signals.

Q: How to understand "Short-Circuit Current (I_S)" parameters?
Answer: I_Sis under the condition of collector and emitter short-circuit (V_CEIt is measured under the condition of zero bias voltage (V = 0V). It represents the photogenerated current per unit irradiance under specific test conditions (940nm, 0.1 mW/cm²). In your circuit, when a load resistor or bias voltage is applied, the actual output current will be less than I_S, but I_Sis a key indicator for comparing the fundamental sensitivity of different devices.

Q: Why are rise time and fall time important?
A: These parameters (T_rand T_f) define the phototransistor's response speed to changes in light intensity. A value of 50 ns means the device can theoretically handle signal frequencies up to several megahertz, making it suitable for pulsed infrared systems, data transmission, or high-speed counting applications.

Q: How does temperature affect performance?
A: As shown by the curve, both the dark current (noise) and the photocurrent (signal) increase with rising temperature. The increase in dark current can be significant and may elevate the noise floor. Designers must ensure the signal conditioning circuit can handle this variation, especially when the device operates across the full temperature range from -40°C to +85°C.

9. Practical Design Cases

Consider designing a simple infrared object detection circuit. The LTR-516AD is paired with an infrared LED emitter. The phototransistor is connected in a common-emitter configuration: the collector is connected to the supply voltage (e.g., 5V) through a load resistor R_L, and the emitter is grounded. When no object is present, infrared light from the LED reaches the phototransistor, causing it to conduct and pulling the collector voltage (V_OUT) is pulled low. When an object interrupts the beam, the phototransistor turns off, and V_OUTgoes high. R_Lmust be chosen based on the required output voltage swing and speed. For a 5V supply and typical I_S=2µA, when illuminated, the 10 kΩ R_Lproduces a voltage drop of approximately 20 mV, which is quite small. Therefore, an operational amplifier comparator stage is typically added after the phototransistor to provide a clean digital output. The dark green package helps suppress ambient light, enabling the system to operate robustly under various lighting conditions.

10. Working Principle

A phototransistor is essentially a bipolar junction transistor (BJT) whose base current is generated by light rather than supplied electrically. In the LTR-516AD (NPN type), incident photons with energy greater than the silicon bandgap generate electron-hole pairs in the base-collector junction region. These photogenerated carriers are swept out by the electric field, effectively creating a base current. This base current is then amplified by the transistor's current gain (β), resulting in a much larger collector current. The device typically operates with the base terminal left floating or disconnected, and a reverse bias is applied across the collector-base junction to widen the depletion region, thereby improving sensitivity and speed.

11. Industry Trends

The field of optical sensing continues to evolve. There is a trend towards integration, combining photodetectors, amplifiers, and digital logic onto a single chip (e.g., integrated ambient light sensors, proximity sensors). For automated assembly, surface-mount device (SMD) packages are becoming increasingly prevalent over through-hole types. Materials and designs are also advancing to improve sensitivity, reduce noise (dark current), and extend spectral range. However, discrete components like the LTR-516AD remain crucial for applications requiring specific performance characteristics, customized optical paths, or high-voltage handling capabilities, which may not be available in integrated solutions. The principle of using filtered packages to achieve specific spectral responses remains a common and effective design practice.