LTR-S320-TB-L Side-Looking Infrared Phototransistor Datasheet - 940nm Peak Wavelength - Technical Documentation

1. Product Overview

The LTR-S320-TB-L is a discrete infrared phototransistor specifically designed for near-infrared spectrum sensing applications. It belongs to a broad family of optoelectronic components suitable for systems requiring reliable infrared detection. This device is engineered to convert incident infrared radiation into a corresponding electrical signal at its output.

The core function of this component is based on the photoelectric effect within a semiconductor junction. When infrared light with sufficient energy (corresponding to its peak sensitivity wavelength) irradiates the photosensitive area, electron-hole pairs are generated. In a phototransistor, this photocurrent is internally amplified, resulting in a collector current significantly larger than that of a simple photodiode, making it suitable for detecting lower light levels or for use in simpler circuits.

Its primary design objectives include compatibility with modern automated assembly processes, robustness to withstand infrared reflow soldering, and a form factor that facilitates integration into space-constrained printed circuit board (PCB) layouts.

1.1 Features

• Compliant with the RoHS (Restriction of Hazardous Substances) directive and classified as a green product.
• Utilizes a side-view package configuration with a dark epoxy dome lens. The side-view orientation allows the sensor to detect infrared signals parallel to the PCB plane, which is useful for edge-sensing applications or when the infrared light source is not perpendicular to the board.
• The dark lens material helps attenuate visible light, reducing interference from ambient light sources and improving the signal-to-noise ratio for infrared signals.
• Provided in 8mm carrier tape format, wound on 7-inch diameter reels, suitable for high-speed, automated surface-mount assembly equipment.
• Package and materials are designed to withstand the standard infrared (IR) reflow soldering temperature profiles used in Surface-Mount Technology (SMT) assembly lines.
• Complies with EIA (Electronic Industries Alliance) standard package outlines, ensuring mechanical compatibility with industry-standard pad sizes and handling equipment.

1.2 Applications

• Infrared Receiver Module:Primarily used as a sensing element in the receiver of remote control systems (e.g., TVs, audio equipment, air conditioners). It detects modulated infrared signals from remote controllers.
• PCB-Mount Infrared Sensor:Directly integrated onto the PCB for proximity sensing, object detection, or data transmission in devices such as smartphones, tablets, home appliances, and industrial equipment.
• Security and Alarm Systems:Can be used in beam interruption sensors or reflective object sensors for intrusion detection.
• Industrial Automation:Used in devices on assembly lines for counting, positioning, or detecting the presence/absence of objects.

2. Detailed Technical Parameters

This section provides a detailed and objective interpretation of the key electrical and optical parameters that define the performance and operational limits of the LTR-S320-TB-L phototransistor.

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device. Operation at or near these limits is not guaranteed and should be avoided in reliable designs.

• Power Dissipation (Pd):75 mW maximum at an ambient temperature (Ta) of 25°C. This is the maximum heat the device can dissipate without exceeding its thermal limits. The derating curve (Figure 2 in the datasheet) shows how this rating decreases with increasing ambient temperature.
• 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 that can be applied between the emitter and collector.
• Operating Temperature Range:-40°C to +85°C. The ambient temperature range over which the device is specified to operate normally.
• Storage Temperature Range:-55°C to +100°C. The temperature range for storing the device when it is not powered.
• Infrared Soldering Conditions:Peak temperature tolerance of 260°C for up to 10 seconds. This defines its compatibility with lead-free (Pb-free) reflow soldering processes.

2.2 Electrical and Optical Characteristics

These are typical and guaranteed performance parameters measured under specific test conditions at 25°C.

