LTR-C950-TB-T IR Phototransistor Datasheet - Side View Package - Vce 30V - English Technical Documentation

1. Product Overview

The LTR-C950-TB-T is a discrete infrared (IR) phototransistor component designed for sensing applications. It belongs to a broad family of optoelectronic devices intended for use in systems requiring reliable detection of infrared light. The primary function of this component is to convert incident infrared radiation into a corresponding electrical current at its collector terminal. Its side-view, dome lens package with a black housing is optimized for PCB mounting and helps in managing ambient light interference.

The device is engineered for compatibility with modern automated assembly processes, including placement equipment and infrared reflow soldering. It is characterized by its responsiveness to 940nm wavelength infrared light, which is commonly used in various remote control and sensing systems to avoid visible light noise.

1.1 Core Features and Advantages

• RoHS Compliant & Green Product: Manufactured without hazardous substances, adhering to environmental standards.
• Optical Design: Features a black, side-view dome lens that provides a specific field of view and helps shield the sensor from unwanted ambient light.
• Manufacturing Compatibility: Supplied in 8mm tape on 7-inch diameter reels, making it fully compatible with high-speed automatic placement (pick-and-place) machines.
• Process Compatibility: Rated to withstand standard infrared reflow soldering profiles used in surface-mount technology (SMT) assembly lines.
• Standardized Package: Conforms to EIA standard package outlines, ensuring predictability in PCB footprint design.

1.2 Target Applications

This phototransistor is suitable for a range of electronic applications where non-contact detection or sensing is required. Typical use cases include:

• Infrared Receivers: Decoding signals from remote controls in consumer electronics (TVs, audio systems, set-top boxes).
• PCB-Mounted Proximity/Object Sensors: Detecting the presence, absence, or position of an object in appliances, automation equipment, and security devices.
• Basic Optical Switching: Used in slot-type interrupters or reflective sensors.

2. In-Depth Technical Parameter Analysis

The following sections provide a detailed breakdown of the device's operational limits and performance characteristics under specified test conditions.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed.

• Power Dissipation (P_D): 100 mW. The maximum continuous power the device can dissipate as heat.
• Collector-Emitter Voltage (V_CEO): 30 V. The maximum voltage that can be applied between the collector and emitter terminals.
• Emitter-Collector Voltage (V_ECO): 5 V. The maximum reverse voltage between emitter and collector.
• Operating Temperature Range (T_A): -40°C to +85°C. The ambient temperature range for normal functional operation.
• Storage Temperature Range (T_stg): -55°C to +100°C. The safe temperature range for the device when not powered.
• Infrared Soldering Condition: Withstands a peak temperature of 260°C for a maximum of 10 seconds during reflow.

2.2 Electrical & Optical Characteristics

These parameters are measured at an ambient temperature (T_A) of 25°C and define the typical performance of the device.

• Collector-Emitter Breakdown Voltage (V_(BR)CEO): 30 V (Min). The voltage at which a specified small reverse current (I_R = 100µA) flows with no illumination (E_e = 0 mW/cm²).
• Emitter-Collector Breakdown Voltage (V_(BR)ECO): 5 V (Min). Similar to V_(BR)CEO but for the reverse bias condition.
• Collector-Emitter Saturation Voltage (V_CE(SAT)): 0.4 V (Max). The voltage across the collector and emitter when the transistor is fully "on" (conducting) under an irradiance of 0.5 mW/cm² and a collector current (I_C) of 100µA. A lower value indicates better performance.
• Rise Time (T_r) & Fall Time (T_f): 15 µs (Typ). The time required for the output current to rise from 10% to 90% (rise time) or fall from 90% to 10% (fall time) of its maximum value in response to a pulsed light input. Measured with V_CE=5V, I_C=1mA, and R_L=1kΩ.
• Collector Dark Current (I_CEO): 100 nA (Max). The small leakage current that flows from collector to emitter when no light is incident on the device (V_CE = 20V). Lower is better for sensitivity.
• On-State Collector Current (I_C(ON)): 1.5 to 9.2 mA. The collector current generated when the device is illuminated with a standardized infrared source (E_e=0.5 mW/cm², λ=940nm, V_CE=5V). This is the key sensitivity parameter.

