LTR-C951-TB IR Emitter and Detector Datasheet - 5mm Package - 30V Collector-Emitter - 940nm - English Technical Document

1. Product Overview

The LTR-C951-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 systems requiring reliable infrared detection. The primary function of this component is to convert incident infrared light into a corresponding electrical signal at its collector-emitter terminals. Its design is optimized for integration into automated assembly processes and standard surface-mount technology (SMT) lines.

The core advantage of this device lies in its use of a phototransistor structure, which provides internal gain, resulting in higher sensitivity compared to basic photodiodes. The integrated black epoxy dome lens helps in defining the viewing angle and can offer some degree of ambient light rejection, although the datasheet does not specify a dedicated filter for visible light noise reduction in this particular model. The component is specified as compliant with RoHS and Green Product initiatives.

The target market and applications are clearly oriented towards cost-effective, high-volume consumer and industrial electronics. Key application areas include infrared receivers for remote control systems and PCB-mounted infrared sensors for proximity sensing, object detection, and basic data transmission links where high-speed performance is not the primary requirement.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operating the device under conditions exceeding these values is not recommended.

• Power Dissipation (P_D): 100 mW. This is the maximum amount of power the device can dissipate as heat at an ambient temperature (T_A) of 25°C. 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 pins with the base open (phototransistor mode).
• Emitter-Collector Voltage (V_ECO): 5 V. The maximum reverse voltage applicable between emitter and collector.
• Operating Temperature Range (T_opr): -40°C to +85°C. The ambient temperature range over which the device is guaranteed to meet its published electrical specifications.
• Storage Temperature Range (T_stg): -55°C to +100°C. The temperature range for storing the device without applying power.
• Infrared Reflow Soldering Condition: Peak temperature of 260°C for a maximum of 10 seconds. This defines the thermal profile tolerance for SMT assembly.

2.2 Electrical & Optical Characteristics

These parameters are measured under specific test conditions at T_A=25°C and define the typical performance of the device.

• Collector-Emitter Breakdown Voltage (V_(BR)CEO): 30 V (Min). Confirms the Absolute Maximum Rating under a specific test condition (I_R = 100µA, no illumination).
• Emitter-Collector Breakdown Voltage (V_(BR)ECO): 5 V (Min). Confirms the reverse voltage rating.
• Collector-Emitter Saturation Voltage (V_CE(SAT)): 0.4 V (Max). When the phototransistor is fully "on" (saturated) under illumination (E_e=0.5 mW/cm² at 940nm) and with a collector current (I_C) of 100µA, the voltage drop between collector and emitter will be 0.4V or less. A lower V_CE(SAT) is generally better for switching applications.
• Rise Time (T_r) & Fall Time (T_f): 15 µs (Typ). These parameters specify the speed of the device. With a test condition of V_CE=5V, I_C=1mA, and R_L=1kΩ, the output takes approximately 15 microseconds to rise from 10% to 90% of its final value when illuminated, and another 15 µs to fall back when the light is removed. This indicates a device suited for low to moderate frequency applications (up to tens of kHz), not high-speed data transmission.
• Collector Dark Current (I_CEO): 100 nA (Max). This is the leakage current that flows through the collector-emitter junction when the device is in complete darkness (E_e = 0 mW/cm²) and with V_CE=20V. A lower dark current is desirable for better signal-to-noise ratio in low-light conditions.
• On-State Collector Current (I_C(ON)): 5.5 mA (Typ). This is the typical collector current generated when the device is illuminated with a specific irradiance of 0.5 mW/cm² of 940nm infrared light and biased with V_CE=5V. This parameter directly relates to the device's sensitivity.

3. Performance Curve Analysis

The datasheet references a section for "Typical Electrical / Optical Characteristics Curves." While the specific graphs are not provided in the text, we can infer their standard content and importance for design.

