LTST-C171KDWT SMD LED Datasheet - White Diffused Lens - AlInGaP Red Chip - 30mA Forward Current - 75mW Power Dissipation - English Technical Document

1. Product Overview

The LTST-C171KDWT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It belongs to a family of miniature components engineered for space-constrained applications across a broad spectrum of modern electronic equipment.

1.1 Core Advantages and Target Market

This LED leverages an Ultra Bright AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor chip to produce red light, which is then diffused through a white lens. This combination aims for high luminous intensity with a wide, uniform viewing angle. Its primary advantages include compatibility with automated pick-and-place machinery and infrared (IR) reflow soldering processes, which are standard in high-volume electronics manufacturing. The device is RoHS compliant, meeting environmental regulations. Target applications span telecommunications (e.g., cellular phones), office automation (e.g., notebook computers, network systems), home appliances, industrial equipment, and specific lighting functions such as keypad/ keyboard backlighting, status indicators, micro-displays, and signal luminaries.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the electrical and optical specifications is critical for reliable circuit design and performance prediction.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. They are specified at an ambient temperature (Ta) of 25°C. The maximum continuous DC forward current (IF) is 30 mA. A higher Peak Forward Current of 80 mA is permissible but only under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width, useful for brief, high-intensity signaling. The maximum power the device can dissipate is 75 mW. The maximum allowable Reverse Voltage (VR) is 5 V; exceeding this can break down the LED's PN junction. The operating and storage temperature ranges are -30°C to +85°C and -40°C to +85°C, respectively.

2.2 Electrical and Optical Characteristics

These are typical performance parameters measured at Ta=25°C and a standard test current (IF) of 20 mA. The Luminous Intensity (Iv) has a wide range from 11.2 mcd (millicandela) minimum to 45.0 mcd maximum, with specific values determined by the binning process. The Viewing Angle (2θ1/2) is 130 degrees, indicating a very wide emission pattern suitable for area illumination or indicators that need to be seen from off-axis positions. The Dominant Wavelength (λd), which defines the perceived color, ranges from 630 nm to 660 nm, placing it in the red region of the spectrum. The typical Forward Voltage (VF) ranges from 1.6 V to 2.4 V at 20 mA. The Reverse Current (IR) is typically very low, with a maximum of 10 µA at the full 5 V reverse bias.

3. Binning System Explanation

To ensure consistency in production, LEDs are sorted into performance categories or \"bins.\"

3.1 Luminous Intensity Binning

The LTST-C171KDWT uses a binning system based on luminous intensity measured at 20 mA. The bins are defined as follows: Bin Code \"L\" covers 11.2 to 18.0 mcd, Bin \"M\" covers 18.0 to 28.0 mcd, and Bin \"N\" covers 28.0 to 45.0 mcd. A tolerance of +/-15% is applied to the intensity within each bin. Designers must specify the required bin when ordering to guarantee the brightness uniformity needed for their application, especially when using multiple LEDs in an array.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet, their implications are standard. The Forward Current vs. Forward Voltage (I-V) curve shows the exponential relationship typical of a diode. The Luminous Intensity vs. Forward Current curve demonstrates how light output increases with current, typically in a near-linear region around the recommended operating point. The Luminous Intensity vs. Ambient Temperature curve is crucial, as LED output generally decreases as temperature rises; understanding this derating is essential for designs operating in elevated temperature environments. The Spectral Distribution graph would show the concentration of emitted light around the peak wavelength of approximately 650 nm.

5. Mechanical and Packaging Information

5.1 Physical Dimensions and Polarity

The LED comes in a standard EIA package footprint. The exact length, width, and height dimensions are provided in millimeters with a typical tolerance of ±0.1 mm. The component features a polarity indicator, crucial for correct orientation during assembly. The cathode is typically marked, often by a green tint on the corresponding side of the package or a notch in the plastic body.

5.2 Recommended PCB Pad Layout

A land pattern design is suggested to ensure reliable soldering and proper mechanical stability. This pattern specifies the size and shape of the copper pads on the PCB, including any thermal relief or solder mask definitions, to optimize the solder joint formation during reflow.

5.3 Tape and Reel Packaging

For automated assembly, the LEDs are supplied on 8mm wide embossed carrier tape wound onto 7-inch (178 mm) diameter reels. Each reel contains 3000 pieces. The packaging follows ANSI/EIA 481 specifications. Key notes include: empty pockets in the tape are sealed with cover tape, a minimum order quantity for remnants is 500 pieces, and a maximum of two consecutive missing components are allowed per reel.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Conditions

The device is qualified for lead-free (Pb-free) soldering processes. The recommended peak reflow temperature is 260°C, and the time above this peak temperature should not exceed 10 seconds. A complete thermal profile including pre-heat stages (e.g., 150-200°C for up to 120 seconds) is recommended to prevent thermal shock and ensure proper solder paste activation. The datasheet references JEDEC standards as a basis for profile development, emphasizing that the final profile must be characterized for the specific PCB design, solder paste, and oven used.