• Peak sensing wavelength (λ_p):940 nm. The infrared wavelength to which the phototransistor is most sensitive. It achieves optimal matching with the emission wavelength of common 940nm GaAs infrared emitting diodes (IREDs).
• Collector dark current (I_CEO):At V_CE=20V, E_eUnder the condition of =0 mW/cm², the maximum is 100 nA. This is the small leakage current flowing through the collector when there is no infrared light irradiation (dark condition). Lower dark current is generally beneficial for sensitivity to weak signals.
• On-state collector current (I_C(ON)):At V_CE=5V, using a 940nm light source and an irradiance (E_e) of 0.5 mW/cm², typical value is 2.0 mA, minimum value is 1.0 mA. This parameter indicates the output current level under a given standard input light intensity. The test tolerance is ±15%.
• Collector-emitter saturation voltage (V_CE(SAT)):At I_C=100µA, E_e=0.5 mW/cm², the maximum is 0.4 V. This is the voltage drop across the transistor when it is fully "on" (saturated) under the specified low current condition.
• Rise time (T_r) and fall time (T_f):At V_CE=5V, I_C=1mA, R_L=1kΩ, typical values are both 15 µs. These parameters define the switching speed of the phototransistor—the speed at which the output current responds to a step change in light, rising from 10% to 90% of the final value (rise time) and falling from 90% to 10% (fall time). This speed is suitable for standard remote control protocols (e.g., 36-40kHz carrier).

3. Performance Curve Analysis

The datasheet contains several graphs illustrating how key parameters vary with operating conditions. Understanding these curves is crucial for robust circuit design.

3.1 Spectral Sensitivity (Figure 5)

This curve plots the relative sensitivity of the phototransistor across a range of wavelengths. It confirms peak sensitivity at 940nm and shows a significant drop in sensitivity at shorter (visible) and longer (far-infrared) wavelengths. The dark lens helps attenuate sensitivity in the visible spectrum, thereby reducing ambient light noise.

3.2 Relative Collector Current vs. Irradiance (Figure 3)

This graph shows the relationship between the output collector current and the incident infrared optical power density (irradiance). It is typically linear over a certain range, indicating that the output current is proportional to the light intensity, which is ideal for analog sensing applications. This curve helps designers determine the expected output for a given light input.

3.3 Collector Dark Current vs. Temperature (Figure 1) and Power Derating (Figure 2)

Figure 1 shows that the dark current (I_CEO) increases exponentially with rising ambient temperature. This is a key consideration in high-temperature applications, as the increased dark current raises the noise floor and can reduce effective sensitivity. Figure 2 shows the derating of the maximum allowable power dissipation with increasing ambient temperature. Above 25°C, the power the device can safely handle decreases because its ability to dissipate heat to the environment is reduced.

3.4 Rise/Fall Time vs. Load Resistance (Figure 4)

Wannan lanƙwasa yana nuna ma'auni na asali a cikin ƙirar da'irar transistor na haske. Saurin sauyawa (lokacin tashi/faɗuwa) ya dogara sosai akan resistor ɗin kaya (R) da aka haɗa zuwa taro._L). Babban R_Lyana ƙara girman fitarwar ƙarfin lantarki, amma kuma yana ƙara ƙimar lokacin RC, wanda ke rage saurin amsawa. Ƙaramin R_Lyana ba da damar saurin sauyawa mafi sauri, amma ƙaramin siginar fitarwa. Dole ne mai ƙira ya zaɓi R bisa ga ko sauri ko girman siginar ya fi mahimmanci a aikace-aikacen su._L。

4. Mechanical and Packaging Information

4.1 Outline Dimensions

Na'urar tana amfani da kunshe na kallon gefe, mai hawa saman. Mahimman girmansu sun haɗa da girman jiki, tazarar ƙusa, da wurin ruwan tabarau. Ana ba da duk mahimman girmansu a cikin milimita, da daidaitaccen ƙima na ±0.1mm, sai dai idan an faɗi daban. An nuna shugaban kallon gefe a cikin zane a sarari.

4.2 Polarity Identification

Wannan kayan yana da fil biyu. Takardar ƙayyadaddun bayanai ta nuna wane fil ne Collector, kuma wane ne Emitter. Dole ne a kula da daidaitaccen polarity yayin haɗa PCB. Yawanci, mafi tsayin fil (idan yana cikin kayan marufi na kayan aiki) ko kuma alamar kusurwa a kan kayan aiki tana nuna Collector.

