LTST-C191TBKT-2A Blue SMD LED Datasheet - Dimensions 3.2x1.6x0.55mm - Voltage 2.45-2.95V - Power 76mW - English Technical Document

1. Product Overview

The LTST-C191TBKT-2A is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, space-constrained electronic applications. Its core technology is based on an Indium Gallium Nitride (InGaN) semiconductor chip, which is responsible for emitting blue light. The primary market for this component includes consumer electronics, indicator lights, backlighting for small displays, and various portable devices where a reliable, bright, and compact light source is required.

The defining feature of this LED is its exceptionally low profile, with a height of only 0.55 millimeters. This ultra-thin form factor allows it to be integrated into products with severe vertical space limitations, enabling sleeker and thinner end-product designs. The package uses a water-clear lens material, which does not diffuse the light, resulting in a more focused and intense beam suitable for applications requiring high luminous intensity from a tiny source.

1.1 Core Advantages

• Miniaturization: The 0.55mm height is a significant advantage for ultra-thin product designs.
• High Brightness: Utilizes an Ultra Bright InGaN chip, providing high luminous intensity in a small package.
• Compatibility: Designed to be compatible with automatic pick-and-place equipment and standard infrared (IR) reflow soldering processes, facilitating high-volume, automated assembly.
• Standardization: Conforms to EIA (Electronic Industries Alliance) standard package outlines, ensuring predictability in PCB (Printed Circuit Board) layout and assembly.
• Environmental Compliance: The product is RoHS (Restriction of Hazardous Substances) compliant and classified as a Green Product, meeting international environmental regulations.

2. Technical Parameter Deep-Dive

This section provides an objective analysis of the key electrical, optical, and thermal parameters specified in the datasheet. Understanding these values is critical for proper circuit design and reliable operation.

2.1 Absolute Maximum Ratings

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

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the LED package can dissipate as heat without degrading performance or lifespan. Exceeding this limit risks thermal damage.
• Peak Forward Current (I_FP): 100 mA. This current is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). It is used for applications requiring brief, high-intensity flashes.
• Continuous Forward Current (I_F): 20 mA. This is the maximum recommended current for continuous DC operation. Designing the driver circuit to operate at or below this current ensures long-term reliability.
• Operating Temperature Range (T_opr): -20°C to +80°C. The LED is guaranteed to function within its specified parameters across this ambient temperature range.
• Storage Temperature Range (T_stg): -30°C to +100°C. The device can be stored without operation within these limits without incurring damage.
• IR Reflow Soldering Condition: 260°C peak temperature for a maximum of 10 seconds. This defines the thermal profile the component can withstand during the PCB assembly process.

2.2 Electrical & Optical Characteristics

These parameters are measured at a standard test condition of 25°C ambient temperature and a forward current (I_F) of 2 mA, unless otherwise noted.

• Luminous Intensity (I_V): 4.5 - 18.0 mcd (millicandela). 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 (2θ_1/2): 130 degrees. This is the full angle at which the light intensity drops to half of its maximum value (on-axis). A 130-degree angle indicates a relatively wide viewing pattern.
• Peak Wavelength (λ_P): 468 nm (typical). This is the specific wavelength at which the optical power output is highest. It is a characteristic of the InGaN semiconductor material.
• Dominant Wavelength (λ_d): 465.0 - 475.0 nm. This is derived from the color perceived by the human eye (CIE chromaticity) and is the single wavelength that best represents the LED's color. It is also subject to binning.
• Spectral Bandwidth (Δλ): 25 nm (typical). This indicates the range of wavelengths emitted around the peak. A value of 25nm is typical for a blue InGaN LED.
• Forward Voltage (V_F): 2.45 - 2.95 V. This is the voltage drop across the LED when driven at the test current of 2mA. It varies due to semiconductor manufacturing tolerances and is binned.
• Reverse Current (I_R): 100 µA (max) at a Reverse Voltage (V_R) of 5V. LEDs are not designed for reverse bias operation. This parameter is for leakage current characterization only. Applying reverse voltage can damage the device.

3. Binning System Explanation

To manage natural variations in semiconductor manufacturing, LEDs are sorted into performance groups or \"bins.\" This ensures consistency within a production lot. The LTST-C191TBKT-2A uses a three-dimensional binning system.

3.1 Forward Voltage Binning

Binned at I_F = 2mA. Five bins (1 to 5) cover the range from 2.45V to 2.95V in 0.1V steps, with a +/-0.1V tolerance per bin. This allows designers to select LEDs with a consistent voltage drop, which can be important for current-limiting circuit design, especially in parallel arrays.

