LTST-C191KGKT SMD LED Datasheet - 0.55mm Thin - 2.4V Max - 75mW - Green - English Technical Document

1. Product Overview

The LTST-C191KGKT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. Its miniature footprint and low profile make it ideal for space-constrained applications across a wide range of consumer and industrial electronics.

1.1 Features

• Compliant with RoHS environmental standards.
• Extremely thin package profile measuring only 0.55 mm in height.
• Utilizes an ultra-bright AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor die to produce green light.
• Packaged on 8mm tape wound onto 7-inch diameter reels for compatibility with high-speed automated pick-and-place equipment.
• Standard EIA (Electronic Industries Alliance) package outline.
• Input logic compatible, suitable for direct drive from integrated circuits.
• Designed for use with infrared (IR) reflow soldering processes.

1.2 Applications

This LED is suitable for various illumination and indication purposes, including:

• Backlighting for keypads, keyboards, and micro-displays.
• Status and power indicators in telecommunications equipment, office automation devices, home appliances, and industrial control systems.
• Signal and symbolic luminaires.

2. Mechanical and Package Information

The device features a water-clear lens that allows the green light from the AlInGaP chip to be emitted efficiently. Detailed dimensional drawings are provided in the datasheet, with all critical measurements specified in millimeters. Key package characteristics include a standard footprint designed for reliable soldering and a low profile that minimizes overall assembly height. The polarity is clearly marked on the device body for correct PCB orientation.

3. Technical Parameters: In-Depth Objective Interpretation

3.1 Absolute Maximum Ratings

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

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat without degrading performance or reliability.
• DC Forward Current (IF): 30 mA. The maximum continuous current that can be applied to the LED.
• Peak Forward Current: 80 mA, permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to briefly achieve higher light output.
• Reverse Voltage (VR): 5 V. Exceeding this voltage in reverse bias can cause immediate junction breakdown.
• Operating & Storage Temperature Range: -55°C to +85°C. Specifies the full environmental range for device functionality and non-operational storage.
• Infrared Soldering Condition: Withstands 260°C peak temperature for 10 seconds, which is critical for lead-free (Pb-free) assembly processes.

3.2 Electrical and Optical Characteristics

These parameters are measured at a standard test condition of Ta=25°C and IF=20mA, providing the typical performance benchmarks.

• Luminous Intensity (Iv): Ranges from 18.0 to 71.0 millicandelas (mcd). This wide range is managed through a binning system (see Section 4).
• Viewing Angle (2θ½): 130 degrees. This wide viewing angle indicates a Lambertian or near-Lambertian emission pattern, suitable for area illumination rather than focused beams.
• Peak Emission Wavelength (λP): Typically 574.0 nm. This is the wavelength at which the spectral power distribution is highest.
• Dominant Wavelength (λd): Specified between 567.5 nm and 576.5 nm. This defines the perceived color (green) of the LED and is also subject to binning.
• Spectral Line Half-Width (Δλ): Approximately 15 nm. This indicates the spectral purity or bandwidth of the emitted green light.
• Forward Voltage (VF): Between 1.9 V and 2.4 V at 20mA. The voltage drop across the LED when operating, important for driver circuit design.
• Reverse Current (IR): Maximum of 10 µA at VR=5V. A measure of the junction's leakage in the off-state.

4. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-C191KGKT uses three independent binning criteria.

4.1 Forward Voltage (Vf) Rank

Bins ensure LEDs have similar voltage drops, simplifying current-limiting circuit design. Bins range from Code 4 (1.90V-2.00V) to Code 8 (2.30V-2.40V), each with a ±0.1V tolerance.

4.2 Luminous Intensity (Iv) Rank

Groups LEDs by their light output intensity. Codes are M (18.0-28.0 mcd), N (28.0-45.0 mcd), and P (45.0-71.0 mcd), each with a ±15% tolerance.

4.3 Hue (Dominant Wavelength) Rank

Sorts LEDs by their precise shade of green. Codes are C (567.5-570.5 nm), D (570.5-573.5 nm), and E (573.5-576.5 nm), each with a ±1 nm tolerance.

5. Performance Curve Analysis

The datasheet includes typical characteristic curves that provide deeper insight into device behavior under varying conditions.

• Forward Current vs. Forward Voltage (I-V Curve): Shows the exponential relationship, crucial for determining the required drive voltage for a target current.
• Luminous Intensity vs. Forward Current: Demonstrates how light output increases with current, typically in a near-linear relationship within the operating range before efficiency drops at very high currents.
• Luminous Intensity vs. Ambient Temperature: Illustrates the thermal derating of light output. As junction temperature rises, luminous efficiency generally decreases.
• Spectral Distribution: A plot of relative intensity versus wavelength, showing the peak at ~574nm and the ~15nm half-width, confirming the green color point.