3. Binning System Explanation

The devices are sorted into performance bins based on their On-State Collector Current (I_C(ON)). This allows designers to select components with consistent sensitivity for their specific circuit requirements.

• BIN A: I_C(ON) range from 1.5 mA (Min) to 2.9 mA (Max).
• BIN B: I_C(ON) range from 2.9 mA (Min) to 5.5 mA (Max).
• BIN C: I_C(ON) range from 5.5 mA (Min) to 9.2 mA (Max).

A tolerance of ±15% is applied to the limits of each bin. Designers must account for this variation when calculating circuit gain and threshold levels.

4. Performance Curve Analysis

The datasheet provides several characteristic graphs that illustrate device behavior under varying conditions.

4.1 Spectral Sensitivity

A graph (Fig.1) shows the relative spectral sensitivity versus wavelength. The LTR-C950-TB-T exhibits peak sensitivity around 940nm, which matches common infrared emitters (IREDs). Sensitivity drops sharply for wavelengths shorter than 800nm and longer than 1100nm, providing inherent filtering against much of the visible light spectrum.

4.2 Collector Dark Current vs. Temperature

The curve (Fig.3) plots Collector Dark Current (I_CEO) against Ambient Temperature (T_A). I_CEO increases exponentially with temperature. This is a critical consideration for high-temperature applications, as increased dark current raises the noise floor and can affect the signal-to-noise ratio of the sensor.

4.3 Dynamic Response vs. Load

Graphs (Fig.4) show how Rise Time (T_r) and Fall Time (T_f) vary with Load Resistance (R_L). Both times increase with higher load resistance. For applications requiring fast switching, a smaller load resistor is beneficial, though it will reduce the output voltage swing.

4.4 Relative Collector Current vs. Irradiance

This graph (Fig.5) demonstrates the relationship between output current and incident light power (irradiance). The response is generally linear over a significant range, which is desirable for analog sensing applications. It confirms the device's function as a proportional light-to-current converter.

4.5 Radiation Pattern

A polar diagram (Fig.6) illustrates the angular sensitivity of the side-view package. The relative radiant intensity (or sensitivity) is plotted against the angle of incident light. This diagram is essential for mechanical design, showing the effective field of view (FOV) within which the sensor will reliably detect an IR source.

5. Mechanical & Package Information

5.1 Outline Dimensions

The device has a standard side-view phototransistor package. Key dimensions include body size, lead spacing, and lens position. All dimensions are provided in millimeters with a typical tolerance of ±0.1mm unless otherwise specified. The pinout identifies the Collector and Emitter terminals.

5.2 Recommended Solder Pad Design

A land pattern (footprint) for PCB design is provided. The recommended pad dimensions are 1.0mm x 1.8mm for the mounting pads, with a 1.8mm gap between them. Following this pattern ensures a reliable solder joint during reflow and proper mechanical alignment.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested reflow profile for lead-free (Pb-free) processes is included. Key parameters are:

• Pre-heat: 150-200°C for up to 120 seconds maximum.
• Peak Temperature: 260°C maximum.
• Time Above Liquidus: The device should not be exposed to temperatures above 260°C for more than 10 seconds.

The profile is based on JEDEC standards. Engineers must characterize the profile for their specific PCB design, solder paste, and oven.

6.2 Hand Soldering

If hand soldering is necessary, use a soldering iron with a temperature not exceeding 300°C, and limit the contact time to 3 seconds per joint. Avoid applying stress to the component leads.

6.3 Cleaning

If post-solder cleaning is required, use only alcohol-based solvents such as isopropyl alcohol. Avoid aggressive or unknown chemical cleaners that may damage the plastic package or lens.

7. Packaging and Handling

7.1 Tape and Reel Specifications

The components are packaged in 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels. Each reel contains 2000 pieces. The packaging conforms to ANSI/EIA 481-1-A-1994 standards. Notes specify that a maximum of two consecutive component pockets may be empty (as per tape sealing) and that the orientation of the parts within the tape is marked.

