LTR-C155DD-G Photodiode Datasheet - 940nm Peak Wavelength - 5V Reverse Voltage - English Technical Document

1. Product Overview

The LTR-C155DD-G is a discrete infrared photodiode component designed for sensing applications in the near-infrared spectrum. It is part of a broad family of optoelectronic devices intended for use in systems requiring reliable detection of infrared signals. Its primary function is to convert incident infrared light into an electrical current, enabling its use as a receiver or sensor element.

1.1 Core Advantages and Target Market

This component offers several key advantages for designers. It features a high signal-to-noise ratio, which is critical for distinguishing valid infrared commands from ambient light noise in environments like living rooms or offices. The device is compatible with automatic placement equipment and infrared reflow soldering processes, making it suitable for high-volume, automated manufacturing lines. Its primary target markets include consumer electronics for remote control systems, security and alarm systems for motion or beam detection, and various applications involving short-range infrared data transmission.

1.2 Features

• Compliant with RoHS and Green Product directives.
• Features a top view package with a water-clear flat lens for consistent angular response.
• Supplied in 8mm tape on 7-inch diameter reels for automated assembly.
• Compatible with automatic placement (pick-and-place) equipment.
• Withstands standard infrared reflow soldering processes.
• Packaged in an EIA standard form factor.

1.3 Applications

• Infrared receiver modules for remote controls (TV, AC, set-top boxes).
• PCB-mounted infrared sensors for proximity sensing or object detection.
• Security alarm systems using infrared beams.
• Simple infrared wireless data transmission links.

2. Technical Parameters: In-Depth Objective Interpretation

The electrical and optical characteristics define the operational boundaries and performance of the photodiode. Understanding these parameters is essential for proper circuit design and ensuring reliable operation within the intended application.

2.1 Absolute Maximum Ratings

These ratings specify the limits beyond which permanent damage to the device may occur. They are not for continuous operation.

• Power Dissipation (Pd): 150 mW maximum. This is the total power the device can dissipate as heat, primarily from the reverse bias current and any photocurrent under high illumination.
• Reverse Voltage (VR): 30 V maximum. Applying a voltage higher than this in the reverse direction may cause breakdown and damage the photodiode junction.
• Operating Temperature Range (TA): -40°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range (Tstg): -55°C to +100°C. The device can be stored without operation within these limits.
• Infrared Soldering Condition: Withstands 260°C peak temperature for 10 seconds, which aligns with typical lead-free (Pb-free) reflow profiles.

2.2 Electrical & Optical Characteristics (TA=25°C)

These are the typical and guaranteed performance parameters under specified test conditions.

• Forward Voltage (Vf): 0.4V to 1.0V at If=1mA. This parameter is relevant if the photodiode is inadvertently forward-biased; it is not its normal operating mode.
• Reverse Breakdown Voltage V(BR): 30V minimum at IR=100µA. This confirms the device can safely handle the maximum rated reverse voltage.
• Reverse Dark Current (ID): 100 nA maximum at VR=5V, Ee=0mW/cm². This is the leakage current when no light is present. A lower dark current improves sensitivity to weak signals.
• Open Circuit Voltage (VOC): 0.4V maximum at λ=940nm, Ee=0.5mW/cm². This is the voltage generated by the photodiode in photovoltaic mode (no external bias) under illumination.
• Rise Time (Tr) & Fall Time (Tf): 0.30µs and 0.28µs typical, respectively, at VR=10V, RL=1kΩ. These parameters define the switching speed, making the device suitable for decoding modulated infrared signals (e.g., from remote controls operating at 38-40 kHz).
• Reverse Light Current (Ip): 16 µA typical (10 µA min) at VR=5V, λ=940nm, Ee=1mW/cm². This is the photocurrent generated when the diode is reverse-biased, which is the standard operating mode for linear response and speed.
• Short Circuit Current (Is): 16 µA typical under the same conditions as Ip. In photovoltaic mode, this is the maximum current the device can deliver.
• Total Capacitance (CT): 14 pF typical at VR=3V, f=1MHz. This junction capacitance affects the high-frequency response; a lower capacitance allows for higher bandwidth.
• Peak Sensing Wavelength (λp): 910 nm typical. The photodiode is most sensitive to infrared light at this wavelength, making it ideal for pairing with 940nm infrared emitting diodes (IREDs).