6. Soldering and Assembly Guidelines

6.1 Recommended IR Reflow Profile (Pb-Free)

A critical process for reliable attachment. The profile should include a pre-heat zone (150-200°C), a controlled ramp to a peak temperature not exceeding 260°C, and a time at peak temperature (e.g., 260°C) limited to a maximum of 10 seconds. The entire process should be completed within a maximum pre-heat time of 120 seconds. This profile is based on JEDEC standards to prevent thermal damage to the LED package or die.

6.2 PCB Attachment Pad Design

A recommended land pattern (footprint) is provided to ensure proper solder joint formation, component alignment, and thermal management during reflow.

6.3 Cleaning

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

6.4 Storage and Handling

• ESD Caution: The device is sensitive to electrostatic discharge (ESD). Proper ESD controls (wrist straps, grounded equipment) must be used during handling.
• Moisture Sensitivity: The package is rated MSL2a. Once the original moisture-proof bag is opened, the components must be IR-reflowed within 672 hours (28 days) under storage conditions of ≤30°C and ≤60% RH. For longer storage out of the original bag, baking at 60°C for at least 20 hours is required before soldering.

7. Packaging and Ordering Information

The LEDs are supplied on 8mm wide embossed carrier tape, sealed with a cover tape. The tape is wound onto standard 7-inch (178mm) diameter reels. Each reel contains 5000 pieces. The packaging conforms to ANSI/EIA-481 specifications. A minimum order quantity of 500 pieces applies for remainder quantities.

8. Application Suggestions and Design Considerations

8.1 Typical Application Circuits

For reliable operation, a current-limiting resistor must be connected in series with the LED. The resistor value (R) can be calculated using Ohm's Law: R = (Vsupply - VF) / IF, where VF is the forward voltage of the chosen bin, and IF is the desired drive current (not to exceed 30mA DC).

8.2 Thermal Management

While the power dissipation is low, maintaining the junction temperature within limits is key to long-term reliability and stable light output. Ensure the PCB pad design provides adequate thermal relief, especially when operating at or near the maximum forward current.

8.3 Optical Design

The 130-degree viewing angle provides a wide, diffuse light pattern. For more focused light, secondary optics (lenses or light guides) would be required. The water-clear lens is suitable for applications where the LED chip itself is not visible.

9. Technical Comparison and Differentiation

The primary differentiating features of the LTST-C191KGKT are its ultra-thin 0.55mm profile and the use of an AlInGaP chip for green emission. Compared to older technologies like GaP, AlInGaP offers significantly higher luminous efficiency and better color saturation. The thin profile is a key advantage over standard 0.6mm or 0.8mm chip LEDs in modern, slim consumer devices.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly from a 3.3V or 5V logic output?
A: No. You must use a series current-limiting resistor. A 3.3V supply with a typical VF of 2.1V leaves 1.2V across the resistor. For 20mA, R = 60Ω. Always calculate based on the maximum VF from your specific bin to ensure sufficient current.

Q: What is the difference between Peak Wavelength and Dominant Wavelength?
A> Peak Wavelength (λP) is the physical wavelength of highest spectral emission. Dominant Wavelength (λd) is the perceptual single wavelength that matches the LED's color as seen by the human eye, calculated from the CIE chromaticity diagram. λd is more relevant for color specification.

Q: How do I interpret the bin codes when ordering?
A> You can specify a combination of Vf, Iv, and λd bin codes to obtain LEDs with tightly grouped electrical and optical characteristics, which is essential for consistent performance in multi-LED arrays or backlighting applications.

11. Practical Use Case Example

Scenario: Designing a low-power status indicator for a portable device.
The device runs on a 3.0V coin cell battery. The goal is a clear, green indicator. A drive current of 10mA is chosen to balance brightness and battery life. Assuming a VF bin of 5 (2.05V typical), the series resistor is calculated: R = (3.0V - 2.05V) / 0.01A = 95Ω. A standard 100Ω resistor would be used, resulting in a current of ~9.5mA. An Iv bin of M or N would provide sufficient brightness at this current. The 0.55mm height allows it to fit within an ultra-thin enclosure.

12. Operating Principle Introduction

Light emission in this AlInGaP LED is based on electroluminescence in a semiconductor p-n junction. When a forward voltage is applied, electrons and holes are injected across the junction and recombine in the active region. The energy released during this recombination is emitted as photons (light). The specific composition of the AlInGaP semiconductor alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light, in this case, green. The water-clear epoxy lens encapsulates and protects the semiconductor die while also shaping the light output pattern.

13. Technology Trends

The development of SMD LEDs like the LTST-C191KGKT follows several key industry trends: Miniaturization (thinner, smaller packages), Increased Efficiency (higher luminous output per unit of electrical input, driven by improved epitaxial growth and chip design), and Enhanced Reliability (better packaging materials and processes to withstand higher reflow temperatures and harsher environmental conditions). The move towards AlInGaP for green is part of a broader shift from traditional lower-efficiency materials to higher-performance compound semiconductors across the visible spectrum.