4.3 Recommended Land Pattern (Section 6)

An ba da shawarar hotunan gindin solder na PCB (girman kunshe). Wannan ya haɗa da girman gindi, tazara, da siffa, don tabbatar da ingantaccen haɗin solder bayan reflow. Ana ba da shawarar yin amfani da allurar ƙarfe mai kauri na 0.1mm (4 mils) ko 0.12mm (5 mils) don buga man gubar.

5. Soldering and Assembly Guide

5.1 Reflow Soldering Temperature Profile

An ba da shawarar cikakkiyar siffar zafin reflow ta infrared don tsarin haɗawa maras gubar (Pb-free). Muhimman ma'auni sun haɗa da:

• Dumama kafin:Heat up to 150-200°C.
• Soak/Preheat Time:Maximum 120 seconds.
• Peak Temperature:Maximum 260°C.
• Time Above Liquidus (TAL):Time within ±5°C of peak temperature should not exceed 10 seconds. Under these conditions, the device should not be subjected to more than two reflow soldering cycles.

This temperature profile is based on JEDEC standards to ensure reliable soldering while preventing damage to the component's epoxy encapsulation or internal structure.

5.2 Manual soldering

If manual soldering is necessary, a soldering iron with a temperature not exceeding 300°C should be used. The contact time per pin should be limited to a maximum of 3 seconds per solder joint.

5.3 Storage and handling

• Sealed Packaging:Devices are shipped in moisture barrier bags with desiccant. They should be stored in an environment with a temperature ≤30°C and relative humidity ≤60%. Once the sealed bag is opened, the components are considered moisture-sensitive.
• Floor Life:After opening the original packaging, it is recommended to complete the infrared reflow soldering process within one week (168 hours).
• Long-Term Storage / Baking:For components stored for more than one week after opening, they should be kept in a sealed container with desiccant. If exposure exceeds this period, baking at 60°C for at least 20 hours before soldering is required to remove absorbed moisture and prevent "popcorn" effect (package cracking) during reflow soldering.

5.4 Cleaning

If cleaning of flux residues is required, isopropyl alcohol or similar alcohol-based solvents are recommended. Harsh or corrosive chemical cleaners should be avoided.

6. Packaging and ordering information

6.1 Carrier Tape and Reel Specifications

The component is supplied on standard 7-inch (178mm) diameter reels. Key packaging details include:

• Carrier tape width: 8mm.
• Quantity per reel:3000 units.
• Minimum Order Quantity (MOQ):Minimum order starts from remaining 500 units.
• Cover tape coverage:Empty component carrier pocket is sealed with cover tape.
• Missing component:According to packaging standards, a maximum of two consecutive missing components is allowed.
• Packaging complies with ANSI/EIA-481-1-A specification.

7. Application Design Considerations

7.1 Drive Circuit Configuration

A phototransistor is a current output device. The most common circuit configuration is to connect it in a common-emitter setup:

• Emitter grounded.
• The collector is connected to the positive power supply voltage (V_CC) through a load resistor (R_L).
• The output signal is taken from the collector node. When light illuminates the sensor, the transistor turns on, pulling the collector voltage low (towards V_CE(SAT)). Under dark conditions, the transistor is off, and the collector voltage is high (pulled up to V_CCCC through R_L).

R_LThe value of R is crucial and requires a trade-off between output voltage swing, response speed (see Figure 4), and power consumption. A typical starting value is 1kΩ to 10kΩ.

7.2 Improving Signal-to-Noise Ratio (SNR)

• Optical Filtering:The built-in dark lens provides a certain filtering function. For environments with strong ambient light, an additional external infrared bandpass filter with a center wavelength of 940nm can be used to block unwanted light.
• Electrical Filtering:Since many infrared remote controls use a modulated carrier frequency (e.g., 38kHz), incorporating a bandpass filter tuned to this frequency in the subsequent amplifier stage can significantly improve the signal-to-noise ratio by suppressing DC ambient light and low-frequency noise.
• Shielding:Mechanically shielding the sensor from direct exposure to ambient light sources (e.g., sunlight, room lights) can reduce noise.

7.3 Haɗawa da Infrared Emitter

For reflective or proximity sensing applications, pair the LTR-S320-TB-L with an infrared LED emitting at or near 940nm. Ensure the emitter's drive current is sufficient to generate the required reflected signal at the detector. Pulsing the emitter and synchronously detecting the phototransistor's output helps distinguish the signal from ambient light.