3. Performance Curve Analysis

The provided graphs offer visual insights into the device's behavior under varying conditions.

3.1 Photocurrent vs. Irradiance

The curve shows the relationship between incident light power (irradiance Ee) and the generated photocurrent (Ip). For a photodiode operating in the linear region (reverse-biased), this relationship is typically linear. The graph confirms that at 1 mW/cm² of 940nm light, the photocurrent is approximately 16 µA, as stated in the table. This linearity is crucial for analog sensing applications.

3.2 Spectral Sensitivity

This graph plots the relative radiant sensitivity against wavelength. It shows a peak around 910nm and a significant response in the range of approximately 800nm to 1050nm. The sensitivity drops sharply for visible light (below 700nm), which is beneficial for rejecting ambient light noise from sources like incandescent bulbs or sunlight. The inclusion of a filter, as mentioned in the description, would further sharpen this cutoff.

3.3 Total Power Dissipation vs. Ambient Temperature

This derating curve illustrates how the maximum allowable power dissipation decreases as the ambient temperature increases. At 25°C, the full 150 mW is permissible. As temperature rises towards the maximum operating limit of 85°C, the allowable power dissipation decreases linearly. This is critical for thermal management in the application design to prevent overheating.

3.4 Angular Sensitivity Diagram

The polar diagram depicts the relative sensitivity at different angles of incident light. A photodiode with a flat lens, like this one, typically has a relatively wide viewing angle (often around ±60 degrees where sensitivity falls to 50%). This wide angle is advantageous for receivers that need to capture signals from a broad area without precise alignment.

4. Mechanical and Packaging Information

4.1 Outline Dimensions

The device conforms to a standard industry package outline. Key dimensions include the body size, lead spacing, and overall height. The package is designed for surface-mount technology (SMT). All dimensions are in millimeters with a standard tolerance of ±0.1mm unless otherwise specified.

4.2 Polarity Identification and Pad Design

The cathode is typically marked on the package. The datasheet provides suggested soldering pad dimensions for PCB layout. A recommended pad design ensures a reliable solder joint and proper mechanical stability during and after the reflow process. It is advised to use a metal stencil with a thickness of 0.1mm to 0.12mm for solder paste application.

5. Soldering and Assembly Guidelines

5.1 Reflow Soldering Profile

The component is qualified for lead-free (Pb-free) reflow soldering processes. A suggested temperature profile is provided, adhering to JEDEC standards. Key parameters include a pre-heat zone (150-200°C), a peak temperature not exceeding 260°C, and a time above liquidus (TAL) that ensures proper solder joint formation without exposing the component to excessive thermal stress. The device can withstand this profile for a maximum of 10 seconds at peak temperature, up to two times.

5.2 Hand Soldering

If hand soldering is necessary, it should be performed with a soldering iron tip temperature not exceeding 300°C, and the contact time should be limited to a maximum of 3 seconds per joint. This minimizes the risk of thermal damage to the semiconductor die or the plastic package.

5.3 Storage Conditions

To prevent moisture absorption, which can cause \"popcorning\" during reflow, specific storage conditions are mandated. In its original sealed moisture-proof bag with desiccant, the device should be stored at ≤30°C and ≤90% RH and used within one year. Once the bag is opened, the components should be stored at ≤30°C and ≤60% RH and ideally processed within one week. For longer storage outside the original packaging, baking at approximately 60°C for at least 20 hours before soldering is required.

5.4 Cleaning

If post-solder cleaning is required, only alcohol-based solvents like isopropyl alcohol should be used. Harsh or aggressive chemical cleaners should be avoided as they may damage the package material or the lens.

6. Packaging and Ordering Information

6.1 Tape and Reel Specifications

The component is supplied on embossed carrier tape with a protective cover tape. The tape width is 8mm, wound on a standard 7-inch (178mm) diameter reel. Each reel contains 3000 pieces. The packaging conforms to ANSI/EIA 481-1-A-1994 specifications, ensuring compatibility with automated feeders.