6.2 Storage and Handling

The LEDs are moisture-sensitive. When sealed in their original moisture-proof bag with desiccant, they should be stored at ≤ 30°C and ≤ 90% RH and used within one year. Once the bag is opened, the \"floor life\" is limited. For MSL 2a (Moisture Sensitivity Level 2a), components should be IR-reflowed within 672 hours (28 days) of exposure to ambient factory conditions (≤ 30°C / 60% RH). For longer exposure, baking at approximately 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" damage during reflow. Electrostatic discharge (ESD) precautions are mandatory; using grounded wrist straps and workstations is advised.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable. Unspecified or aggressive chemicals may damage the plastic lens or package.

7. Application Notes and Design Considerations

7.1 Drive Circuit Design

LEDs are current-driven devices. To ensure consistent brightness and prevent current hogging, it is strongly recommended to use a series current-limiting resistor for each LED, even when multiple LEDs are connected in parallel to a voltage source. The resistor value (R) is calculated using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the forward voltage of the LED (use max value from datasheet for reliability), and IF is the desired forward current. Driving LEDs directly from a voltage source without current regulation is not recommended as it can lead to thermal runaway and device failure.

7.2 Thermal Management

Although the power dissipation is relatively low (75 mW max), effective thermal management on the PCB is still important for long-term reliability and maintaining luminous intensity. Ensuring adequate copper area around the LED's thermal pad (if applicable) and general PCB ventilation helps dissipate heat, especially in high ambient temperature applications or when driving the LED near its maximum current rating.

7.3 Application Scope and Limitations

This LED is intended for general-purpose electronic equipment. The datasheet explicitly cautions against using it in safety-critical applications where failure could jeopardize life or health—such as aviation, transportation control, medical devices, or life-support systems—without prior consultation and specific qualification.

8. Technical Comparison and Differentiation

The key differentiator of the LTST-C171KDWT is its use of an AlInGaP chip with a white diffused lens. Compared to traditional GaAsP or GaP red LEDs, AlInGaP technology typically offers higher efficiency and better performance stability over temperature. The white diffused lens provides a wider and more uniform viewing angle compared to a clear or water-clear lens, which often has a more focused beam. This makes it superior for applications requiring wide-area, soft illumination rather than a directed spotlight.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED at 30 mA continuously?

A: Yes, 30 mA is the maximum rated continuous DC forward current. For optimal longevity, operating slightly below this maximum, such as at 20 mA (the standard test condition), is often recommended.

Q: What is the difference between Dominant Wavelength and Peak Wavelength?

A: Peak Wavelength (λp) is the single wavelength at which the emission spectrum is strongest. Dominant Wavelength (λd) is derived from the color coordinates on the CIE chromaticity diagram and represents the single wavelength that best matches the perceived color of the light. λd is more relevant for color specification.

Q: Why is a series resistor necessary even for a constant voltage supply?

A: The forward voltage (VF) of an LED has a manufacturing tolerance and decreases with increasing temperature. A constant voltage source would cause the current to increase uncontrollably as the LED heats up, potentially leading to thermal runaway. A series resistor provides negative feedback, stabilizing the current.

10. Practical Design and Usage Case

Scenario: Designing a status indicator panel for a network router. The panel requires four uniformly bright red status LEDs. The system uses a 5V rail. Design steps: 1) Select the required luminous intensity bin (e.g., Bin \"M\" for 18-28 mcd). 2) Calculate the series resistor. Using the maximum VF of 2.4V and a target IF of 20 mA: R = (5V - 2.4V) / 0.02A = 130 Ω. The nearest standard value of 130 Ω or 150 Ω can be used. 3) Design the PCB layout using the recommended pad pattern, ensuring correct polarity alignment. 4) Specify the IR reflow profile per the guidelines during PCB assembly. 5) After assembly, verify intensity uniformity under operating conditions.

11. Operating Principle Introduction

An LED is a semiconductor diode. When a forward voltage is applied across its terminals (anode positive relative to cathode), electrons from the n-type semiconductor and holes from the p-type semiconductor are injected into the active region. When these charge carriers recombine, energy is released in the form of photons (light). The specific semiconductor material (AlInGaP in this case) determines the bandgap energy and thus the wavelength (color) of the emitted light. The white diffused lens contains scattering particles that broaden the initially directional light output from the chip, creating a wide, uniform viewing angle.

12. Technology Trends

The general trend in SMD LEDs is toward higher efficiency (more lumens per watt), improved color rendering, and greater reliability. For indicator-type LEDs, miniaturization continues while maintaining or increasing brightness. There is also a focus on expanding the range of available colors and color temperatures. Manufacturing processes are being refined to achieve tighter binning tolerances, providing designers with more consistent performance. The drive for higher temperature tolerance and compatibility with lead-free, high-temperature soldering processes remains a key industry focus.