LTST-C191TBKT Blue SMD LED Datasheet - Dimensions 3.2x1.6x0.55mm - Voltage 2.8-3.8V - Power 76mW - English Technical Documentation

1. Product Overview

The LTST-C191TBKT is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, space-constrained electronic applications. It belongs to a category of ultra-thin chip LEDs, featuring a remarkably low profile of just 0.55 mm. This makes it an ideal choice for backlighting in slim consumer electronics, indicator lights in portable devices, and status displays where vertical space is at a premium. The device utilizes an InGaN (Indium Gallium Nitride) semiconductor chip, which is the industry standard for producing high-efficiency blue light. It is packaged on 8mm tape and supplied on standard 7-inch diameter reels, making it fully compatible with high-speed automated pick-and-place assembly equipment used in volume manufacturing.

1.1 Core Features and Advantages

The primary advantages of this LED stem from its physical and electrical design. The most notable feature is its ultra-thin 0.55 mm height, which directly addresses the trend towards thinner end products. It is classified as a green product and complies with RoHS (Restriction of Hazardous Substances) directives, ensuring it meets international environmental standards. The InGaN chip technology provides high luminous intensity from a small source. Its EIA (Electronic Industries Alliance) standard package footprint ensures compatibility with a wide range of existing PCB (Printed Circuit Board) layouts and design libraries. Furthermore, it is designed to be compatible with standard infrared (IR) reflow soldering processes, which is the dominant method for attaching SMD components, simplifying the manufacturing workflow.

2. Technical Specifications: In-Depth Analysis

This section provides a detailed breakdown of the device's absolute limits and operational characteristics, which are critical for reliable circuit design.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are not intended for normal operation. The maximum continuous DC forward current (I_F) is 20 mA. Under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width, a higher peak forward current of 100 mA is permissible. The total power dissipation must not exceed 76 mW, a limit dictated by the package's ability to transfer heat to the PCB. The device is rated for an operating temperature range of -20°C to +80°C and can be stored in environments from -30°C to +100°C. For assembly, it can withstand a peak infrared reflow soldering temperature of 260°C for a maximum of 10 seconds.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard ambient temperature (T_a) of 25°C and a forward current of 20 mA, unless otherwise specified. They define the device's performance under normal operating conditions.

• Luminous Intensity (I_V): Ranges from a minimum of 28.0 mcd to a maximum of 180.0 mcd. The actual value for a specific unit depends on its bin code (see Section 3). Intensity is measured using a sensor filtered to match the photopic (human eye) response curve.
• Viewing Angle (2θ_1/2): A wide 130-degree angle, defined as the off-axis point where luminous intensity drops to half its on-axis (0°) value. This indicates a Lambertian or near-Lambertian emission pattern, suitable for applications requiring wide-area illumination rather than a focused beam.
• Peak Wavelength (λ_P): Typically 468 nm. This is the wavelength at which the spectral power distribution is at its maximum.
• Dominant Wavelength (λ_d): Ranges from 465.0 nm to 475.0 nm. This is the single wavelength perceived by the human eye to match the LED's color, derived from the CIE chromaticity diagram. It is the key parameter for color consistency.
• Spectral Line Half-Width (Δλ): Approximately 25 nm. This measures the bandwidth of the emitted light, indicating the spectral purity. A typical value for a blue InGaN LED.
• Forward Voltage (V_F): Ranges from 2.80 V to 3.80 V at 20 mA. The exact value is binned (see Section 3). This parameter is crucial for designing the current-limiting circuitry.
• Reverse Current (I_R): Maximum of 10 μA when a reverse voltage (V_R) of 5V is applied. It is critical to note that this LED is not designed for reverse operation; this test condition is for characterization only. Applying reverse bias in circuit could damage the device.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-C191TBKT uses a three-dimensional binning system for key parameters.

3.1 Forward Voltage Binning

Units are sorted into bins D7 through D11 based on their forward voltage (V_F) at 20 mA. For example, bin D7 contains LEDs with V_F between 2.80V and 3.00V, while bin D11 contains those from 3.60V to 3.80V. The tolerance within each bin is ±0.1V. Selecting LEDs from the same voltage bin helps maintain uniform brightness and power consumption in an array.

