LTST-S270KGKT SMD LED Datasheet - Side Looking Chip - Green (574nm) - 2.4V - 75mW - English Technical Document

1. Product Overview

The LTST-S270KGKT is a high-brightness, side-looking SMD (Surface Mount Device) LED utilizing an AlInGaP (Aluminum Indium Gallium Phosphide) chip technology. This component is designed for applications requiring a wide viewing angle and reliable performance in automated assembly processes. Its primary function is to serve as a compact, efficient indicator light source.

Core Advantages: The key benefits of this LED include its ultra-bright output from the AlInGaP material system, compatibility with standard infrared reflow soldering processes, and packaging on 8mm tape for high-volume, automated pick-and-place assembly. It is also classified as a green product, meeting RoHS (Restriction of Hazardous Substances) compliance standards.

Target Market: This LED is suitable for a wide range of electronic equipment, including office automation devices, communication equipment, and various household appliances where reliable status indication is required.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat without exceeding its thermal limits.
• DC Forward Current (IF): 30 mA. The maximum continuous forward current that can be applied.
• Peak Forward Current: 80 mA (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width). This allows for brief, higher-current pulses for applications like multiplexing.
• Reverse Voltage (VR): 5 V. Exceeding this voltage in reverse bias can cause breakdown.
• Operating Temperature Range: -30°C to +85°C. The ambient temperature range for reliable operation.
• Storage Temperature Range: -40°C to +85°C.
• Infrared Soldering Condition: Withstands 260°C for 10 seconds, which is typical for lead-free (Pb-free) reflow processes.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard test condition of Ta=25°C and IF=20mA, unless otherwise specified.

• Luminous Intensity (Iv): Ranges from 18.0 mcd (minimum) to 71.0 mcd (maximum), with a typical value provided. This measures the perceived brightness by the human eye.
• Viewing Angle (2θ1/2): 130 degrees. This wide angle indicates the LED emits light over a broad area, making it suitable for side-viewing applications.
• Peak Emission Wavelength (λP): 574 nm. The wavelength at which the optical power output is maximum.
• Dominant Wavelength (λd): 571 nm. This is the single wavelength that best represents the perceived color of the LED, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): 15 nm. This indicates the spectral purity or the spread of wavelengths emitted around the peak.
• Forward Voltage (VF): Typically 2.4V, with a range from 2.0V to 2.8V at 20mA. This is the voltage drop across the LED when it is conducting.
• Reverse Current (IR): 10 μA maximum at VR=5V. A small leakage current when the LED is reverse-biased.

3. Bin Code System Explanation

The LED is sorted into bins based on key parameters to ensure consistency in production runs. Designers must specify the required bin codes when ordering for color and brightness matching.

3.1 Forward Voltage Binning

Binned at 20mA. Tolerance on each bin is ±0.1V.
Bin Codes: 4 (1.90-2.00V), 5 (2.00-2.10V), 6 (2.10-2.20V), 7 (2.20-2.30V), 8 (2.30-2.40V).

3.2 Luminous Intensity Binning

Binned at 20mA. Tolerance on each bin is ±15%.
Bin Codes: M (18.0-28.0 mcd), N (28.0-45.0 mcd), P (45.0-71.0 mcd).

3.3 Dominant Wavelength Binning

Binned at 20mA. Tolerance for each bin is ±1 nm.
Bin Codes: C (567.5-570.5 nm), D (570.5-573.5 nm), E (573.5-576.5 nm).

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1 for spectral distribution, Fig.6 for viewing angle), the data implies standard LED behavior.

• IV Curve: The forward voltage (VF) increases with forward current (IF), following a typical diode exponential relationship. The specified VF @ 20mA is the key design point.
• Temperature Characteristics: Luminous intensity typically decreases as the junction temperature increases. The wide operating temperature range (-30°C to +85°C) indicates stable performance across various environments, though derating may be necessary at high temperatures.
• Spectral Distribution: The peak at 574nm with a 15nm half-width defines the green color. The dominant wavelength (571nm) is the key parameter for color specification in design.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED conforms to an EIA standard package outline for side-looking LEDs. All dimensions are in millimeters with a general tolerance of ±0.10 mm unless otherwise specified. Detailed dimensional drawings are provided in the datasheet for PCB footprint design.

5.2 Pad Design and Polarity

The datasheet includes suggested soldering pad dimensions and orientation. Correct polarity is crucial; the LED has an anode and cathode which must be aligned with the PCB footprint. The package is designed to be compatible with automatic placement equipment.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Parameters

A suggested IR reflow profile for Pb-free process is provided, compliant with JEDEC standards.

• Pre-heat: 150-200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: 10 seconds maximum (recommended for a maximum of two reflow cycles).

Note: The optimal profile depends on the specific PCB design, solder paste, and oven. The provided profile serves as a generic target.

6.2 Hand Soldering

If hand soldering is necessary:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per pad (one time only).

6.3 Storage Conditions

• Sealed Package: Store at ≤30°C and ≤90% RH. Use within one year if the moisture-proof bag with desiccant is intact.
• Opened Package: Store at ≤30°C and ≤60% RH. Use within one week for reflow. For longer storage, use a sealed container with desiccant or a nitrogen desiccator. LEDs stored out of packaging for >1 week should be baked at ~60°C for ≥20 hours before soldering.

6.4 Cleaning

Only use specified cleaning agents. Immerse in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute if cleaning is required. Do not use unspecified chemicals.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

• Packaged in 8mm wide embossed carrier tape.
• Supplied on 7-inch (178mm) diameter reels.
• Quantity per Reel: 4000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Packaging complies with ANSI/EIA-481 specifications.
• Empty pockets are sealed with cover tape.
• A maximum of two consecutive missing components is allowed per reel.

