LTR-C971-TB Infrared Phototransistor Datasheet - Side View Package - Vce 30V - English Technical Documentation

1. Product Overview

The LTR-C971-TB is a discrete infrared phototransistor component designed for sensing applications. It is part of a broad product line aimed at providing solutions for infrared detection, featuring characteristics suitable for reliable performance in various electronic systems. The device is engineered to meet industry standards for automatic placement and soldering processes.

1.1 Features

• Compliant with RoHS and Green Product standards.
• Features a black dome lens with a side view configuration.
• Packaged in 12mm tape on 7-inch diameter reels for automated handling.
• Compatible with automatic placement equipment.
• Compatible with infrared reflow soldering processes.
• Conforms to EIA standard package specifications.

1.2 Applications

• Infrared receiver modules.
• PCB-mounted infrared sensors.

2. Outline Dimensions

The mechanical outline and dimensions of the LTR-C971-TB phototransistor are provided in the datasheet drawings. All dimensions are specified in millimeters, with a standard tolerance of ±0.1mm unless otherwise noted. It is important to refer to the detailed dimensional drawings for accurate PCB footprint design. Specifications are subject to change without notice.

3. Absolute Maximum Ratings

The following table lists the absolute maximum ratings for the LTR-C971-TB phototransistor at an ambient temperature (TA) of 25°C. Exceeding these limits may cause permanent damage to the device.

A suggested infrared reflow profile for lead-free processes is also included in the datasheet for reference during assembly.

4. Electrical and Optical Characteristics

The key electrical and optical parameters are defined at TA=25°C. These characteristics are crucial for circuit design and performance prediction.

Note: The test tolerance for IC(ON) is ±15%.

5. Typical Performance Curves

The datasheet includes a set of typical characteristic curves measured at 25°C ambient temperature (unless otherwise noted). These graphs visually represent the relationship between key parameters such as collector current versus irradiance, response time under different loads, and the temperature dependence of dark current. Analyzing these curves helps engineers understand the device's behavior under non-standard or varying operating conditions, which is essential for robust system design.

6. Soldering Pad Layout and Recommendations

Recommended solder pad dimensions for PCB layout are provided to ensure proper soldering and mechanical stability. The datasheet suggests using a metal stencil for solder paste printing with a thickness of 0.1mm (4 mils) or 0.12mm (5 mils). Adhering to these pad dimensions and stencil specifications is critical for achieving reliable solder joints during the reflow process and preventing issues like tombstoning or insufficient solder.

7. Tape and Reel Packaging Specifications

The LTR-C971-TB is supplied in a tape and reel format suitable for high-volume, automated assembly lines. Detailed package dimensions for both the carrier tape and the reel are specified. Key notes include: all dimensions are in millimeters, empty component pockets are sealed with top cover tape, each 13-inch reel contains 6000 pieces, a maximum of two consecutive missing components is allowed, and the packaging conforms to ANSI/EIA 481-1-A-1994 specifications.

8. Important Cautions and Handling Guidelines

8.1 Intended Application

This component is designed for use in ordinary electronic equipment, including office equipment, communication devices, and household applications. It is not intended for safety-critical systems where failure could jeopardize life or health (e.g., aviation, medical devices). For such applications, consultation with the component supplier is required prior to design.

8.2 Storage Conditions

Proper storage is essential to maintain component reliability. For sealed moisture-proof bags with desiccant, store at ≤30°C and ≤90% RH, with a recommended use-within period of one year. Once the original packaging is opened, components should be stored at ≤30°C and ≤60% RH. It is advised to complete IR reflow soldering within one week after opening. For longer storage outside the original bag, use a sealed container with desiccant or a nitrogen desiccator. Components stored unpackaged for over one week should be baked at approximately 60°C for at least 20 hours before soldering.

8.3 Cleaning

If cleaning is necessary, use alcohol-based solvents such as isopropyl alcohol. Avoid using aggressive or unknown chemical cleaners that may damage the package or lens.

8.4 Soldering Process

Detailed soldering recommendations are provided to ensure assembly reliability.

• Reflow Soldering: Pre-heat to 150–200°C for a maximum of 120 seconds. The peak temperature should not exceed 260°C, and the time above this temperature should be limited to 10 seconds maximum. Reflow should be performed a maximum of two times.
• Soldering Iron: The iron tip temperature should not exceed 300°C, and soldering time per lead should be limited to 3 seconds maximum for a single operation.

The datasheet emphasizes that the optimal temperature profile depends on the specific board design, components, solder paste, and oven. It recommends using the provided JEDEC-compliant profile as a generic target and adhering to limits from both JEDEC and the solder paste manufacturer.

8.5 Drive Circuit Recommendation

For applications involving multiple devices, a series current-limiting resistor is strongly recommended for each phototransistor in the circuit. This practice, illustrated as "Circuit Model (A)" in the datasheet, helps ensure current uniformity and consistent performance across all devices. The alternative parallel connection without individual resistors ("Circuit Model (B)") may lead to brightness or sensitivity variations due to differences in the individual devices' current-voltage (I-V) characteristics.

