LTST-C191KFKT Orange SMD LED Datasheet - Dimensions 1.6x0.8x0.55mm - Voltage 2.4V - Power 75mW - English Technical Document

1. Product Overview

The LTST-C191KFKT is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, space-constrained electronic applications. It belongs to a category of extra-thin chip LEDs, featuring a remarkably low profile height of only 0.55 millimeters. This makes it an ideal choice for backlighting indicators, status lights, and decorative lighting in slim consumer electronics, automotive interiors, and portable devices where vertical space is at a premium.

The LED utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for its light-emitting region. This technology is renowned for producing high-efficiency light in the amber to red-orange spectrum with excellent brightness and color stability. The device is housed in a water-clear lens package that allows for high light output and a wide viewing angle. It is fully compliant with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product suitable for global markets with stringent environmental regulations.

1.1 Core Advantages and Target Market

The primary advantages of this LED stem from its combination of miniaturization and performance. The ultra-thin 0.55mm profile is its most distinctive feature, enabling design integration into products where traditional LEDs cannot fit. Despite its small size, it delivers high luminous intensity, with typical values reaching 90 millicandelas (mcd). The package conforms to EIA (Electronic Industries Alliance) standard dimensions, ensuring compatibility with a vast ecosystem of automated pick-and-place equipment used in high-volume manufacturing. Furthermore, it is designed to withstand infrared (IR) reflow soldering processes, which is the standard method for assembling surface-mount components onto printed circuit boards (PCBs). This combination targets markets including consumer electronics (smartphones, tablets, wearables), automotive dashboard and control panel lighting, industrial control panels, and general-purpose indicator applications requiring reliable, bright, and compact light sources.

2. Technical Parameters: In-Depth Objective Interpretation

This section provides a detailed analysis of the electrical, optical, and thermal parameters that define the LED's operational boundaries and performance.

2.1 Absolute Maximum Ratings

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

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat without degrading its performance or lifespan. Exceeding this limit risks overheating the semiconductor junction.
• DC Forward Current (IF): 30 mA. The maximum continuous forward current that can be applied to the LED under DC conditions.
• Peak Forward Current: 80 mA. This higher current is permissible only under pulsed conditions, specifically at a 1/10 duty cycle with a 0.1ms pulse width. This rating is relevant for multiplexing or PWM (Pulse Width Modulation) dimming applications.
• Operating Temperature Range: -30°C to +85°C. The ambient temperature range within which the LED is guaranteed to function according to its specifications.
• Storage Temperature Range: -40°C to +85°C. The temperature range for storing the device when it is not powered.
• Infrared Soldering Condition: 260°C for 10 seconds. This defines the peak temperature and time profile the LED can withstand during a lead-free reflow soldering process without damage.

2.2 Electrical & Optical Characteristics

These parameters are measured at a standard ambient temperature of 25°C and define the typical performance of the device.

• Luminous Intensity (Iv): 45.0 (Min), 90.0 (Typ) mcd at IF=20mA. This measures the perceived brightness of the LED as seen by the human eye. The wide range indicates a binning system is used (see Section 3).
• Viewing Angle (2θ1/2): 130 degrees (Typ). This is the full angle at which the luminous intensity drops to half of its value at the central axis (0 degrees). A 130-degree angle indicates a very wide, diffuse light emission pattern suitable for area illumination or wide-viewing indicators.
• Peak Emission Wavelength (λP): 611 nm (Typ). The specific wavelength at which the optical power output of the LED is at its maximum. For this orange LED, it falls in the orange-red part of the visible spectrum.
• Dominant Wavelength (λd): 605 nm (Typ). This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color of the light. It is the key parameter for color specification.
• Spectral Line Half-Width (Δλ): 17 nm (Typ). This indicates the spectral purity or bandwidth of the emitted light. A value of 17nm is typical for AlInGaP LEDs and results in a saturated orange color.
• Forward Voltage (VF): 2.0 (Min), 2.4 (Typ) V at IF=20mA. The voltage drop across the LED when it is conducting the specified current. This is crucial for designing the current-limiting circuitry.
• Reverse Current (IR): 10 µA (Max) at VR=5V. The small leakage current that flows when a reverse voltage is applied. Exceeding the maximum reverse voltage (not specified, but typically around 5V) can cause immediate damage.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The datasheet provides a bin code list specifically for luminous intensity.

