LTST-C150KGKT SMD LED Datasheet - Ultra Bright Green - 20mA - 75mW - English Technical Document

1. Product Overview

The LTST-C150KGKT is a high-performance, surface-mount LED designed for applications requiring high brightness and reliability. It utilizes an advanced AlInGaP (Aluminum Indium Gallium Phosphide) chip technology to deliver superior luminous intensity in the green spectrum. This component is engineered for compatibility with modern automated assembly processes, including infrared and vapor phase reflow soldering, making it suitable for high-volume manufacturing environments.

Its primary applications include status indicators, backlighting for consumer electronics, automotive interior lighting, and various signaling devices where consistent color output and long-term stability are critical. The device is packaged in industry-standard 8mm tape on 7-inch reels, facilitating efficient pick-and-place operations.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The device is specified for operation within strict environmental and electrical limits to ensure longevity and performance. The absolute maximum ratings define the boundaries beyond which permanent damage may occur.

• Power Dissipation (Pd): 75 mW. This parameter limits the total electrical power that can be converted into heat within the LED package at an ambient temperature (Ta) of 25°C.
• DC Forward Current (IF): 30 mA. The maximum continuous forward current that can be applied.
• Peak Forward Current: 80 mA. This is permissible only under pulsed conditions with a 1/10 duty cycle and a pulse width of 0.1ms, useful for brief, high-intensity flashes.
• Reverse Voltage (VR): 5 V. Exceeding this voltage in the reverse direction can cause junction breakdown.
• Operating & Storage Temperature Range: -55°C to +85°C. This wide range ensures functionality and storage stability in harsh environments.

2.2 Electro-Optical Characteristics

Measured at a standard test condition of Ta=25°C and IF=20mA, these parameters define the core light output performance.

• Luminous Intensity (Iv): Ranges from a minimum of 18.0 mcd to a maximum of 71.0 mcd. The typical value falls within this range, with specific values determined by the binning process.
• Viewing Angle (2θ1/2): 130 degrees. This wide viewing angle indicates a diffuse emission pattern, suitable for applications requiring broad visibility.
• Peak Wavelength (λP): Approximately 574 nm. This is the wavelength at which the spectral power distribution is highest.
• Dominant Wavelength (λd): Approximately 571 nm. This is the single wavelength perceived by the human eye that defines the color of the LED, derived from CIE chromaticity coordinates.
• Spectral Line Half-Width (Δλ): 15 nm. This narrow bandwidth indicates a relatively pure green color.
• Forward Voltage (VF): Typically 2.0 V, with a range defined by voltage binning. This is the voltage drop across the LED when conducting 20mA.
• Reverse Current (IR): Maximum 10 μA at VR=5V, indicating good junction quality.
• Capacitance (C): 40 pF at 0V, 1MHz. This is relevant for high-frequency switching applications.

3. Binning System Explanation

To ensure color and brightness consistency in production, LEDs are sorted into bins based on key parameters. The LTST-C150KGKT uses a three-dimensional binning system.

3.1 Forward Voltage Binning

Units are Volts (V) at IF=20mA. Tolerance per bin is ±0.1V.
Bin Code 4: 1.90V - 2.00V
Bin Code 5: 2.00V - 2.10V
Bin Code 6: 2.10V - 2.20V
Bin Code 7: 2.20V - 2.30V
Bin Code 8: 2.30V - 2.40V

3.2 Luminous Intensity Binning

Units are millicandelas (mcd) at IF=20mA. Tolerance per bin is ±15%.
Bin Code M: 18.0 mcd - 28.0 mcd
Bin Code N: 28.0 mcd - 45.0 mcd
Bin Code P: 45.0 mcd - 71.0 mcd

3.3 Dominant Wavelength Binning

Units are nanometers (nm) at IF=20mA. Tolerance per bin is ±1 nm.
Bin Code C: 567.5 nm - 570.5 nm
Bin Code D: 570.5 nm - 573.5 nm
Bin Code E: 573.5 nm - 576.5 nm

A complete part number includes codes for all three parameters, allowing designers to select LEDs with tightly matched characteristics for their application.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet, their implications are critical for design.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The AlInGaP technology exhibits a relatively stable forward voltage over its operating current range. The typical Vf of 2.0V at 20mA is a key design parameter for current-limiting resistor calculation. Designers must account for the binning range (1.9V to 2.4V) to ensure consistent current drive and therefore consistent brightness across all units in a production run.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to forward current in the normal operating range (up to 30mA DC). Operating above the absolute maximum ratings, even briefly, can cause permanent degradation of light output. The pulsed current rating (80mA) allows for short-duration overdrive for strobe or flash applications without damage.

