LTR-S320-DB-L Phototransistor Datasheet - EIA Standard Package - 940nm Peak Sensitivity - Simplified Chinese Technical Documentation

1. Product Overview

LTR-S320-DB-L is a high-performance silicon NPN phototransistor specifically designed for infrared sensing applications. This component is optimized for near-infrared spectrum detection, with its peak sensitivity at 940nm, making it suitable for a wide range of remote control systems, object detection, and industrial automation tasks. Its primary function is to convert incident infrared light into a corresponding electrical current.

The device is housed in an EIA-standard compliant package, featuring a black daylight-cut resin lens. This lens effectively filters out visible ambient light, significantly reducing noise and false triggering, thereby improving the signal-to-noise ratio under background illumination. The package design is compatible with high-volume automated assembly processes, including tape-and-reel feeding and infrared reflow soldering, meeting modern manufacturing requirements.

As a RoHS-compliant and lead-free "green product," it meets contemporary environmental standards. The combination of its spectral response, package design, and manufacturing compatibility makes it a reliable and versatile solution for cost-sensitive yet performance-driven infrared detection circuits.

2. Technical Parameters: An In-Depth and Objective Interpretation

All electrical and optical characteristics are specified at an ambient temperature (T_A) of 25°C, providing a standardized benchmark for performance evaluation.

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device. Operation at or beyond these limits is not guaranteed, and circuit design should avoid them.

• Power Dissipation (P_D):150 mW. This is the maximum allowable 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 terminals when the base is open (the phototransistor is in the dark state).
• Operating temperature range:-40°C to +85°C. The device is designed to operate normally within this ambient temperature range.
• Storage temperature range:-55°C to +100°C. The temperature range for storing the device in a non-operating state without degradation.
• Infrared soldering conditions:Peak temperature 260°C, maximum 10 seconds. This defines the thermal profile limits for lead-free reflow soldering processes.

2.2 Electrical and Optical Characteristics

These parameters define the device's performance under specific test conditions.

• Reverse breakdown voltage (V_(BR)R):Minimum value 33V, typical value 170V (at I_R=100µA condition). This high value indicates a robust junction structure capable of withstanding significant reverse bias, which is beneficial for circuits with inductive loads or voltage spikes.
• Reverse dark current (I_D):Maximum 10 nA (at V_R=10V condition). This is the leakage current when no light is incident. Low dark current is crucial for achieving high sensitivity and low-noise operation, especially in low-light detection scenarios.
• Open-circuit voltage (V_OC):Typical value 390 mV (under 940nm light irradiation, irradiance E_e=0.5 mW/cm²). This parameter is relevant when the device is used in photovoltaic mode (without external bias).
• Short-circuit current (I_SC):Typical value 1.8 µA (test condition same as V_OCsame, i.e., V_R=5V, λ=940nm, E_e=0.5 mW/cm²). This indicates the photocurrent generated when the output is short-circuited.
• Rise time (T_r) and fall time (T_f):both have a maximum value of 30 ns (V_R=10V, R_L=1kΩ). These switching speed specifications are crucial for applications requiring fast pulse detection or high-frequency modulation, such as data communication links.
• Total capacitance (C_T):Maximum 1 pF (V_R=5V, f=1MHz). Low junction capacitance is essential for maintaining fast response times, as it limits the circuit's RC time constant.
• Spectral bandwidth (λ_0.5):750 nm to 1100 nm. This defines the wavelength range over which the device responsivity is at least half of its peak value. It covers the common infrared region used by many infrared emitters, such as 850nm and 940nm LEDs.
• Peak sensitivity wavelength (λ_P):940 nm. The device is spectrally matched to infrared LEDs emitting at 940 nm, ensuring maximum efficiency and signal strength in such pairings.

3. Performance Curve Analysis

The datasheet references typical characteristic curves, which visually illustrate the device's behavior under various conditions. Although the specific charts are not reproduced in the text, their typical implications are analyzed as follows.

3.1 IV (Current-Voltage) Characteristics

A set of curves, plotted under different levels of incident irradiance (E_C), depicting the collector current (I_CE) with collector-emitter voltage (V_e) relationship. These curves typically show that for a fixed irradiance, I_Cincreases with V_CEuntil reaching the saturation region. Higher irradiance levels shift the curve upward, indicating greater photocurrent. The slope in the active region is related to the output conductance of the device.

3.2 Relationship Between Relative Sensitivity and Wavelength

This curve graphically represents the spectral response, peaking at 940nm and gradually attenuating towards 750nm and 1100nm (λ_0.5points). This is crucial for selecting the appropriate infrared emitter to pair with the detector and for evaluating the impact of environmental light sources with different spectra.

3.3 Temperature Dependence

The curve likely shows key parameters such as dark current (I_D) and photocurrent varying with ambient temperature. Dark current typically increases exponentially with temperature (approximately doubling every 10°C), which can be a significant noise source in high-temperature applications. Photocurrent may also have a slight negative temperature coefficient.