3.2 Luminous Intensity Binning

Binned at I_F = 2mA. Three bins (J, K, L) define minimum brightness levels: 4.50-7.10 mcd (J), 7.10-11.2 mcd (K), and 11.2-18.0 mcd (L). A tolerance of +/-15% applies within each bin. This is crucial for applications requiring uniform brightness across multiple LEDs.

3.3 Dominant Wavelength Binning

Binned at I_F = 2mA. Two bins define the color shade: AC (465.0 - 470.0 nm) and AD (470.0 - 475.0 nm), with a +/-1 nm tolerance. Bin AC produces a slightly deeper blue, while bin AD is a slightly lighter blue. This ensures color consistency in multi-LED installations.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1, Fig.6), their typical implications are analyzed here.

4.1 Luminous Intensity vs. Forward Current (I-V Curve)

The light output (luminous intensity) of an LED is not linearly proportional to current. It increases rapidly at low currents but the rate of increase typically diminishes at higher currents due to efficiency droop and thermal effects. Operating significantly above the recommended 20mA continuous current will yield diminishing returns in brightness while drastically increasing heat and reducing lifespan.

4.2 Spectral Distribution

The referenced spectral graph (Fig.1) would show a single, dominant peak centered around 468 nm (blue light) with a typical spectral half-width of 25 nm. There should be negligible emission in other parts of the visible spectrum, confirming a pure blue color output.

4.3 Viewing Angle Pattern

The polar diagram (Fig.6) illustrates the 130-degree viewing angle. The intensity is highest when looking directly at the LED (on-axis) and decreases symmetrically as the viewing angle increases, falling to 50% of the peak at +/-65 degrees from the axis.

5. Mechanical & Package Information

5.1 Package Dimensions

The LED conforms to an EIA standard chip LED footprint. Key dimensions include a typical length of 3.2mm, width of 1.6mm, and the critical height of 0.55mm. Detailed mechanical drawings specify pad positions, lens shape, and tolerances (typically ±0.10mm).

5.2 Polarity Identification

SMD LEDs have an anode (+) and cathode (-). The datasheet includes a diagram showing the polarity marking on the component body, which is essential for correct orientation during PCB assembly. Incorrect polarity will prevent the LED from illuminating and may damage it if reverse voltage is applied.

5.3 Suggested PCB Land Pattern

A recommended solder pad layout is provided to ensure a reliable solder joint, proper alignment during reflow, and adequate thermal relief. Following this pattern helps prevent tombstoning (where one end lifts off the pad) and ensures consistent soldering results.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Profile

The component is compatible with lead-free (Pb-free) solder processes. A detailed suggested reflow profile is provided, typically including: a preheat ramp to activate flux, a soak zone to evenly heat the board, a rapid temperature spike to the peak (max 260°C for ≤10 seconds), and a controlled cooling phase. Adhering to this profile, particularly the time above liquidus and peak temperature, is vital to prevent thermal damage to the LED's plastic package and internal wire bonds.

6.2 Hand Soldering Notes

If hand soldering is necessary, extreme care must be taken. The recommendation is to use a soldering iron at a maximum temperature of 300°C for no more than 3 seconds, applied only once. Excessive heat or time can melt the lens or damage the semiconductor die.

6.3 Cleaning

Only specified cleaning agents should be used. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute if cleaning is required. Harsh or unspecified chemicals can damage the plastic package, leading to cracking or clouding of the lens.

6.4 Storage & Handling

• ESD (Electrostatic Discharge) Sensitivity: LEDs are susceptible to ESD damage. Handling should be performed at an ESD-protected workstation using wrist straps and grounded equipment.
• Moisture Sensitivity: While the reel is sealed, once opened, the LEDs are exposed to ambient humidity. It is recommended to complete IR reflow within 672 hours (28 days) of opening the packaging. For longer storage out of the original bag, they should be kept in a dry cabinet or sealed container with desiccant. Components stored beyond 672 hours may require a baking cycle (e.g., 60°C for 20 hours) to remove absorbed moisture before reflow to prevent \"popcorning\" (package cracking due to vapor pressure).

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied on 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels. Standard reel quantity is 5,000 pieces. The tape uses a top cover to seal the component pockets. Packaging conforms to ANSI/EIA 481-1-A-1994 standards.

7.2 Model Number Interpretation

The part number LTST-C191TBKT-2A encodes specific attributes: LTST denotes the product family, C191 likely references the package size, TB indicates the color (Blue), KT may refer to the tape and reel packaging, and 2A could be a revision or performance code. The exact breakdown should be confirmed with the manufacturer's part numbering guide.