3.2 Luminous Intensity Binning

Intensity is binned into codes N, P, Q, and R. Bin N covers 28.0-45.0 mcd, and bin R covers the highest range of 112.0-180.0 mcd. The tolerance for each intensity bin is ±15%. This allows designers to choose a brightness level appropriate for their application, balancing visibility with power efficiency.

3.3 Dominant Wavelength Binning

The color (dominant wavelength) is binned into two codes: AC (465.0-470.0 nm) and AD (470.0-475.0 nm), with a ±1 nm tolerance per bin. This tight control ensures minimal color variation, which is essential for applications like multi-LED backlighting or status indicators where color matching is important.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Figure 1 for spectral distribution, Figure 6 for viewing angle), their implications are standard for InGaN LEDs. The forward current vs. forward voltage (I-V) curve would show the typical exponential relationship, with the knee voltage around 2.8-3.0V. The luminous intensity vs. forward current curve is generally linear up to the rated current, after which efficiency may drop due to heating. The dominant wavelength typically has a slight negative temperature coefficient, meaning it may shift to longer wavelengths (slightly more green) as the junction temperature increases. The wide 130-degree viewing angle curve confirms a near-Lambertian emission profile.

5. Mechanical and Package Information

5.1 Physical Dimensions

The package follows an EIA standard footprint. Key dimensions include a typical length of 3.2 mm, width of 1.6 mm, and the defining height of 0.55 mm. Detailed dimensioned drawings are provided in the datasheet for PCB land pattern design. All dimensions have a standard tolerance of ±0.10 mm unless otherwise specified.

5.2 Polarity Identification and Pad Design

The LED has an anode and cathode. Polarity is typically indicated by a marking on the package or by an asymmetric feature in the footprint. The datasheet includes suggested soldering pad dimensions to ensure a reliable solder fillet forms during reflow, which is critical for both electrical connection and mechanical strength. Proper pad design also aids in heat dissipation.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

The device is qualified for lead-free (Pb-free) solder processes. A suggested infrared reflow profile is provided, compliant with JEDEC standards. Key parameters include a pre-heat zone (typically 150-200°C), a controlled ramp to a peak temperature not exceeding 260°C, and a time above liquidus (TAL) appropriate for the solder paste. The peak temperature of 260°C must not be exceeded for more than 10 seconds. It is emphasized that the exact profile must be characterized for the specific PCB design, components, and solder paste used.

6.2 Manual Soldering

If manual soldering with an iron is necessary, the recommendation is to use a tip temperature not exceeding 300°C and to limit contact time to a maximum of 3 seconds for a single operation only. Excessive heat from a soldering iron can easily damage the small package.

6.3 Storage and Handling Conditions

The LEDs are moisture-sensitive. When stored in their original sealed moisture-proof bag with desiccant, they should be kept at ≤30°C and ≤90% RH and used within one year. Once the bag is opened, the storage environment should not exceed 30°C and 60% RH. Components exposed to ambient humidity for more than 672 hours (28 days) should be baked at approximately 60°C for at least 20 hours before reflow soldering to prevent popcorning (package cracking due to vapor pressure). For extended storage out of the original bag, use a sealed container with desiccant.

6.4 Cleaning

If cleaning after soldering is required, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is recommended. Unspecified chemical cleaners may damage the plastic package material.

7. Packaging and Ordering Information

The standard packaging is 8mm wide embossed carrier tape on 7-inch (178 mm) diameter reels. Each reel contains 5000 pieces of the LTST-C191TBKT LED. The tape uses a top cover to seal empty pockets. Packaging follows ANSI/EIA 481-1-A-1994 specifications. For production remnants, a minimum packing quantity of 500 pieces applies.

8. Application Suggestions

8.1 Typical Application Scenarios

The ultra-thin profile makes this LED ideal for: backlighting keys on slim keyboards or remote controls, status indicators in smartphones, tablets, and ultra-thin laptops, panel illumination in automotive dashboards or consumer appliances, and as a general-purpose blue indicator in densely packed PCBs.

