SMD LED LTST-C170KEKT Datasheet - AlInGaP Red - 130° Viewing Angle - 1.6-2.4V - 25mA - English Technical Document

1. Product Overview

The LTST-C170KEKT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It belongs to a family of components engineered for space-constrained applications where reliable, high-brightness indication is required. The device utilizes an Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material to produce a high-efficiency red light output.

1.1 Core Advantages and Target Market

This LED offers several key advantages for modern electronics manufacturing. Its ultra-bright output ensures good visibility even in well-lit environments. The package is compliant with EIA standards, ensuring compatibility with a wide range of automated pick-and-place and assembly equipment. Furthermore, it is designed to withstand standard infrared (IR) reflow soldering processes, making it suitable for high-volume production lines. The primary target markets include telecommunications equipment (such as cellular and cordless phones), office automation devices (notebook computers, network systems), home appliances, and various indoor signage or status indication applications. Its suitability for keyboard backlighting and micro-displays highlights its versatility.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LTST-C170KEKT is defined by a set of electrical, optical, and thermal parameters measured under standard conditions (Ta=25°C).

2.1 Photometric and Optical Characteristics

The luminous intensity (Iv) is a critical parameter, specifying the amount of visible light the LED emits. For this device, the intensity can range from a minimum of 11.2 millicandelas (mcd) to a maximum of 180.0 mcd when driven at a forward current (IF) of 20mA. This wide range is managed through a binning system. The viewing angle, defined as 2θ1/2, is 130 degrees. This indicates a very wide beam pattern, making the LED ideal for applications requiring broad-area illumination rather than a focused spot. The dominant wavelength (λd) ranges from 617 nm to 631 nm, which falls within the red portion of the visible spectrum. The peak emission wavelength (λp) is typically 632 nm.

2.2 Electrical Characteristics

The forward voltage (VF) is the voltage drop across the LED when operating. For the LTST-C170KEKT, VF typically ranges from 1.6V to 2.4V at IF=20mA. This relatively low voltage is beneficial for low-power circuit design. The reverse current (IR) is specified at a maximum of 10 μA when a reverse voltage (VR) of 5V is applied, indicating the device's leakage characteristics under reverse bias.

2.3 Absolute Maximum Ratings and Thermal Considerations

These ratings define the limits beyond which permanent damage may occur. The absolute maximum DC forward current is 25 mA. A higher peak forward current of 60 mA is permissible under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The maximum power dissipation is 62.5 mW. The device can operate within an ambient temperature range of -30°C to +85°C and can be stored from -40°C to +85°C. The maximum allowable reverse voltage is 5V. Exceeding any of these limits may degrade performance or cause failure.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-C170KEKT employs a binning system primarily based on luminous intensity.

3.1 Luminous Intensity Binning

The intensity is categorized into several bins, each denoted by a letter code (L, M, N, P, Q, R). Each bin covers a specific range of luminous intensity measured in mcd at 20mA. For example, bin 'L' covers 11.2 to 18.0 mcd, while bin 'R' covers 112.0 to 180.0 mcd. A tolerance of +/-15% is applied to each bin. This system allows designers to select LEDs with the required brightness level for their specific application, ensuring visual consistency when multiple LEDs are used together.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, typical performance curves for such devices provide valuable insights into behavior under varying conditions.

4.1 Current vs. Voltage (I-V) Characteristic

The I-V curve illustrates the relationship between the forward current and the forward voltage. For AlInGaP LEDs, this curve exhibits a turn-on voltage followed by a region where current increases rapidly with a small increase in voltage. Operating the LED within the specified current range (e.g., 20mA) ensures it lands on the stable, efficient part of this curve.

4.2 Luminous Intensity vs. Forward Current

This curve shows how light output increases with drive current. It is generally linear over a range but will saturate at higher currents. Driving the LED at the recommended 20mA ensures optimal efficiency and longevity, avoiding the thermal stress associated with operation at the absolute maximum current.

4.3 Spectral Distribution

The spectral output curve shows the intensity of light emitted at each wavelength. For a red AlInGaP LED, this curve is typically narrow, centered around the dominant wavelength (617-631 nm), with a spectral half-width (Δλ) of approximately 20 nm. This defines the color purity of the emitted light.

5. Mechanical and Package Information

5.1 Package Dimensions and Polarity Identification

The LED is housed in a standard SMD package. Critical dimensions include the length, width, and height, along with the placement and size of the solder pads. The cathode is typically identified by a visual marker on the package, such as a notch, a dot, or a green marking. Correct polarity orientation during assembly is essential for proper function.

5.2 Recommended PCB Attachment Pad Layout

A suggested land pattern (footprint) for the PCB is provided to ensure reliable soldering and mechanical stability. This pattern defines the size, shape, and spacing of the copper pads onto which the LED is placed before reflow soldering. Adhering to this recommendation helps prevent tombstoning (one end lifting) and ensures good solder fillets.

