LTST-S225KFKGKT-5A Dual Color SMD LED Datasheet - Package Dimensions - Orange/Green - 20mA - English Technical Document

1. Product Overview

The LTST-S225KFKGKT-5A is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, space-constrained electronic applications. It belongs to a family of miniature components optimized for automated printed circuit board (PCB) assembly processes. This particular model integrates two distinct LED chips within a single package, enabling dual-color functionality from a compact footprint.

1.1 Core Advantages and Target Market

The primary advantage of this component is its combination of miniaturization and multi-color capability. It is constructed using ultra-bright AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for both its orange and green emitters, which typically offers higher efficiency and better performance stability compared to older technologies like standard GaP. The package features a water-clear lens, which does not diffuse the light, making it suitable for side-looking applications where the light is intended to be emitted parallel to the PCB surface. This design is ideal for backlighting keypads or keyboards, status indicators in handheld devices, and micro-displays where light needs to be directed sideways. The device is fully compliant with RoHS (Restriction of Hazardous Substances) directives and is designed to be compatible with infrared (IR) reflow soldering processes, which are standard in high-volume electronics manufacturing. Its target markets include telecommunications equipment (e.g., cellular and cordless phones), portable computing devices like notebooks, network system hardware, various home appliances, and indoor signage applications.

2. Technical Parameters: In-Depth Objective Interpretation

This section provides a detailed analysis of the key performance parameters specified for the LTST-S225KFKGKT-5A, based on standard test conditions at an ambient temperature (Ta) of 25°C.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation.

• Power Dissipation (Pd): 50 mW per color chip. This is the maximum amount of electrical power that can be converted into heat and light without damaging the LED. Exceeding this limit risks thermal runaway and failure.
• Peak Forward Current (I_F(PEAK)): 40 mA, permissible only under pulsed conditions with a 1/10 duty cycle and a 0.1ms pulse width. This allows for brief periods of high brightness, such as in flashing indicators.
• Continuous Forward Current (I_F): 20 mA DC. This is the recommended maximum current for continuous, steady-state operation to ensure long-term reliability and maintain specified optical performance.
• Operating Temperature Range: -30°C to +85°C. The device is guaranteed to function within this ambient temperature range.
• Storage Temperature Range: -40°C to +85°C. The device can be stored without applied power within these limits.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured under normal operating conditions (I_F = 5mA).

• Luminous Intensity (I_V): This is the perceived brightness of the LED as measured by the human eye. For the Orange chip, the minimum is 18.0 mcd (millicandela), typical is unspecified, and maximum is 45.0 mcd. For the Green chip, the minimum is 7.1 mcd and maximum is 18.0 mcd. The actual delivered intensity falls into specific bins (see Section 4).
• Viewing Angle (2θ_1/2): 130 degrees (typical). This wide viewing angle indicates the LED emits light over a broad area, which is characteristic of side-view packages with a clear lens. θ_1/2 is the off-axis angle where intensity drops to half its on-axis value.
• Peak Wavelength (λ_P): The wavelength at which the optical output power is greatest. Typical values are 611.0 nm (Orange) and 573.0 nm (Green).
• Dominant Wavelength (λ_d): The single wavelength that best represents the perceived color. Typical values are 605.0 nm (Orange) and 571.0 nm (Green). This value is derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): The bandwidth of the emitted light, measured as the full width at half maximum (FWHM) of the spectrum. Typical values are 17 nm (Orange) and 15 nm (Green), indicating relatively pure, saturated colors.
• Forward Voltage (V_F): The voltage drop across the LED when conducting the specified current. At 5mA, V_F ranges from a minimum of 1.7V to a maximum of 2.5V for both colors. Designers must ensure the driving circuit can accommodate this range.
• Reverse Current (I_R): Maximum 10 μA at a reverse voltage (V_R) of 5V. This parameter is for testing purposes only; the LED is not designed for operation in reverse bias.

3. Bin Ranking System Explanation

To manage production variations, LEDs are sorted into performance bins. The LTST-S225KFKGKT-5A uses a binning system for Luminous Intensity.

3.1 Luminous Intensity Binning

The luminous intensity of each color chip is tested and sorted into specific bins with a tolerance of +/-15% within each bin.