8.2 Design Considerations and Notes

• Current Driving: An LED is a current-driven device. Always use a series current-limiting resistor or a constant-current driver circuit. The resistor value is calculated using R = (V_supply - V_F) / I_F. Use the maximum V_F from the bin or datasheet to ensure current does not exceed 20 mA under worst-case conditions.
• ESD Protection: The InGaN chip is sensitive to electrostatic discharge (ESD). Proper ESD controls (wrist straps, grounded workstations, conductive flooring) must be used during handling and assembly.
• Thermal Management: While the power is low, ensuring a good thermal path from the LED pads to the PCB copper helps maintain performance and longevity, especially when driven at or near the maximum current.
• Reverse Voltage Protection: As the device is not designed for reverse bias, consider adding a protection diode in parallel (cathode to anode) if the LED could be exposed to reverse voltage in the circuit.

9. Technical Comparison and Differentiation

The primary differentiator of the LTST-C191TBKT is its 0.55 mm height, which is thinner than many standard SMD LEDs (e.g., 0603 or 0402 packages which are often >0.8 mm tall). Compared to side-view LEDs, it offers a top-emitting format with a wide viewing angle. Its InGaN technology provides higher efficiency and better color saturation than older blue LED technologies. The comprehensive binning system offers better color and brightness consistency compared to unbinned or loosely binned alternatives, which is critical for multi-LED applications.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: What resistor do I need for a 5V supply?
A: Using the maximum V_F of 3.8V and target I_F of 20mA: R = (5V - 3.8V) / 0.02A = 60 Ω. A standard 62 Ω or 68 Ω resistor would be suitable. Always verify with the actual V_F bin of your LEDs.

Q: Can I drive it with a 3.3V supply?
A: Possibly, but carefully. If the LED's V_F is at the high end of its range (e.g., 3.8V), a 3.3V supply may not turn it on fully or at all. You would need to check the minimum V_F (2.8V) and likely use a constant-current driver instead of a simple resistor for reliable operation.

Q: How do I interpret the luminous intensity value?
A: Luminous intensity (mcd) measures brightness in a specific direction (on-axis). The wide viewing angle means this brightness is spread over a large area, so the perceived brightness on a surface depends on distance and angle. For comparison, a typical 5mm through-hole LED might be 1000-5000 mcd but with a much narrower beam.

Q: Is it suitable for outdoor use?
A: The operating temperature range (-20°C to +80°C) covers many outdoor conditions. However, prolonged exposure to direct sunlight (UV) and weather may degrade the plastic package. For harsh environments, confirm suitability with the manufacturer and consider protective coatings.

11. Practical Design and Usage Examples

Example 1: Multi-LED Status Bar: Designing a bar graph with 10 blue LEDs. To ensure uniform appearance, specify LEDs from the same Dominant Wavelength bin (e.g., all AD bin) and the same Luminous Intensity bin (e.g., all P bin). Drive them with a single constant-current source shared via transistors or an LED driver IC to guarantee identical current and thus identical brightness and color.

Example 2: Backlighting a Thin Membrane Switch: The 0.55mm height allows the LED to fit behind a membrane layer and a diffuser in an assembly less than 2mm thick. The wide 130-degree viewing angle ensures even illumination of the switch icon. A current of 10-15 mA (instead of 20 mA) might be sufficient, reducing power consumption and heat.

12. Technology Principle Introduction

The LTST-C191TBKT is based on InGaN semiconductor technology. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region. Their recombination releases energy in the form of photons (light). The specific composition of the Indium Gallium Nitride alloy in the quantum well structure determines the bandgap energy, and thus the wavelength (color) of the emitted light. For blue light, a bandgap corresponding to approximately 2.6-2.7 electron volts (eV) is required. The plastic package serves to protect the fragile semiconductor die, provide a mechanical structure, and incorporates a lens that shapes the light output, resulting in the wide viewing angle.

13. Industry Trends and Developments

The trend in SMD LEDs for consumer electronics continues towards miniaturization (smaller footprints and lower profiles) and higher efficiency (more light output per watt of electrical input). There is also a drive for improved color consistency and tighter binning from manufacturers. The adoption of lead-free and halogen-free materials for environmental compliance is standard. In terms of application, integration is key, with LEDs increasingly being co-packaged with drivers or sensors, or embedded directly into PCBs. The underlying InGaN technology is mature but continues to see incremental improvements in internal quantum efficiency and longevity.