Typical curves for a phototransistor like the LTR-C951-TB would include:

• Collector Current (I_C) vs. Irradiance (E_e): This is the most crucial curve, showing the relationship between incident light power and output current for different collector-emitter voltages (V_CE). It demonstrates the linearity (or non-linearity) of the response and allows designers to calculate the necessary irradiance to achieve a desired output current.
• Collector Current (I_C) vs. Collector-Emitter Voltage (V_CE): These are output characteristic curves, plotted for different levels of irradiance. They show the operating regions (saturation and active) of the phototransistor and help in selecting the appropriate load resistor (R_L).
• Spectral Response: A curve showing the relative sensitivity of the device across different wavelengths of light. While the device is tested with 940nm light, this curve would show its response to other IR wavelengths (e.g., 850nm, 880nm) and potentially visible light, indicating the need for optical filtering if specific wavelength isolation is required.
• Temperature Dependence: Curves showing how key parameters like dark current (I_CEO) and sensitivity change over the operating temperature range. Dark current typically increases exponentially with temperature, which can be a critical factor in high-temperature or precision applications.

Designers must consult these graphs to accurately model the device's behavior in their specific circuit and environmental conditions, as the tabulated typical values only provide a snapshot at 25°C.

4. Mechanical & Package Information

4.1 Outline Dimensions

The device follows a standard package outline. The provided dimensional drawing (referenced in the datasheet) specifies the physical size, lead spacing, and lens geometry. Key features include a black epoxy body with a dome lens, which helps in controlling the directional response (viewing angle) of the sensor. The package is designed to be compatible with automatic pick-and-place equipment, facilitating high-volume manufacturing.

4.2 Polarity Identification

Phototransistors are polarized devices. The datasheet's outline drawing will clearly indicate the pinout: Collector (C) and Emitter (E). Incorrect polarity connection during PCB assembly will prevent the device from functioning.

4.3 Suggested Soldering Pad Layout & Package Dimensions

The datasheet includes a "Suggest Soldering Pad Dimensions" diagram. This is a critical reference for PCB layout designers. It provides the recommended copper pad geometry (size and shape) on the printed circuit board to ensure a reliable solder joint formation during reflow soldering while minimizing stress on the component. Adhering to these recommendations is essential for manufacturing yield and long-term reliability.

Furthermore, the "Package Dimensions Of Tape And Reel" section details how the components are supplied for automated assembly. It specifies the carrier tape dimensions, pocket spacing, reel diameter (7 inches), and orientation of the parts within the tape. This information is vital for programming the SMT placement machine correctly.

5. Assembly, Storage & Handling Guidelines

5.1 Soldering and Reflow Profile

The device is rated for infrared reflow soldering processes. The absolute maximum condition is a peak temperature of 260°C for a maximum of 10 seconds. The datasheet recommends following a JEDEC-standard reflow profile, which typically includes a pre-heat stage (150-200°C), a controlled ramp to peak temperature, and a controlled cooling phase. Adherence to the solder paste manufacturer's specifications is also emphasized. For manual repair, soldering iron temperature should not exceed 300°C, with a contact time of 3 seconds maximum per joint.

5.2 Storage Conditions

Moisture sensitivity is a critical factor for plastic SMD components. The LEDs/phototransistors are packaged in a moisture-proof bag with desiccant.

• Sealed Package: Should be stored at ≤30°C and ≤90% Relative Humidity (RH). The shelf life under these conditions is one year.
• Opened Package: Components exposed to ambient air should be stored at ≤30°C and ≤60% RH. It is strongly recommended to complete the IR reflow process within one week (168 hours) after opening the bag. For longer storage outside the original packaging, components must be stored in a sealed container with desiccant or in a nitrogen ambient. If stored for more than one week, a bake-out at 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent "popcorning" damage during reflow.

5.3 Cleaning

If post-solder cleaning is necessary, only alcohol-based solvents like isopropyl alcohol (IPA) should be used. Harsh or aggressive chemical cleaners may damage the epoxy lens or package.

6. Packaging and Ordering Information

The LTR-C951-TB is supplied in standard EIA packaging for automated assembly. The components are loaded into embossed carrier tape, which is then wound onto 7-inch diameter reels. Each reel contains 1500 pieces. The tape has a cover seal to protect components during handling and shipping. The datasheet notes compliance with the ANSI/EIA 481-1-A-1994 specification for tape and reel packaging.