• Orange Chip Bins:
  • Bin Code M: Minimum 18.0 mcd, Maximum 28.0 mcd.
  • Bin Code N: Minimum 28.0 mcd, Maximum 45.0 mcd.
• Green Chip Bins:
  • Bin Code K: Minimum 7.1 mcd, Maximum 11.2 mcd.
  • Bin Code L: Minimum 11.2 mcd, Maximum 18.0 mcd.

This binning allows designers to select components with consistent brightness levels for their application, which is critical for achieving uniform appearance in multi-LED arrays or indicators.

4. Mechanical and Package Information

4.1 Package Dimensions and Pin Assignment

The LED conforms to an EIA standard package outline. All dimensions are in millimeters with a standard tolerance of ±0.1 mm unless otherwise noted. The package is a side-looking type, meaning the primary light emission is parallel to the mounting plane. The pin assignment is crucial for correct operation: Pins 1 and 2 are assigned to the Green LED chip, while Pins 3 and 4 are assigned to the Orange LED chip. Designers must reference the detailed dimensioned drawing in the datasheet for precise placement of solder pads on the PCB.

4.2 Recommended PCB Pad Design and Polarity

The datasheet includes a recommended land pattern (solder pad geometry) for the PCB. Following this recommendation is essential for achieving reliable solder joints, proper alignment, and effective heat dissipation during the reflow process. The pad design also aids in self-alignment of the component during soldering. The cathode pin is typically indicated by a marking on the LED package itself (such as a notch or a dot), which must be aligned with the corresponding marking on the PCB silkscreen.

5. Soldering and Assembly Guidelines

5.1 IR Reflow Soldering Parameters

The component is rated for lead-free (Pb-free) soldering processes. The suggested infrared reflow condition is a peak temperature of 260°C for a maximum of 10 seconds. A sample temperature profile compliant with JEDEC standards is provided as a generic target. Key stages include a pre-heat zone (150-200°C for up to 120 seconds) to gradually heat the board and activate the solder paste flux, followed by the reflow zone where the temperature peaks. It is critical to adhere to the solder paste manufacturer's specifications and the JEDEC profile limits to avoid thermal shock, delamination, or damage to the LED's internal structure. The device should not be subjected to more than two reflow cycles.

5.2 Hand Soldering (Soldering Iron)

If hand soldering is necessary, extreme care must be taken. The recommended maximum iron tip temperature is 300°C, and the contact time with any lead should be limited to a maximum of 3 seconds. This should be performed only once to prevent excessive heat stress.

5.3 Storage and Handling Conditions

Proper handling is vital for reliability. The LEDs are sensitive to Electrostatic Discharge (ESD). It is recommended to use a wrist strap or anti-static gloves and ensure all equipment is grounded. For storage, unopened moisture-proof bags (with desiccant) should be kept at ≤30°C and ≤90% Relative Humidity (RH), with a recommended shelf life of one year. Once the bag is opened, the components are rated at Moisture Sensitivity Level (MSL) 3, meaning they must be subjected to reflow soldering within 168 hours (one week) of exposure to an ambient of ≤30°C/60% RH. If exposed for longer, a bake-out at approximately 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" (package cracking during reflow).

5.4 Cleaning

If cleaning after soldering is required, only specified alcohol-based solvents like isopropyl alcohol (IPA) or ethyl alcohol should be used. The LED should be immersed at normal temperature for less than one minute. Unspecified chemical cleaners may damage the epoxy lens or package.

6. Packaging and Ordering Information

6.1 Tape and Reel Specifications

The LEDs are supplied packaged for automated assembly. They are mounted in 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Standard reel quantity is 4000 pieces. For remainder quantities, the minimum orderable pack size is 500 pieces. The packaging conforms to ANSI/EIA-481 specifications. The tape has a cover tape to seal the component pockets, and there is a specification that no more than two consecutive component pockets may be empty.

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuits

Each LED chip (Green and Orange) must be driven independently. A series current-limiting resistor is mandatory for each chip to set the operating current and protect the LED from overcurrent. The resistor value (R_series) can be calculated using Ohm's Law: R_series = (V_supply - V_F) / I_F. Since V_F can vary from 1.7V to 2.5V, the calculation should use the maximum V_F to ensure the current never exceeds the desired level under worst-case conditions. For a 5V supply and a target I_F of 5mA, using V_F(max)=2.5V gives R_series = (5V - 2.5V) / 0.005A = 500Ω. A standard 510Ω resistor would be a suitable choice. For higher brightness at 20mA, the calculation would be different. The two LEDs can be driven from separate microcontroller GPIO pins or logic circuits.

