LTR-S971-TB IR Phototransistor Datasheet - Side View Package - Vce 30V - English Technical Documentation

1. Product Overview

The LTR-S971-TB is a discrete infrared (IR) phototransistor component designed for sensing applications. It belongs to a broad family of optoelectronic devices intended for use in environments requiring reliable detection of infrared light. The primary function of this component is to convert incident infrared radiation into an electrical signal, specifically a collector current proportional to the received IR power density.

Its core advantages include a side-viewing dome lens housed in a black package, which helps in directing the field of view and potentially reducing interference from ambient light from other angles. The device is packaged for modern assembly processes, being supplied on 8mm tape on 13-inch diameter reels, making it compatible with automatic placement equipment and infrared reflow soldering processes. It is also compliant with RoHS and green product standards.

The target markets and applications for this phototransistor are primarily in consumer electronics and industrial sensing. Key application areas include serving as an infrared receiver in systems like remote controls and enabling PCB-mounted infrared sensing for functions such as proximity detection, object sensing, and basic data transmission links where IR is the medium.

2. In-Depth Technical Parameter Analysis

The performance of the LTR-S971-TB is defined by a set of absolute maximum ratings and detailed electrical/optical characteristics, all specified at an ambient temperature (TA) of 25°C.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation.

• Power Dissipation (Pd): 100 mW. This is the maximum power the device can dissipate as heat.
• Collector-Emitter Voltage (V_CE): 30 V. The maximum voltage that can be applied between the collector and emitter terminals.
• Emitter-Collector Voltage (V_EC): 5 V. The maximum reverse voltage applicable between emitter and collector.
• Operating Temperature Range (T_op): -40°C to +85°C. The ambient temperature range for reliable device operation.
• Storage Temperature Range (T_stg): -55°C to +100°C. The temperature range for non-operational storage.
• Infrared Soldering Condition: Withstands 260°C for a maximum of 10 seconds, defining its reflow soldering capability.

2.2 Electrical & Optical Characteristics

These parameters define the device's performance under specified test conditions, representing typical operational behavior.

• Collector-Emitter Breakdown Voltage (V_(BR)CEO): 30 V (Min). Measured with a reverse leakage current (I_R) of 100µA and no incident IR illumination (E_e = 0 mW/cm²).
• Emitter-Collector Breakdown Voltage (V_(BR)ECO): 5 V (Min). Measured with I_E = 100µA and no illumination.
• Collector-Emitter Saturation Voltage (V_CE(SAT)): 0.4 V (Max). The voltage across the device when it is fully "on," tested at I_C = 100µA under an irradiance of 0.5 mW/cm².
• Rise Time (T_r) & Fall Time (T_f): 15 µs (Typ). These switching speed parameters are measured with V_CE=5V, I_C=1mA, and R_L=1kΩ, indicating its suitability for moderate-speed detection.
• Collector Dark Current (I_CEO): 100 nA (Max). The leakage current flowing from collector to emitter when no light is present, at V_CE=20V. A lower value is better for signal-to-noise ratio.
• On-State Collector Current (I_C(ON)): 4.0 mA (Typ). The output current when the device is illuminated, tested at V_CE=5V under an irradiance of 0.5 mW/cm² from a 940nm source. This is a key sensitivity parameter.

3. Performance Curve Analysis

The datasheet references a section for typical electrical/optical characteristic curves. These graphical representations are crucial for design engineers to understand device behavior beyond single-point specifications.

While the specific curves are not detailed in the provided text, typical plots for a phototransistor like the LTR-S971-TB would include:

• Collector Current (I_C) vs. Collector-Emitter Voltage (V_CE): A family of curves parameterized by different levels of incident infrared irradiance (E_e). This shows the output characteristics and the saturation region.
• Collector Current (I_C) vs. Incident Irradiance (E_e): This plot, often at a fixed V_CE, demonstrates the linearity (or non-linearity) of the phototransistor's response to light intensity, which is central to its sensitivity.
• Spectral Response: A curve showing the relative sensitivity of the device across different wavelengths of light. While the test condition specifies 940nm, this curve would show the peak response wavelength and the bandwidth of sensitivity, important for filtering out unwanted light sources.
• Temperature Dependence: Graphs showing how key parameters like dark current (I_CEO) and collector current (I_C) vary with ambient temperature, which is critical for designs operating outside room temperature.

4. Mechanical & Packaging Information

4.1 Outline Dimensions

The device features a side-view package with a dome lens. All dimensions are provided in millimeters with a standard tolerance of ±0.1 mm unless otherwise specified. The exact mechanical drawing defines the body size, lead spacing, lens position, and overall footprint critical for PCB layout.

4.2 Suggested Soldering Pad Dimensions

A recommended land pattern (footprint) for the PCB is provided. Adhering to these dimensions ensures proper solder joint formation, mechanical stability, and thermal relief during the soldering process.

4.3 Package Dimensions of Tape and Reel

Detailed drawings specify the carrier tape dimensions (pocket size, pitch), cover tape, and reel dimensions. This information is essential for automated assembly line setup. Key specifications noted are a 13-inch reel containing 9000 pieces, with a maximum of two consecutive missing components allowed, following ANSI/EIA 481-1-A-1994 standards.