3.1 Luminous Intensity Binning

The intensity is measured at the standard test condition of 20mA forward current. The bins are defined as follows:

• Bin Code P: 45.0 mcd (Min) to 71.0 mcd (Max)
• Bin Code Q: 71.0 mcd (Min) to 112.0 mcd (Max)
• Bin Code R: 112.0 mcd (Min) to 180.0 mcd (Max)
• Bin Code S: 180.0 mcd (Min) to 280.0 mcd (Max)

A tolerance of +/-15% is applied to each intensity bin. This means an LED labeled as Bin Q could have an actual intensity between approximately 60.4 mcd and 128.8 mcd. Designers must account for this variation when specifying brightness levels for their application, often designing for the minimum value of the selected bin to guarantee performance.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1, Fig.6), their typical behavior can be described based on the technology.

4.1 Current vs. Voltage (I-V) Characteristic

Like all diodes, the LED has a non-linear I-V curve. Below the forward voltage threshold (around 1.8-2.0V for AlInGaP), very little current flows. As the voltage approaches and exceeds VF (2.4V typical), the current increases exponentially. This is why LEDs must be driven by a current source or via a voltage source with a series current-limiting resistor; a small change in voltage can cause a large, potentially destructive, change in current.

4.2 Luminous Intensity vs. Forward Current

The light output (luminous intensity) is approximately proportional to the forward current over a significant range. However, efficiency may drop at very high currents due to increased heat generation within the chip. The rated 20mA test condition is a standard point that balances brightness, efficiency, and reliability.

4.3 Temperature Dependence

The performance of LEDs is temperature-sensitive. As the junction temperature increases:

• Forward Voltage (VF): Decreases slightly.
• Luminous Intensity (Iv): Decreases. AlInGaP LEDs exhibit less thermal quenching than some other types, but output still declines with rising temperature.
• Dominant Wavelength (λd): May shift slightly, typically to longer wavelengths (red shift).

Proper thermal management in the application design is essential to maintain consistent color and brightness over the product's lifetime.

5. Mechanical & Package Information

The LTST-C191KFKT uses a standard chip LED package format.

5.1 Package Dimensions

The key dimensions are: Length: 1.6mm, Width: 0.8mm, Height: 0.55mm. All tolerances are typically ±0.10mm unless otherwise noted. The package has two metallized terminals (anode and cathode) on the bottom for soldering. The polarity is usually indicated by a marking on the top of the package or a chamfered corner.

5.2 Suggested Soldering Pad Layout

The datasheet includes a recommended land pattern (solder pad) design for the PCB. Following this guideline is critical for achieving reliable solder joints, preventing tombstoning (where one end lifts), and ensuring proper alignment during automated assembly. The pad design accounts for the necessary solder fillet and prevents solder bridging between the two closely spaced terminals.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

The LED is compatible with infrared (IR) reflow soldering processes, which is standard for SMD assembly. A suggested profile is provided, compliant with JEDEC standards for lead-free solder (SnAgCu). Key parameters include:

• Pre-heat: 150-200°C to gradually heat the board and components, activating the flux and minimizing thermal shock.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus: The time within which the solder is molten, typically 60-90 seconds, with a peak of 10 seconds maximum at 260°C.

The profile should be characterized for the specific PCB design, solder paste, and oven used.

6.2 Hand Soldering

If manual soldering is necessary, extreme care must be taken:

• Soldering Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per joint.
• Limit: Only one soldering cycle is recommended to prevent thermal damage to the plastic package and the internal wire bonds.

6.3 Cleaning

Only specified cleaning agents should be used. Unspecified chemicals may damage the plastic lens or the epoxy encapsulant. If cleaning is required post-soldering, immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is recommended.

6.4 Storage and Handling

LEDs are moisture-sensitive devices (MSD). The package is sealed with desiccant. Once opened, the components should be used within 672 hours (28 days) under controlled humidity (<60% RH) or baked before use to remove absorbed moisture, which can cause \"popcorning\" (package cracking) during reflow. Proper ESD (Electrostatic Discharge) precautions, such as using grounded wrist straps and workstations, are mandatory to prevent damage from static electricity.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in industry-standard embossed carrier tape on 7-inch (178mm) diameter reels to facilitate automated assembly.

• Pocket Pitch: Standard 8mm tape.
• Quantity per Reel: 5000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Cover Tape: Empty pockets are sealed with a top cover tape.
• Missing Lamps: A maximum of two consecutive missing LEDs is allowed per the specification (ANSI/EIA 481).