9. Product Information and Revisions

The manufacturer reserves the right to modify the product's appearance and specifications for improvement without prior notice. Designers should always refer to the latest version of the datasheet for the most current information.

10. Technical Deep Dive and Design Considerations

10.1 Principle of Operation

An infrared phototransistor operates by converting incident infrared light into an electrical current. It is essentially a bipolar junction transistor where the base current is generated by photons striking the base-collector junction (which acts as a photodiode). When infrared light of sufficient wavelength (typically 940nm for this device) illuminates the active area, electron-hole pairs are generated. This photocurrent is then amplified by the transistor's gain, resulting in a much larger collector current that can be easily measured by external circuitry. The side-view package with a black dome lens helps define a specific field of view and can offer some rejection of ambient visible light.

10.2 Key Parameter Analysis

• Sensitivity (IC(ON)): The typical on-state collector current of 4.0 mA under 0.5 mW/cm² irradiance at 940nm indicates the device's sensitivity. Designers must ensure the incident IR signal strength meets or exceeds this irradiance level for reliable switching or analog detection.
• Speed (Tr, Tf): The 15 μs typical rise and fall times define the device's switching speed. This parameter is critical for data transmission applications (like IR remote controls) where a high bit rate is required. The specified test condition (VCE=5V, IC=1mA, RL=1KΩ) provides a standard benchmark.
• Dark Current (ICEO): The maximum dark current of 100 nA at VCE=20V represents the leakage current when no light is present. A low dark current is essential for achieving a high signal-to-noise ratio, especially in low-light detection scenarios or when using high-value load resistors for increased voltage gain.
• Voltage Ratings (V(BR)CEO, V(BR)ECO): The 30V collector-emitter and 5V emitter-collector breakdown voltages define the safe operating area for the applied bias. Circuit designs must ensure these limits are not exceeded, even under transient conditions.

10.3 Application Circuit Design

The most common configuration is to use the phototransistor in a common-emitter switch mode. The collector is connected to the supply voltage (VCC) through a load resistor (RL), and the emitter is grounded. The output signal is taken from the collector node. The value of RL is a key design choice: a larger RL provides higher output voltage swing for a given photocurrent (higher gain) but slows down the response time due to increased RC time constant. The datasheet's speed specifications are given with RL=1KΩ, providing a reference point. For analog applications requiring linear response, the device should be operated in the photodiode mode (base left open, using only the collector-base junction) or with careful biasing to avoid saturation.

10.4 Environmental and Assembly Considerations

The operating temperature range of -40°C to +85°C makes the device suitable for consumer, industrial, and some automotive environments. Designers should consider the temperature coefficient of the dark current and sensitivity, which typically increase and decrease with temperature, respectively. The strict soldering profile guidelines are necessary because the plastic package and internal wire bonds are sensitive to thermal shock and excessive heat. Following the JEDEC-based profile minimizes stress and prevents latent failures.

10.5 Comparison and Selection

When selecting an infrared sensor, engineers compare phototransistors with photodiodes. Phototransistors offer higher gain (output current per unit of light) but are generally slower and have a more nonlinear response compared to photodiodes. The LTR-C971-TB, with its integrated amplification, is an excellent choice for simple digital detection (presence/absence of an IR signal) or low-speed analog sensing where high output is needed without additional amplifier stages. For high-speed data links or precise analog light measurement, a PIN photodiode might be more appropriate.

10.6 Practical Use Case Example

A typical use case is in an infrared proximity sensor for a touchless faucet. An infrared LED emitter pulses at 940nm. The LTR-C971-TB phototransistor, placed nearby, detects the reflected signal. When a hand is placed under the faucet, it reflects the IR light back to the sensor, causing the collector current to increase. This change is detected by a microcontroller, which then activates the water valve. The side-view package allows for a compact sensor module where the LED and phototransistor are mounted on the same PCB plane. The device's sensitivity ensures reliable detection even with weak reflections, and its speed is more than adequate for this slow human-motion interface. The design would include the recommended series resistor for the driving LED and a suitable load resistor (e.g., 10kΩ) on the phototransistor's collector to translate the current change into a measurable voltage for the microcontroller's ADC or comparator input.

10.7 Industry Trends

The trend in discrete infrared components is towards higher integration, smaller packages, and improved performance. While devices like the LTR-C971-TB remain vital for cost-sensitive or space-constrained designs, there is growing adoption of integrated solutions that combine the photodetector, amplifier, and digital logic (like I²C output) in a single package. These modules simplify design but may come at a higher cost. Another trend is the increased use of specific wavelength filters integrated into the package to improve immunity to ambient light noise, a feature mentioned as available in the broader product line. For basic detection tasks, the discrete phototransistor offers an optimal balance of performance, cost, and design flexibility.