4.3 Temperature Dependence

Like all semiconductors, LED performance is temperature-sensitive. Luminous intensity typically decreases as junction temperature increases. The wide operating temperature range (-55°C to +85°C) is supported, but designers should note that light output at the extreme high end will be lower than at 25°C. Proper thermal management on the PCB is essential for maintaining performance and longevity, especially when operating near the maximum power dissipation limit.

5. Mechanical & Packaging Information

5.1 Package Dimensions

The LED conforms to an industry-standard SMD package outline. Key dimensional tolerances are ±0.10mm unless otherwise specified. The package features a water-clear lens which does not diffuse the light, contributing to the high axial luminous intensity. Detailed dimensioned drawings are essential for PCB footprint design.

5.2 Polarity Identification

The cathode is typically indicated by a visual marker on the package, such as a notch, a green dot, or a cut corner on the lens. Correct polarity must be observed during assembly to prevent reverse bias damage.

5.3 Soldering Pad Layout

A recommended soldering pad pattern is provided to ensure reliable solder joint formation during reflow. Adhering to these recommendations helps prevent tombstoning (component standing up on one end) and ensures proper alignment and thermal connection.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

The component is compatible with lead-free (Pb-free) soldering processes. The suggested infrared reflow condition specifies a peak temperature not exceeding 260°C for a maximum of 10 seconds. A pre-heat stage of 150-200°C for up to 120 seconds is recommended to minimize thermal shock. The device can withstand a maximum of two reflow cycles under these conditions.

6.2 Hand Soldering

If hand soldering is necessary, use a temperature-controlled iron set to a maximum of 300°C. The soldering time at the lead should not exceed 3 seconds. Hand soldering should be limited to one-time repair only, not for mass production.

6.3 Cleaning

Only specified cleaning agents should be used. Isopropyl alcohol or ethyl alcohol are recommended. The LED should be immersed at normal temperature for less than one minute. Unspecified chemical cleaners may damage the epoxy lens or package material.

6.4 Storage & Handling

For long-term storage, the original sealed packaging with desiccant should be used. The recommended storage environment is below 30°C and 70% relative humidity. Once removed from the moisture-barrier bag, components should be soldered within one week (Moisture Sensitivity Level 3, MSL 3). If stored longer out of the bag, a bake-out at 60°C for 24 hours is required before reflow to prevent "popcorning" (package cracking due to vaporized moisture).

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied on 8mm wide, embossed carrier tape sealed with a cover tape. The tape is wound on standard 7-inch (178mm) diameter reels. Each full reel contains 3000 pieces. A minimum order quantity of 500 pieces is available for remainder quantities. The packaging conforms to ANSI/EIA-481-1-A standards.

7.2 Part Numbering and Binning Selection

The full part number LTST-C150KGKT includes base product information. For production requiring specific performance, bin codes for Forward Voltage (e.g., 5), Luminous Intensity (e.g., N), and Dominant Wavelength (e.g., D) must be specified to obtain parts from the desired bins (e.g., resulting in a tighter-specification code).

8. Application Design Recommendations

8.1 Drive Circuit Design

LEDs are current-driven devices. To ensure uniform brightness, especially when multiple LEDs are connected in parallel, it is strongly recommended to use a series current-limiting resistor for each LED (Circuit Model A). Driving multiple LEDs in parallel from a single voltage source with a shared resistor (Circuit Model B) is not recommended due to variations in individual LED forward voltage (Vf). Even small Vf differences can cause significant current imbalance, leading to visible brightness variations.

The series resistor value (R) is calculated using Ohm's Law: R = (Vsupply - Vf_LED) / I_desired. Use the maximum Vf from the bin range for a conservative design that ensures the current never exceeds the desired value for any LED in the batch.

8.2 Electrostatic Discharge (ESD) Protection

AlInGaP LEDs are sensitive to electrostatic discharge. ESD damage can manifest as high reverse leakage current, low forward voltage, or failure to illuminate at low currents.

Preventive measures are mandatory in handling:
• Use grounded wrist straps and anti-static mats.
• Ensure all equipment and work surfaces are properly grounded.
• Use ionizers to neutralize static charge that may accumulate on the plastic lens during handling.
• Store and transport components in ESD-safe packaging.

To test for potential ESD damage, check if the LED illuminates and measure its Vf at a very low current (e.g., 0.1mA). A healthy AlInGaP LED should have a Vf > 1.4V at 0.1mA.