8. Kwatancen Fasaha da Bambance-bambance

Compared to standard photodiodes, the LTR-S320-TB-L phototransistor provides inherent current gain (β/h_FE), delivering a larger output signal for the same light input. This simplifies circuit design as it typically requires less subsequent amplification. However, this gain comes at the cost of slower response time (microseconds versus nanoseconds for photodiodes) and higher dark current. The side-view package differentiates it from top-view sensors, offering design flexibility for sensing along PCB edges. Its compatibility with automated SMT assembly and standard reflow temperature profiles makes it a cost-effective choice for high-volume manufacturing compared to through-hole alternatives.

9. Tambayoyin da ake yawan yi (FAQ)

9.1 Menene aikin ruwan tabarau mai duhu?

The dark epoxy lens acts as a visible light filter. It attenuates light in the visible spectrum while allowing infrared wavelengths (around 940nm) to pass. This reduces the sensor's sensitivity to ambient indoor light, fluorescent lamps, and sunlight, thereby minimizing noise and improving the reliability of detecting the target infrared signal.

9.2 How to select the value of the load resistor (R_L)?

Selection involves trade-offs. Use Figure 4 in the datasheet as a guide. Formaximum speed(fastest rise/fall time), choose a smaller R_L(e.g., 1kΩ or less). Formaximum output voltage swing(higher signal amplitude), choose a larger R_L(e.g., 10kΩ or greater), but this will slow the response. Ensure that when the transistor is on, R_LVoltage drop across both ends (I_C(ON)* R_L) does not exceed your supply voltage minus V_CE(SAT).

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9.3 Can this sensor be used outdoors?

Ta hanyar ƙira mai kyau, ana iya amfani da shi a waje. Hasken rana kai tsaye yana ɗauke da babban adadin hasken infrared, wanda zai iya cika firikwensin ko haɗa ƙara. Tacewar gani mai inganci (narrowband 940nm bandpass filter), kayan ɗaki masu dacewa don toshe hasken rana kai tsaye, da fasahar gano siginar daidaitawa, suna da mahimmanci ga aiki mai dogaro a waje.

9.4 Why is baking required before soldering if the bag has been opened for more than a week?

Kayan haɗin epoxy na filastik yana ɗaukar ruwa daga iska. A lokacin aikin haɗa guduma mai zafi, wannan ruwan da aka kama zai yi tururi da sauri, yana haifar da matsi mai yawa a ciki. Wannan na iya haifar da fashewar kayan ɗaki ko rabuwa, wannan kuskuren ana kiransa "popcorn" phenomenon. Yin gasa a 60°C zai iya kawar da wannan ruwan da aka ɗauka, yana ba da damar kayan haɗin yin haɗa guduma cikin aminci.

10. Practical Design Example

1. Scenario: Designing a simple infrared proximity sensor for a toy.Objectives:
2. Detect whether an object is within approximately 5 centimeters of the sensor.Components:
3. LTR-S320-TB-L phototransistor, 940nm infrared LED, microcontroller (MCU).Circuit:_LThe phototransistor is connected to V_CC= 4.7kΩ. Its collector output is connected to the MCU's analog-to-digital converter (ADC) pin. An infrared LED is placed next to the phototransistor and is driven by an MCU output pin through a current-limiting resistor (e.g., for 20mA).
4. (3.3V). Its collector output is connected to the MCU's analog-to-digital converter (ADC) pin. An infrared LED is placed next to the phototransistor and is driven by an MCU output pin through a current-limiting resistor (e.g., for 20mA).Operation:
5. The MCU drives the infrared LED with short pulses at a specific frequency (e.g., 1kHz). It then reads the ADC value from the phototransistor. When no object is present, the reflected signal is low. When an object is within range, infrared light reflects back to the phototransistor, causing a measurable increase in the ADC reading. A threshold is set in the MCU software to detect proximity.Considerations:_LThe sensor must be shielded from ambient infrared light sources. The pulsed measurement technique helps distinguish the signal from ambient light. Choose R