7.2 Thermal Management

Although the power dissipation is low (50mW per chip), effective thermal management on the PCB is still important for longevity and stable performance. Ensuring the recommended solder pad design is used helps conduct heat away from the LED junction into the PCB copper. Avoid placing the LED in enclosed spaces without airflow, especially if operating at higher currents or in high ambient temperatures.

7.3 Optical Design

The side-looking, water-clear lens produces a wide viewing angle (130°). For applications requiring more focused or diffused light, external light guides, lenses, or diffuser films may be necessary. The clear lens is ideal for applications where the LED itself is not directly visible but its light is channeled, such as in edge-lit panels or light pipes.

8. Technical Comparison and Differentiation

The LTST-S225KFKGKT-5A's key differentiators are its dual-color capability in a single, miniature side-view package and the use of AlInGaP technology for both colors. Compared to older dual-color LEDs that might use different material systems (e.g., GaP for green), using AlInGaP for both can offer more consistent forward voltage characteristics and potentially higher efficiency. The side-view form factor is distinct from top-view LEDs and is specifically designed for applications where light emission parallel to the board is required, saving vertical space. Its compatibility with standard IR reflow and tape-and-reel packaging makes it a drop-in solution for high-volume automated production lines.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive both the Orange and Green LEDs simultaneously at their maximum DC current of 20mA each?

A: Yes, but you must consider the total power dissipation. At 20mA and a typical V_F of ~2.1V, each chip dissipates about 42mW. Simultaneous operation would mean ~84mW total dissipation from the package. While this is below the sum of the individual maximums (50mW+50mW=100mW), it approaches the limit. Thermal management and ambient temperature become critical factors for reliable long-term operation in this scenario.

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

A: Peak Wavelength (λ_P) is the physical measurement of the wavelength where the optical power output is highest. Dominant Wavelength (λ_d) is a calculated value from colorimetry that represents the single wavelength the human eye perceives the color to be. For LEDs with a narrow spectrum, they are often close, but λ_d is the more relevant parameter for color specification in displays or indicators.

Q: The datasheet mentions a \"reverse voltage condition is applied to IR test only.\" What does this mean?

A: This is a clarification. The parameter I_R (Reverse Current) is measured by applying a 5V reverse bias during factory testing to check for leakage. However, the LED is a diode and is not designed to be operated in reverse bias in the actual application. Applying a reverse voltage in a circuit could damage the device.

10. Practical Application Example

Scenario: Dual-Status Indicator for a Network Router

A designer is creating a compact router with two status LEDs (Power and Network Activity) but space for only one LED component on the board. The LTST-S225KFKGKT-5A is an ideal solution.

Implementation: The Green chip is assigned as the \"Power\" indicator (steady on when powered). The Orange chip is assigned as the \"Network Activity\" indicator (blinking on data traffic). Two separate GPIO pins from the router's main microcontroller are used, each connected through a 510Ω current-limiting resistor to the anode of the respective LED chip. The cathodes are connected to ground. The side-view emission allows the light to be coupled into a single, small light pipe that channels it to the front panel. This design saves board space, reduces part count, and provides clear, distinct color-coded status information.

11. Operating Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction of the semiconductor material (in this case, AlInGaP), electrons and holes are injected into the junction region. These charge carriers recombine, releasing energy in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. AlInGaP has a bandgap suitable for producing light in the red, orange, and yellow parts of the spectrum, and with specific doping, can also produce green light. The side-view package incorporates the semiconductor chip mounted on a lead frame, wire-bonded, and encapsulated in a clear epoxy resin that forms the lens, directing the light output sideways.

12. Technology Trends

The general trend in SMD LEDs like this one is toward continued miniaturization, increased efficiency (more light output per watt of electrical input), and higher reliability. The adoption of AlInGaP for green emitters, as seen here, represents a move away from traditional, less efficient materials. Furthermore, there is a growing emphasis on precise binning and tighter tolerances to meet the demands of applications requiring high color consistency, such as full-color displays assembled from discrete LEDs. Packaging advancements also focus on improving thermal performance to allow higher drive currents in smaller packages and enhancing compatibility with lead-free, high-temperature soldering processes.