8.3 Thermal Management

While the package is small, power dissipation (up to 75mW) generates heat. For continuous operation at high currents, consider the PCB layout. Providing adequate copper area (thermal relief pads) around the solder pads helps dissipate heat, maintaining lower junction temperature and ensuring stable light output and longer lifespan.

9. Technical Comparison & Differentiation

The LTST-C150KGKT, based on AlInGaP technology, offers distinct advantages for green light emission compared to older technologies like traditional GaP or modern InGaN-based green LEDs.

Key Advantages:
• Higher Efficiency & Brightness: AlInGaP provides superior luminous efficacy in the amber-to-green spectrum, resulting in higher mcd output per mA of drive current compared to many alternatives.
• Better Temperature Stability: The light output and wavelength shift less with temperature changes compared to some other semiconductor materials.
• Narrower Spectral Width: The 15nm half-width offers a more saturated, pure green color, which is often desirable for indicator and display applications.
• Proven Reliability: AlInGaP is a mature technology with a long history of stable performance in demanding applications.

Designers choosing this LED are typically prioritizing high-brightness green output, color purity, and reliability in a standard SMD package format.

10. Frequently Asked Questions (FAQs)

Q1: Can I drive this LED directly from a 5V microcontroller pin?
A: No. A series resistor is always required. For a 5V supply and a target current of 20mA, assuming a Vf of 2.0V, the resistor value would be R = (5V - 2.0V) / 0.020A = 150 Ohms. Use the maximum Vf from your bin (e.g., 2.4V for Bin 8) for a safe calculation: R = (5V - 2.4V) / 0.020A = 130 Ohms. A 130-150 Ohm resistor is appropriate.

Q2: Why is there a peak current rating (80mA) much higher than the DC rating (30mA)?
A: The LED can handle higher instantaneous power for very short pulses because the heat generated does not have time to raise the junction temperature to a damaging level. This is useful for strobe or communication applications but must adhere strictly to the 1/10 duty cycle and 0.1ms pulse width limits.

Q3: What does "Water Clear" lens mean for the light pattern?
A: A water-clear (non-diffused) lens produces a more focused beam with higher axial intensity (intensity straight ahead). The light pattern will have a more defined central hotspot compared to a diffused lens, which spreads the light more evenly over the wider viewing angle.

Q4: How critical is it to follow the reflow soldering profile exactly?
A: Very critical. Exceeding 260°C or 10 seconds at peak temperature can thermally degrade the epoxy lens, the semiconductor chip, or the internal bond wires, leading to immediate failure or reduced long-term reliability. Always follow the recommended profile.

11. Design-in Case Study Example

Scenario: Designing a status indicator panel for industrial equipment requiring 10 uniformly bright green indicators, visible in high ambient light.

Design Steps:
1. Selection: Choose LTST-C150KGKT for its high brightness (up to 71mcd). Specify tight binning codes (e.g., Voltage Bin 5, Intensity Bin P, Wavelength Bin D) to ensure consistency.
2. Circuit Design: Use a 12V rail. Calculate resistor for worst-case Vf (max from Bin 5 = 2.1V). R = (12V - 2.1V) / 0.020A = 495 Ohms. Use a standard 510 Ohm, 1/8W resistor for each LED in series.
3. PCB Layout: Design pads per datasheet recommendation. Include small thermal relief connections to a slightly larger copper pour for heat dissipation.
4. Assembly: Ensure the contract manufacturer uses the specified reflow profile and handles components with ESD protection.
5. Result: A robust, bright, and uniform indicator panel with reliable performance.

12. Technology Principle Introduction

The LTST-C150KGKT is based on AlInGaP semiconductor material grown on a substrate. When a forward voltage is applied, electrons and holes are injected into the active region where they recombine, releasing energy in the form of photons (light). The specific composition of Aluminum, Indium, Gallium, and Phosphide in the active layer determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, green (~571nm). The water-clear epoxy lens encapsulates the chip, providing mechanical protection, shaping the light output, and enhancing light extraction from the semiconductor.

13. Industry Trends & Context

The trend in indicator and signaling LEDs continues toward higher efficiency (more light per watt), smaller packages, and improved reliability. While newer materials like InGaN (used for blue and true green LEDs) offer high performance, AlInGaP remains the dominant and highly optimized technology for the yellow-green to red spectrum due to its excellent efficiency and stability. The LTST-C150KGKT represents a mature, high-performance solution within this stable technology branch. Future developments may focus on further increasing flux density and integrating driver electronics or color-mixing capabilities into ever-smaller package footprints.