7. Application Suggestions and Design Considerations

7.1 Typical Circuit Configuration

The most common operating mode for a photodiode like the LTR-C155DD-G is the photoconductive mode. Here, the diode is reverse-biased with a voltage (e.g., 5V, as in the test condition). The photocurrent generated is proportional to the light intensity. This current can be converted to a voltage using a load resistor (RL). The value of RL affects both the output voltage swing and the bandwidth (speed) of the circuit due to the RC time constant formed with the photodiode's junction capacitance (CT). For high-speed applications like 38 kHz IR remote control decoding, a smaller RL (e.g., 1kΩ to 10kΩ) is used. For higher sensitivity in low-light conditions, a larger RL or a transimpedance amplifier (TIA) circuit is recommended.

7.2 Optical Design Considerations

To optimize performance, the infrared source (IRED) should have an emission wavelength matching the photodiode's peak sensitivity (around 940nm). An optical filter can be placed in front of the photodiode to block visible light, significantly improving the signal-to-noise ratio in environments with strong ambient light. The wide viewing angle of the photodiode simplifies optical alignment but may also make it more susceptible to stray light; mechanical shrouding can help define the field of view.

7.3 Layout Considerations

Follow the recommended solder pad layout to ensure good solderability and mechanical strength. In sensitive analog circuits, keep the traces from the photodiode anode and cathode as short as possible to minimize noise pickup and parasitic capacitance. Proper grounding and shielding may be necessary in electrically noisy environments.

8. Technical Comparison and Differentiation

Compared to a phototransistor, a photodiode like the LTR-C155DD-G offers a faster response time (sub-microsecond vs. microseconds), making it superior for high-speed data transmission or modulated signal reception. It also provides a more linear output relative to light intensity. Compared to other photodiodes, its key features include a standardized package for automated assembly, compatibility with lead-free reflow, and a specified high-speed performance suitable for consumer IR protocols.

9. Frequently Asked Questions (Based on Technical Parameters)

9.1 What is the difference between Reverse Light Current (Ip) and Short Circuit Current (Is)?

Reverse Light Current (Ip) is measured with the photodiode under a reverse bias voltage (e.g., 5V). This is the standard operating condition for linear response and speed. Short Circuit Current (Is) is measured with zero volts across the diode (photovoltaic mode). The typical value is similar, but the photovoltaic mode has a slower response and a voltage-dependent current output.

9.2 How do I choose the load resistor (RL) value?

The choice involves a trade-off between bandwidth and signal amplitude. For a 38kHz IR signal, the period is about 26µs. The rise/fall time of the photodiode (0.3µs) is much faster than this, so it's not the limiting factor. The RC time constant (RL * CT) should be significantly smaller than the pulse width you need to detect. For a 1kΩ resistor and 14pF capacitance, the time constant is 14ns, which is excellent for high speed. A larger RL gives a larger output voltage for the same light level but reduces bandwidth and may increase noise.

9.3 Why is baking required if the parts are stored outside the bag?

Plastic SMT packages can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating internal pressure that can delaminate the package or crack the die—a phenomenon known as \"popcorning.\" Baking drives out this absorbed moisture, preventing this failure mode.

10. Operational Principle Introduction

A photodiode is a semiconductor PN junction. When photons with energy greater than the semiconductor's bandgap strike the depletion region of the junction, they can excite electrons from the valence band to the conduction band, creating electron-hole pairs. Under the influence of the internal electric field (inherent in the junction or enhanced by an external reverse bias voltage), these charge carriers are swept apart, generating a measurable current in an external circuit. This photocurrent is directly proportional to the intensity of the incident light, provided the device operates within its linear region. The peak wavelength of sensitivity is determined by the bandgap energy of the semiconductor material used.

11. Development Trends

The trend in discrete infrared sensors like photodiodes is towards further miniaturization of packages while maintaining or improving performance parameters such as lower dark current, higher speed, and enhanced resistance to ambient light interference. Integration is another key trend, with devices combining the photodiode with a dedicated amplifier, filter, and digital logic in a single package to create complete \"IR receiver modules\" that simplify end-product design. There is also a continuous drive for higher reliability and compatibility with increasingly stringent environmental and manufacturing standards, such as those for automotive or industrial applications.