8. Application Suggestions

8.1 Typical Application Scenarios

• Status Indicators: Power, connectivity, battery charge, and mode indicators in ultra-thin laptops, tablets, and smartphones.
• Backlighting: Illumination for membrane switches, keypads, and icons on automotive dashboards, industrial control panels, and medical devices.
• Decorative Lighting: Accent lighting in consumer electronics where a slim form factor is essential.

8.2 Design Considerations

• Current Drive: LEDs are current-operated devices. Always use a series current-limiting resistor when driving from a voltage source. The resistor value can be calculated using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage, and IF is the desired forward current (e.g., 20mA).
• Parallel Connection: Avoid connecting multiple LEDs directly in parallel from a single current source. Small variations in VF between individual LEDs can cause severe current imbalance, with one LED hogging most of the current and potentially failing. Use a separate current-limiting resistor for each LED or dedicated LED driver ICs with multiple channels.
• Thermal Management: Ensure the PCB layout provides adequate thermal relief. Although the power is low (75mW max), continuous operation at high ambient temperatures can reduce light output and lifespan. Avoid placing the LED near other heat-generating components.

9. Technical Comparison and Differentiation

The primary differentiation of the LTST-C191KFKT lies in its ultra-thin 0.55mm profile. Compared to standard 0603 or 0402 package LEDs which are typically 0.6-0.8mm tall, this device offers a ~30% reduction in height. This is a critical advantage in the trend towards ever-thinner electronic products. Its use of AlInGaP technology provides higher efficiency and better color stability in the orange/amber range compared to older technologies like GaAsP. Furthermore, its compatibility with standard IR reflow and pick-and-place processes means it can be integrated into existing high-volume manufacturing lines without requiring special equipment or procedures, unlike some niche ultra-thin components.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 Can I drive this LED at 30mA continuously?

While the Absolute Maximum Rating for DC forward current is 30mA, the standard test condition and typical operating point is 20mA. Operating at 30mA continuously will generate more heat, potentially reducing luminous efficiency and long-term reliability. It is generally recommended to design for 20mA or less for optimal performance and lifespan.

10.2 Why is there such a wide range in the Luminous Intensity specification (45-280 mcd)?

This range represents the total spread across all bin codes (P through S). A specific order will be for a single bin (e.g., Bin Q: 71-112 mcd). The binning system allows manufacturers to sort parts by performance, enabling customers to select the brightness grade that fits their application and cost requirements. Always specify the desired bin code when ordering.

10.3 What is the difference between Peak Wavelength (611nm) and Dominant Wavelength (605nm)?

Peak Wavelength (λP) is the physical wavelength where the optical power output is highest. Dominant Wavelength (λd) is a calculated value based on human color perception (CIE diagram) that best matches the perceived color. For a monochromatic source like an LED, they are often close, but λd is the standard parameter used to specify the color of the LED for design purposes.

11. Practical Design and Usage Case

Scenario: Designing a status indicator for a slim Bluetooth speaker. The design requires a low-power orange LED to indicate pairing mode. The available space behind the front grille is only 0.6mm. A standard LED would not fit. The LTST-C191KFKT, with its 0.55mm height, is selected. The circuit uses a 3.3V microcontroller GPIO pin. The series resistor is calculated: R = (3.3V - 2.4V) / 0.020A = 45 Ohms. A standard 47 Ohm resistor is chosen, resulting in a current of ~19mA. The PCB land pattern is designed according to the datasheet recommendation. The LED is placed in a location with minimal heat from the audio amplifier IC. The chosen bin code is \"Q\" to ensure adequate brightness is achieved even at the lower end of the bin range. The assembly uses a standard lead-free reflow profile with a peak temperature of 250°C.

12. Operating Principle Introduction

An LED is a semiconductor p-n junction diode. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the junction region (the active layer made of AlInGaP). When these electrons and holes recombine, they release energy 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 in the active layer. AlInGaP has a bandgap that corresponds to light in the red, orange, amber, and yellow parts of the spectrum. The water-clear epoxy lens encapsulates the chip, provides mechanical protection, and shapes the light output beam.

13. Technology Trends

The trend in indicator and backlight LEDs continues towards further miniaturization, higher efficiency (more light output per electrical watt), and improved color rendering and consistency. There is also a drive towards integration, such as LEDs with built-in current-limiting resistors or driver ICs. For ultra-thin applications, chip-scale package (CSP) LEDs, which are essentially the bare semiconductor die with a protective coating, represent the next frontier in reducing package size and height. However, devices like the LTST-C191KFKT offer an excellent balance between extreme miniaturization, manufacturability, reliability, and cost for a wide range of current applications.