7.2 Storage Conditions

Sealed Package: Store at ≤30°C and ≤90% Relative Humidity (RH). The shelf life in the sealed moisture barrier bag (with desiccant) is one year.
Opened Package: For components removed from the sealed bag, the storage environment must not exceed 30°C / 60% RH. It is strongly recommended to complete IR reflow soldering within one week of opening. For longer storage outside the original bag, store in a sealed container with desiccant or in a nitrogen desiccator. Components stored open for more than one week should be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

8. Application Notes & Design Considerations

8.1 Drive Circuit Design

The phototransistor is a current-output device. In a typical circuit, it is connected in a common-emitter configuration. A load resistor (R_L) is placed between the collector and the supply voltage (V_CC). The emitter is connected to ground. Incident light causes collector current (I_C) to flow, creating a voltage drop across R_L. This voltage (V_OUT = V_CC - I_C*R_L) is the signal output.

Key Design Choices:

• Load Resistor (R_L): A higher R_L gives a larger output voltage swing for a given light change but increases response time (see Fig.4). A lower R_L provides faster response but a smaller signal.
• Biasing: The device requires no external bias current for the base; it is entirely controlled by light.
• Multiple Devices: If multiple phototransistors need to be connected in parallel in an application, it is not recommended to connect them directly together. Variations in their I_C(ON) (even within a bin) will cause uneven current sharing. A current-limiting resistor should be placed in series with each device to ensure uniform behavior.

8.2 Improving Signal-to-Noise Ratio (SNR)

• Modulation: For remote control applications, the IR source (IRED) is pulsed at a specific carrier frequency (e.g., 38kHz). The receiving circuit includes a bandpass filter tuned to this frequency, which rejects constant ambient light and noise.
• Optical Filtering: The black package and the natural spectral sensitivity (peak at 940nm) provide some filtering against visible light. For extremely noisy environments, an additional external IR-pass/visible-block filter can be used over the sensor.
• Electrical Filtering: Following the phototransistor with an amplifier stage that includes high-pass or band-pass filtering can further improve SNR for AC-coupled signals.

8.3 Layout Considerations

• Place the sensor away from heat-generating components to minimize temperature-induced drift in dark current.
• Ensure the recommended solder pad geometry is used to prevent tombstoning or misalignment during reflow.
• Consider the radiation pattern (Fig.6) when designing the mechanical housing to ensure the IR source falls within the sensor's sensitive viewing angle.

9. Operational Principle

A phototransistor is fundamentally a bipolar junction transistor (BJT) where the base current is generated by light instead of an electrical connection. The base-collector junction acts as a photodiode. When photons with sufficient energy (infrared, in this case) strike this junction, they create electron-hole pairs. This photogenerated current is then amplified by the transistor's current gain (β or h_FE), resulting in a much larger collector current that is proportional to the incident light intensity. The side-view package positions the sensitive semiconductor chip such that it can detect light arriving parallel to the PCB surface.

10. Practical Design Example

Scenario: Object Detection in a Vending Machine. A beam-breaking sensor is needed to detect when a product passes through a chute.

1. Component Selection: An LTR-C950-TB-T (BIN B) is chosen for its side-view package, suitable for mounting on the edge of a PCB facing across the chute. A matching 940nm IRED is selected as the light source.
2. Circuit Design: The phototransistor is configured in a common-emitter circuit with V_CC = 5V. A load resistor R_L = 2.2kΩ is chosen as a compromise between good voltage swing and acceptable speed for this application. The output is fed to a comparator with a threshold set to differentiate between "beam present" (high output) and "beam blocked" (low output).
3. Mechanical Integration: The IRED and phototransistor are mounted on opposite sides of the product chute, aligned according to their radiation/sensitivity patterns. Light baffles may be added to limit stray light.
4. Considerations: The ambient temperature inside the machine is monitored to ensure it stays within the operating range. The initial output voltage is measured and the comparator threshold is set with margin to account for component tolerance (bin ±15%) and potential dust accumulation on the lenses over time.