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Parameters

The device is compatible with lead-free (Pb-free) soldering processes. The recommended peak reflow temperature is 260°C, and the time above this temperature should not exceed 10 seconds. A pre-heat stage (150-200°C) is also specified. These parameters are based on JEDEC standards to prevent thermal damage to the LED's plastic package and internal die.

6.2 Storage and Handling Conditions

LEDs are sensitive to moisture and electrostatic discharge (ESD). When stored in their original sealed moisture-proof bag with desiccant, they have a shelf life. Once the bag is opened, the devices are rated for a specific floor life (e.g., 672 hours for MSL 2a) before they must be reflowed or re-baked to remove absorbed moisture, which can cause \"popcorning\" during soldering. Proper ESD precautions, such as using grounded wrist straps and workstations, are mandatory to prevent damage from static electricity.

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 recommended. Harsh or unspecified chemicals can damage the epoxy lens or package.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

For automated assembly, the LEDs are supplied on embossed carrier tape wound onto 7-inch diameter reels. Each reel typically contains 3000 pieces. The tape dimensions, pocket spacing, and reel hub size conform to industry standards like ANSI/EIA 481, ensuring compatibility with standard feeder equipment.

8. Application Suggestions

8.1 Typical Application Circuits

LEDs are current-driven devices. For consistent brightness, especially when multiple LEDs are used in parallel, it is recommended to drive each LED with its own current-limiting resistor or use a constant-current driver circuit. Connecting LEDs directly in parallel to a single voltage source with one resistor is discouraged due to variations in forward voltage (VF) between individual devices, which can lead to significant brightness mismatch.

8.2 Design Considerations and Cautions

This product is designed for general-purpose electronic equipment. For applications requiring exceptional reliability or where failure could risk safety (e.g., aviation, medical life-support), additional qualification and consultation are necessary. Designers must ensure the operating point (current, voltage, power dissipation) remains within the specified ratings, considering the maximum ambient temperature of the application. Adequate PCB layout for heat dissipation may be required for high-current or high-density applications.

9. Technical Comparison and Differentiation

Compared to older technologies like Gallium Arsenide Phosphide (GaAsP) red LEDs, AlInGaP technology offers significantly higher luminous efficiency, resulting in brighter output at the same drive current. The wide 130-degree viewing angle is a key differentiator from LEDs designed for narrow-beam applications, making it superior for area illumination and status indicators that need to be seen from various angles. Its compatibility with automated IR reflow processes differentiates it from components requiring manual or wave soldering.

10. Frequently Asked Questions Based on Technical Parameters

10.1 Why is there such a wide range in luminous intensity (11.2 to 180 mcd)?

This range represents the total spread across all production units. Through the binning system (L through R), manufacturers sort LEDs into much tighter groups. Designers specify the required bin code when ordering to ensure they receive LEDs with consistent brightness for their application.

10.2 Can I drive this LED at 30mA for more brightness?

No. The absolute maximum continuous forward current is specified as 25 mA. Operating at 30mA exceeds this rating, which can lead to accelerated degradation, reduced lifespan, and potential catastrophic failure due to overheating. For higher brightness, select an LED from a higher intensity bin or a product rated for a higher drive current.

10.3 What is the difference between dominant wavelength and peak wavelength?

Peak wavelength (λp) is the single wavelength at which the emission spectrum has its maximum intensity. Dominant wavelength (λd) is a calculated value derived from the color coordinates on the CIE chromaticity diagram; it represents the perceived color of the light as a single wavelength. For a monochromatic source like a red LED, they are often close, but λd is more relevant for color specification.

11. Practical Application Case Study

Scenario: Backlighting for a Membrane Keypad. A designer is creating a user interface panel with 20 buttons that need red backlighting for use in low-light conditions. The panel is space-constrained, requiring a low-profile component. The LTST-C170KEKT is selected for its SMD format, wide viewing angle (ensuring even illumination under each button), and suitable brightness. The designer chooses LEDs from bin 'M' (18.0-28.0 mcd) to achieve uniform, medium-level brightness across all keys. A constant-current driver IC is used to supply 20mA to each LED individually, ensuring perfect brightness matching regardless of minor VF variations. The PCB layout follows the recommended pad design, and the assembly is done using a standard lead-free reflow profile with a peak of 250°C.

12. Principle of Operation Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction, electrons from the n-type region and holes from the p-type region are injected into the junction region. When these charge carriers recombine, energy is released in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the energy bandgap of the semiconductor material used. For the LTST-C170KEKT, the AlInGaP material system has a bandgap that corresponds to red light.

13. Technology Trends and Developments

The general trend in LED technology is toward higher efficiency (more lumens per watt), improved color rendering, and higher reliability. For indicator LEDs, miniaturization continues while maintaining or increasing light output. There is also a focus on expanding the range of available colors and improving the consistency of color and brightness through advanced manufacturing and binning techniques. The drive for RoHS compliance and compatibility with lead-free, high-temperature soldering processes is now a standard requirement across the industry. Research into new materials and nanostructures promises further efficiency gains and new functionalities in the future.