8. Application Recommendations

8.1 Typical Application Scenarios

• Status Indicators: Power, connectivity, or function status lights in smartphones, tablets, laptops, and wearables.
• Backlighting: Edge-lit or direct backlighting for very thin keypads, icons, or small LCD displays.
• Consumer Electronics: Decorative lighting or notification LEDs in audio equipment, gaming controllers, and smart home devices.
• Panel Indicators: Clustered indicators on industrial control panels where space is limited.

8.2 Design Considerations

• Current Limiting: Always use a series resistor or constant-current driver to limit the forward current to 20mA or less for continuous operation. The resistor value is calculated using R = (V_supply - V_F) / I_F.
• Thermal Management: Although power dissipation is low, ensuring adequate PCB copper area around the solder pads helps conduct heat away, especially in high ambient temperature environments or when driven near maximum ratings.
• Optical Design: The water-clear lens produces a focused beam. If a wider, more diffused light pattern is needed, external diffusers or light guides must be incorporated into the product design.

9. Technical Comparison & Differentiation

Compared to older LED technologies or larger packages, the LTST-C191TBKT-2A's key differentiators are its 0.55mm height and high brightness from an InGaN chip. Versus other ultra-thin LEDs, its advantages may include a standardized EIA footprint for design compatibility, specific binning options for color/brightness consistency, and clear documentation for Pb-free reflow assembly. The 130-degree viewing angle offers a good balance between a wide viewing cone and reasonable on-axis intensity.

10. Frequently Asked Questions (FAQs)

10.1 Can I drive this LED at 20mA continuously?

Yes, 20mA is the maximum recommended continuous forward current (DC). For optimal longevity and reliability, it is often advisable to operate at a slightly lower current, such as 15-18mA.

10.2 Why is there a range for Forward Voltage and Luminous Intensity?

These are inherent variations in semiconductor manufacturing. The binning system sorts LEDs into groups with similar characteristics. Designers should specify the desired bin codes when ordering to ensure uniformity in their application.

10.3 What happens if I solder it with a higher temperature or for longer than specified?

Exceeding the 260°C for 10 seconds reflow limit can cause several failures: the plastic package can deform or discolor, the internal gold wire bonds can break or intermetallic growth can weaken them, and the epoxy lens can become cloudy. Always follow the recommended profile.

10.4 Can I use this LED for reverse voltage protection or as a Zener diode?

No. The device is not designed for reverse operation. The maximum reverse voltage rating (5V for the I_R test) is for characterization only. Applying a reverse bias can immediately and catastrophically damage the LED junction.

11. Practical Design Case Study

Scenario: Designing a status indicator for a ultra-thin Bluetooth earphone case. The indicator must be blue, visible in daylight, and fit within a total cavity height of 0.8mm.

Component Selection: The LTST-C191TBKT-2A is chosen primarily for its 0.55mm height, leaving 0.25mm for the light guide/diffuser. The blue color meets the branding requirement.

Circuit Design: The case uses a 3.3V regulator. Targeting a forward current of 15mA for a balance of brightness and battery life. Using a typical V_F of 2.7V (from Bin 3), the series resistor is calculated: R = (3.3V - 2.7V) / 0.015A = 40 Ohms. A standard 39 Ohm resistor is selected.

PCB Layout: The recommended land pattern from the datasheet is used. Additional thermal relief vias are placed under the cathode pad to dissipate heat into an inner ground plane, as the device will be enclosed.

Ordering: To ensure uniform color and brightness across all production units, the order specifies bins: Luminous Intensity Bin \"L\" (brightest) and Dominant Wavelength Bin \"AD\" (preferred shade of blue).

12. Technology Principle Introduction

The LTST-C191TBKT-2A is based on InGaN (Indium Gallium Nitride) semiconductor technology. When a forward voltage is applied across the LED's p-n junction, electrons and holes are injected into the active region. They 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 InGaN material, which is engineered by adjusting the ratio of Indium to Gallium during crystal growth. A higher indium content shifts the emission towards longer wavelengths (green), while the composition used here produces blue light. The water-clear epoxy package acts as a lens, shaping the light output and providing environmental protection.

13. Industry Trends & Developments

The trend in SMD LEDs for consumer electronics continues towards further miniaturization, increased efficiency (more light output per watt of electrical input), and higher reliability. There is also a drive for tighter color consistency (smaller binning ranges) and improved performance at high temperatures. The adoption of advanced package materials to withstand higher reflow temperatures associated with lead-free soldering and double-sided assembly is standard. While this component represents a mature and optimized technology for standard blue indicators, ongoing R&D focuses on new materials like micro-LEDs and quantum dots for future display and lighting applications, which demand even smaller pixel pitches and purer colors.