7. Application Design Considerations

7.1 Typical Application Circuits

The datasheet provides a fundamental drive circuit recommendation. A phototransistor is a current-output device. In a typical switching application, it is connected in a common-emitter configuration:

• The collector is connected to the supply voltage (V_CC) through a load resistor (R_L).
• The emitter is connected to ground.
• The output signal is taken from the collector node.

When no light is incident, the phototransistor is off (high impedance), and the output voltage at the collector is pulled high to V_CC (minus a small dark current drop across R_L). When illuminated, the phototransistor turns on, current flows, and the output voltage drops to a low level (close to V_CE(SAT)). The value of R_L is chosen based on the desired output voltage swing, speed (as it forms an RC time constant with circuit parasitics), and the available photocurrent (I_C(ON)).

7.2 Design Notes and Cautions

• Ambient Light Immunity: The black lens provides some filtering, but for operation in environments with strong ambient IR (sunlight, incandescent bulbs), an additional external IR-pass/visible-block optical filter may be necessary to improve the signal-to-noise ratio.
• Speed Limitations: With rise/fall times in the tens of microseconds, this device is not suitable for high-speed data communication (e.g., IrDA). It is ideal for remote control codes (e.g., RC-5, NEC) and simple on/off detection.
• Biasing for Linear Operation: If used in a linear (analog) mode rather than as a switch, the device must be operated in its active region (V_CE > V_CE(SAT)). The non-linear characteristics shown in the I_C vs. E_e curves must be accounted for.
• Application Scope: The datasheet includes a standard caution that the component is intended for general-purpose electronics. Applications requiring exceptional reliability, especially in life-support, safety, or transportation systems, require prior consultation and likely component-level qualification.

8. Operating Principle

A phototransistor is a bipolar junction transistor (BJT) where the base region is exposed to light instead of being electrically contacted. The base-collector junction acts as a photodiode. When photons with sufficient energy (infrared, in this case) strike this junction, they generate electron-hole pairs. This photogenerated current acts as the base current (I_B) for the transistor. The transistor then amplifies this current by its DC current gain (h_FE), resulting in a much larger collector current (I_C = h_FE * I_B(photo)). This internal gain is what gives the phototransistor its high sensitivity compared to a simple photodiode, which has no internal amplification. The black epoxy package houses the semiconductor chip and forms the dome lens, which focuses incoming light onto the sensitive area.

9. FAQ Based on Technical Parameters

Q1: What is the typical viewing angle of this device?

A1: The datasheet does not specify a numerical viewing angle. The black dome lens typically provides a moderate viewing angle (e.g., ±20° to ±40° is common for such packages), but the exact value should be confirmed from the detailed outline drawing or by contacting the manufacturer.

Q2: Can I use this with an 850nm IR LED?

A2: The device is tested and its I_C(ON) specified at 940nm. Phototransistors generally have a broad spectral response in the near-infrared range. It will likely respond to 850nm light, but with potentially different sensitivity. For optimal performance and predictable signal levels, pairing it with an IR emitter at its peak sensitivity wavelength (likely around 940nm) is recommended. Consult the spectral response curve.

Q3: How do I choose the value of the load resistor (R_L)?

A3: R_L is chosen based on your supply voltage (V_CC), the desired output logic levels, and the required speed. For a 5V supply: To ensure a good logic 'low' (e.g., <0.8V) when the transistor is on, R_L ≤ (V_CC - V_CE(SAT)) / I_C(ON). With V_CC=5V, V_CE(SAT)=0.4V, I_C(ON)=5.5mA, R_L ≤ (5-0.4)/0.0055 ≈ 836Ω. A standard 1kΩ resistor is a common choice, providing a good compromise between current consumption and output swing. For faster speed, a smaller R_L is better (reduces RC time constant), but it increases power consumption.

Q4: Why is the dark current important?

A4: Dark current (I_CEO) sets the noise floor of the sensor. In a dark environment, this current still flows through R_L, creating a small voltage drop. This limits the minimum detectable light signal. In high-temperature applications, dark current increases significantly and can saturate the output, making the sensor unusable.