4. Mechanical and Packaging Information

4.1 Package Dimensions

This device conforms to the standard EIA package outline. All dimensions are provided in millimeters, with a standard tolerance of ±0.10 mm unless otherwise specified. The package employs a black daylight-cut resin lens covering the silicon chip.

4.2 Polarity Identification and Pin Definition

The phototransistor is a 2-pin device. The pin definition for this package is standard: the collector is typically connected to the case or the longer lead (if applicable), while the emitter is the other pin. The datasheet diagram provides clear identification. Correct polarity is crucial for the proper operation of the circuit.

4.3 Recommended Pad Layout

Recommended pad patterns (package dimensions) for PCB design are provided to ensure reliable solder joint formation during reflow soldering. Adhering to these dimensions helps prevent tombstoning, misalignment, or insufficient solder fillets.

5. Soldering and Assembly Guide

5.1 Reflow Soldering Temperature Profile

Provides detailed recommendations for infrared reflow soldering temperature profiles suitable for lead-free soldering processes. Key parameters include:

• Preheating:150°C to 200°C.
• Preheating time:Maximum 120 seconds.
• Peak Temperature:Maximum 260°C.
• Time Above Liquidus (at Peak):Mafi tsawon lokaci shine dakika 10.
• Matsakaicin adadin koma-baya: Two.

Wannan lanƙwasa ya dogara ne akan ma'aunin JEDEC don tabbatar da cikakkiyar haɗin kai. Dole ne injiniyoyi su siffanta yanayin zafin jikinsu bisa ga ƙirar PCB, kayan aiki, da kuma man gini na musamman.

5.2 Manual soldering

Idan dole ne a yi walda da hannu, zafin ƙarfen walda bai kamata ya wuce 300°C ba, kuma lokacin walda kowane ƙusa ya kamata a iyakance zuwa mafi tsawon dakika 3. Ana ba da shawarar yin zagaye ɗaya kawai na walda da hannu don guje wa matsin lamba na zafi.

5.3 Tsarkakewa

Only specified cleaning agents should be used. Isopropyl alcohol (IPA) or ethanol is recommended. The device should be immersed at room temperature for less than one minute. Unspecified chemical liquids may damage the package resin.

5.4 Yanayin Ajiya

Sealed Packaging (Moisture Barrier Bag):Store at ≤30°C and ≤90% RH. Use components within one year from the bag sealing date.

Opened Packaging:Store at ≤30°C and ≤60% RH. Components should be reflow soldered within one week (168 hours). For storage outside the original bag for longer periods, they must be stored in a sealed container with desiccant or in a nitrogen dry box. Components stored for more than one week should be baked at approximately 60°C for at least 20 hours prior to soldering to remove absorbed moisture and prevent "popcorning" during reflow.

6. Packaging and Ordering Information

6.1 Tape and Reel Specifications

The device is supplied in 8mm carrier tape, wound on 7-inch (178mm) diameter reels, compatible with standard automatic placement equipment.

• Quantity per reel: 3000.
• Cover tape:Empty component pockets are sealed with top cover tape.
• Missing component:According to reel specifications, a maximum of two consecutive missing components ("missing LEDs") is allowed per reel.
• Standard:Packaging complies with the ANSI/EIA 481-1-A-1994 specification.

7. Application Recommendations

7.1 Typical Application Scenarios

• Infrared Remote Control Receiver:For televisions, audio systems, and set-top boxes (paired with a 940nm infrared LED).
• Object/Proximity Detection:Used in printers, copiers, vending machines, and industrial automation to sense paper, objects, or position.
• Smoke detector:Used in designs based on optical cavities.
• Encoder:For speed or position sensing in motor control.
• Basic optocoupler:For low-speed, cost-sensitive optocoupler circuits.

7.2 Circuit Design Considerations

Driving Method:A phototransistor is a current output device. To achieve consistent performance, especially when multiple devices are used in parallel, it is strongly recommended to connect a current-limiting resistor in series with each phototransistor (Circuit Model A in the datasheet).

Circuit Model A (Recommended):Each phototransistor has its own series resistor connected to the supply voltage. This ensures each device operates at a defined current point, compensating for minor differences in its current-voltage (I-V) characteristics and prevents one device from "hogging" most of the current.

Circuit Model B (Not Recommended for Parallel Connection):Multiple phototransistors are directly connected in parallel to a shared resistor. Due to natural variations in the I-V curves of individual elements, one device may draw more current than others, leading to uneven brightness or sensitivity in detection applications.

Bias:This device is typically used in a common-emitter configuration with a pull-up resistor connected to the collector. The value of this load resistor (R_L) affects both the output voltage swing and the response speed (via the RC time constant formed with the device capacitance). A smaller R_Lprovides a faster response but results in a smaller output voltage change.