5. Soldering & Assembly Guidelines

5.1 Storage Conditions

The device is moisture-sensitive. In its sealed moisture-proof bag with desiccant, it should be stored at ≤30°C and ≤90% RH and used within one year. Once opened, the storage environment must not exceed 30°C and 60% RH. Components out of their original packaging for more than one week should be baked at approximately 60°C for at least 20 hours before soldering to prevent "popcorning" during reflow.

5.2 Soldering Parameters

Reflow Soldering: A JEDEC-compliant profile is recommended.

• Pre-heat: 150–200°C for a maximum of 120 seconds.
• Peak Temperature: Maximum of 260°C.
• Time above 260°C: Maximum of 10 seconds, with a maximum of two reflow cycles allowed.

Hand Soldering (Soldering Iron):

• Iron Temperature: Maximum of 300°C.
• Contact Time: Maximum of 3 seconds per joint.

The datasheet emphasizes that the optimal profile depends on the specific PCB design, components, and solder paste used.

5.3 Cleaning

If cleaning is necessary after soldering, only alcohol-based solvents like isopropyl alcohol should be used.

6. Application Notes & Design Considerations

6.1 Drive Circuit Design

A phototransistor is fundamentally a current-output device. The datasheet provides crucial guidance for driving multiple devices. Circuit Model (A) is the recommended configuration, where each phototransistor has its own series current-limiting resistor connected to the supply voltage. This ensures intensity uniformity by compensating for minor variations in the current-voltage (I-V) characteristics between individual devices. Circuit Model (B), where multiple devices share a single resistor, is discouraged as it can lead to uneven brightness or current sharing due to device mismatches.

6.2 Application Scope and Cautions

The component is intended for standard electronic equipment (office, communications, household). The datasheet includes a specific caution against using it in safety-critical or high-reliability applications—such as aviation, medical life-support, or transportation control systems—without prior consultation and qualification, as failure could jeopardize life or health.

6.3 Typical Application Scenarios

• Infrared Remote Control Receivers: Detecting modulated IR signals from remotes.
• Proximity and Object Detection: Sensing the presence or absence of an object by detecting reflected or blocked IR light.
• Basic IR Data Links: For short-range, low-speed wireless data transmission.
• Security Alarm Sensors: As part of a beam-break or reflection-based intrusion detection system.

7. Operating Principle

A phototransistor operates on the principle of the photoelectric effect within a bipolar junction transistor (BJT) structure. Incident photons with sufficient energy (in the infrared spectrum for this device) are absorbed in the base-collector junction region, generating electron-hole pairs. These photogenerated carriers are effectively amplified by the transistor's current gain (beta, β). The base terminal is often left unconnected or is used with a resistor for bias control. The resulting output is a collector current (I_C) that is much larger than the primary photocurrent, providing inherent signal amplification. The side-view lens focuses and directs incoming IR light onto the sensitive semiconductor area, defining the device's field of view.

8. Packaging and Ordering Information

The standard packaging is 9000 pieces per 13-inch reel. The tape and reel specifications comply with ANSI/EIA standards to ensure compatibility with automated pick-and-place machinery. The part number LTR-S971-TB uniquely identifies this specific variant (likely indicating package type 'TB' for side-view).

9. FAQs Based on Technical Parameters

Q: What is the typical response speed of this sensor?
A: The typical rise and fall times are 15 microseconds, making it suitable for detecting modulated IR signals common in remote controls, which typically operate at carrier frequencies like 38 kHz.

Q: How sensitive is the LTR-S971-TB?
A: Under a test condition of 0.5 mW/cm² at 940nm and V_CE=5V, it typically provides 4.0 mA of collector current. The lower the irradiance needed to produce a usable output current, the higher the sensitivity.

Q: Can I use it outdoors or in high-temperature environments?
A: Its operating temperature range is -40°C to +85°C, allowing for use in a wide range of environments. However, designers must consider the temperature dependence of its dark current and output current, which can affect signal-to-noise ratio at extremes.

Q: Why is a separate resistor needed for each phototransistor in parallel?
A: Due to natural manufacturing variations, the I-V characteristics of individual phototransistors differ slightly. A shared resistor forces them to have the same voltage, which can cause significant current imbalance. Individual resistors allow each device to self-bias, ensuring more uniform current sharing and performance.

10. Design and Usage Case Example

Scenario: Designing a simple object counter using an IR break-beam sensor.

1. Setup: An IR emitter (IRED) is placed on one side of a conveyor belt, and the LTR-S971-TB phototransistor is placed directly opposite.
2. Circuit: The phototransistor is configured in a common-emitter setup. A pull-up resistor (e.g., 1kΩ to 10kΩ) is connected from the collector to V_CC (e.g., 5V). The emitter is connected to ground. The output signal is taken from the collector node.
3. Operation: When the IR beam is uninterrupted, the phototransistor is illuminated, causing it to conduct and pull the collector voltage low (near V_CE(SAT)). When an object breaks the beam, the illumination ceases, the phototransistor turns off, and the collector voltage is pulled high by the resistor.
4. Signal Processing: This digital voltage transition (low-to-high) can be fed into a microcontroller's digital input pin or a comparator to trigger a counting routine.
5. Design Considerations: The value of the pull-up resistor affects the switching speed and current consumption. Ambient IR light (e.g., from sunlight) can cause false triggers, so the system may require optical filtering, housing to shield ambient light, or modulation/demodulation of the IR beam.

Note: Product appearance and specifications are subject to change without notice for improvement.