8. Application Suggestions

8.1 Typical Application Scenarios

This side-looking LED is ideal for applications where the light needs to be visible from the edge of a device, such as:

• Status indicators on thin consumer electronics (phones, tablets, laptops).
• Backlighting for side-illuminated panels or symbols.
• Level indicators on audio equipment or instrumentation.
• General-purpose indicator lights in appliances and office equipment.

8.2 Design Considerations

• Current Limiting: Always use a series current-limiting resistor. Calculate based on the supply voltage (Vs), the LED forward voltage (VF from the chosen bin), and the desired forward current (IF, not to exceed 30mA DC). Formula: R = (Vs - VF) / IF.
• ESD Protection: LEDs are sensitive to electrostatic discharge (ESD). Handle with appropriate ESD precautions (wrist straps, grounded workstations).
• Thermal Management: Ensure the PCB layout allows for heat dissipation, especially if operating near maximum current or in high ambient temperatures.
• Optical Design: The 130-degree viewing angle provides wide visibility. Consider this in the mechanical design of light pipes or apertures.

9. Technical Comparison and Differentiation

The LTST-S270KGKT differentiates itself through its material and package:

• AlInGaP vs. Other Technologies: Compared to traditional GaP (Gallium Phosphide) green LEDs, AlInGaP offers significantly higher luminous efficiency and brightness.
• Side-Looking Package: Unlike top-emitting LEDs, this package is specifically designed to emit light from the side, saving vertical space on the PCB and enabling unique aesthetic and functional designs.
• Reflow Compatibility: Its ability to withstand standard SMT reflow profiles makes it suitable for modern, high-volume manufacturing lines alongside other components.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What resistor value should I use with a 5V supply?
A: Using typical VF=2.4V and a target IF=20mA: R = (5V - 2.4V) / 0.02A = 130 Ohms. Use the nearest standard value (e.g., 130Ω or 120Ω). Always consider the minimum and maximum VF from the bin code for worst-case current calculations.

Q: Can I drive this LED with a PWM signal for dimming?
A: Yes. The peak forward current rating of 80mA (pulsed) allows for PWM dimming. Ensure the average current over time does not exceed the DC forward current rating of 30mA.

Q: Why are there different bin codes, and which should I choose?
A: Manufacturing variations cause differences in VF, intensity, and wavelength. Binning ensures consistency within a batch. For color-critical applications (e.g., multi-LED displays), specify a tight wavelength bin (e.g., D). For brightness consistency, specify a tight intensity bin (e.g., P). For general indication, standard bins are acceptable.

Q: Is a heat sink required?
A> At the absolute maximum power dissipation of 75mW and typical operating conditions (20mA * ~2.4V = 48mW), a dedicated heat sink is usually not required for a single LED. However, proper PCB copper pour can aid in heat dissipation, especially in high-temperature environments or when multiple LEDs are clustered.

11. Practical Design and Usage Case

Case: Designing a Status Indicator for a Portable Device
A designer is creating a slim tablet with a side-mounted power/charging indicator. The LTST-S270KGKT is selected for its side-emitting property and low profile.

1. PCB Layout: The LED is placed at the edge of the PCB. The suggested pad layout from the datasheet is used to ensure proper soldering and alignment.
2. Circuit Design: The device uses a 3.3V system rail. A 47Ω resistor is chosen ((3.3V - 2.4V)/0.02A ≈ 45Ω) to drive the LED at approximately 20mA, providing ample brightness.
3. Mechanical Integration: A small light guide channels the light from the side of the LED to a tiny window on the tablet's bezel. The 130-degree viewing angle ensures the light is easily visible from various angles.
4. Manufacturing: The LEDs, supplied on 8mm tape reels, are automatically placed during SMT assembly. The board undergoes a standard lead-free reflow process with a peak temperature of 250°C, well within the LED's 260°C limit.
5. Binning: The designer specifies Bin Code 6 for VF (2.1-2.2V) and Bin Code N for intensity (28-45 mcd) to ensure consistent brightness and color across all production units without requiring the highest (and potentially more costly) bins.

12. Principle Introduction

Light emission in this LED is based on electroluminescence in a semiconductor p-n junction made of AlInGaP materials. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the active region (the junction). When these charge carriers recombine, they release energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy of the semiconductor, which directly dictates the wavelength (color) of the emitted light. In this case, the composition is tuned to produce green light with a peak wavelength around 574 nanometers. The side-looking package incorporates a molded epoxy lens that shapes the light output, creating the characteristic 130-degree viewing angle by refracting and reflecting the light emitted from the chip.

13. Development Trends

The general trend in indicator LEDs like this one is towards several key areas:

• Increased Efficiency: Ongoing material science improvements aim to produce more lumens per watt (lm/W), reducing power consumption for the same light output.
• Miniaturization: There is a continuous push for smaller package sizes while maintaining or improving optical performance, enabling denser PCB layouts and slimmer end products.
• Enhanced Reliability and Robustness: Improvements in packaging materials and die attach technologies lead to longer lifetimes and better performance under harsh environmental conditions (temperature, humidity).
• Integration: Trends include integrating current-limiting resistors or even simple driver ICs within the LED package to simplify circuit design for the end user.
• Color Consistency and Binning: Manufacturing processes are constantly refined to reduce variation, leading to tighter binning specifications and less need for selective sorting in color-critical applications.