Noise Immunity:The black daylight cut-off lens provides excellent visible light suppression. However, in high-noise environments (e.g., with fluorescent lights or sunlight), additional electrical filtering (e.g., a capacitor in parallel with the load resistor or hardware/software debounce algorithms) may be required to suppress modulation interference.

8. Technical Comparison and Differentiation

Compared to simple photodiodes, phototransistors provide internal current gain (the transistor's beta value), resulting in higher output current at the same incident light level. This makes it easier to interface directly with logic circuits or microcontrollers without the need for subsequent amplification stages, simplifying the design and reducing the number of components.

然而，这种增益的代价是响应速度较慢（光电晶体管通常为几十到几百纳秒，而光电二极管为纳秒级）以及可能更高的电容。对于非常高速的应用（例如，>1 MHz调制），带有外部跨阻放大器的光电二极管可能是更好的选择。

Key differentiating factors for the LTR-S320-DB-L within the phototransistor category include: its standardized EIA package for manufacturing ease, specific 940nm spectral matching, integrated daylight filter lens, and its qualification for lead-free reflow processes.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 What is the function of the "Daylight Cut-off" lens?

The black resin lens is doped to be opaque to visible light but transparent to infrared wavelengths around 940nm. This greatly reduces the photocurrent generated by indoor ambient light, sunlight, or other visible light sources, minimizing false triggering and improving the reliability of infrared signal detection.

9.2 Ina iya haɗa shi da LED infrared na 850nm?

Yes, but with reduced efficiency. The device's spectral response curve shows significant sensitivity at 850nm (within the 750-1100nm bandwidth), but it is not the peak (940nm). The output signal will be weaker compared to using a matched 940nm emitter. For optimal performance and maximum range, pairing with a 940nm light source is recommended.

9.3 Yaya ake lissafin ƙimar resistor da ya dace a jere?

Ƙimar resistor ta dogara da ƙarfin aiki da ake buƙata da ƙarfin lantarki (V_CC). A cikin takamaiman haske, phototransistor yana aiki kamar tushen wutar lantarki. Yi amfani da dokar Ohm: R = (V_CC- V_CE(sat)) / I_C. V_CE(sat)is the saturation voltage (typically a few hundred mV at moderate currents). I_Cis the desired collector current, which can be based on I_SCAn estimation is made based on parameters and expected illumination levels. Starting from a typical I_SCvalue (1.8 µA at 0.5 mW/cm²) and scaling according to the irradiance of your application. Select R to set the operating point in the desired region of the IV curve.

9.4 Why is baking required if components are stored outside the moisture barrier bag?

Plastic packages absorb moisture from the atmosphere. During the high-temperature reflow soldering process, this trapped moisture rapidly vaporizes, creating high internal pressure. This can lead to package delamination from the die ("popcorn" effect) or internal cracks, resulting in immediate or latent failures. Baking drives out this absorbed moisture, allowing the components to be safely reflow soldered.

10. Working principle

A phototransistor is essentially a bipolar junction transistor (BJT) whose base current is generated by light rather than an electrical connection. Incident photons with energy greater than the silicon bandgap generate electron-hole pairs in the base-collector junction region. These carriers are swept out by the internal electric field, generating a photocurrent that acts as the base current (I_B). This photogenerated base current is then amplified by the transistor's current gain (h_FEor β) amplification, resulting in a much larger collector current (I_C= β * I_B). The output is taken from the collector terminal, with the emitter grounded. The absence of a physical base pin is a common feature, although some phototransistors include a base connection for bias control or speed optimization.

11. Development Trends

The field of photoelectric detection continues to evolve. Trends related to devices such as the LTR-S320-DB-L include:

• Miniaturization:Develop phototransistors with smaller package sizes (e.g., chip-scale packages) to enable denser electronic devices.
• Enhanced Integration:Integrate photodetectors with amplification, filtering, and digital logic on a single chip to create "smart sensors" with digital outputs (I2C, SPI), reducing the number of external components and simplifying system design.
• Gargajiya sauri:Bincika tsarin da kayan aiki don rage lokacin zirga-zirgar masu ɗaukar kaya da ƙarfin ajiya, don haɓaka bandwidth na transistor na haske don aikace-aikacen sadarwar bayanai.
• Takamaiman tsawon zango:Kera detectors na da ke da kunkuntar amsa na bakan haske daidai, don inganta zaɓi a cikin yanayin tushen infrared da yawa, ko kuma don samar da sabbin hanyoyin ji.
• Kulawa da aminci da gwaji:Yayin da fasahar lantarki ta haske ta shiga cikin aikace-aikacen motoci, likita da tsaro na masana'antu, ana ƙara jaddada ƙa'idodin cancanta, faɗaɗa kewayon yanayin aiki da binciken yanayin gazawa.

Ko da yake transistor ɗin haske mai rarrabuwa yana da mahimmanci a yawancin aikace-aikace saboda sauƙi da fa'idar farashi, waɗannan abubuwan suna nuni ga nan gaba inda za a sami mafi rikitarwa da mafita na musamman don aikace-aikace.