SMD LED LTST-C191TGKT Datasheet - Super Thin 0.55mm - InGaN Green - 3.6V Max - 76mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for the LTST-C191TGKT, a surface-mount device (SMD) LED lamp. Designed for automated printed circuit board (PCB) assembly, this component is ideal for space-constrained applications across a broad spectrum of electronic equipment.

1.1 Core Advantages and Target Market

The primary advantages of this LED include its exceptionally thin profile of 0.55mm, which enables integration into ultra-slim devices. It utilizes an ultra-bright InGaN (Indium Gallium Nitride) semiconductor chip to produce green light. The device is fully compliant with the Restriction of Hazardous Substances (RoHS) directive. Its packaging is standardized on 8mm tape wound onto 7-inch diameter reels, conforming to EIA standards, making it fully compatible with high-speed automatic pick-and-place equipment and standard infrared (IR) reflow soldering processes. The target markets are diverse, encompassing telecommunications equipment (cordless and cellular phones), portable computing (notebook computers), network infrastructure, home appliances, and indoor signage or display applications.

1.2 Key Applications

• Backlighting for keypads and keyboards.
• Status and power indicators in consumer and industrial electronics.
• Micro-displays and icon illumination.
• Signal and symbolic lighting in control panels and instrumentation.

2. Package and Mechanical Dimensions

The LTST-C191TGKT features a water-clear lens encapsulating an InGaN green light-emitting chip. All critical package dimensions are provided in the datasheet drawings with a standard tolerance of ±0.1mm (±0.004 inches) unless otherwise specified. The super-low height is a defining mechanical characteristic.

3. Absolute Maximum Ratings and Characteristics

All ratings are specified at an ambient temperature (Ta) of 25°C. Exceeding these limits may cause permanent damage to the device.

3.1 Absolute Maximum Ratings

• Power Dissipation (Pd): 76 mW. This is the maximum amount of power the device can safely dissipate as heat.
• Peak Forward Current (I_F(PEAK)): 100 mA. This is the maximum instantaneous current, permissible only under pulsed conditions with a 1/10 duty cycle and a pulse width of 0.1ms.
• Continuous Forward Current (I_F): 20 mA. This is the maximum recommended current for continuous DC operation.
• Operating Temperature Range: -20°C to +80°C. The device is designed to function within this environmental temperature range.
• Storage Temperature Range: -30°C to +100°C.
• Infrared Reflow Soldering Condition: Withstands a peak temperature of 260°C for a maximum of 10 seconds, which is critical for lead-free (Pb-free) assembly processes.

3.2 Recommended IR Reflow Profile for Pb-Free Process

The datasheet includes a detailed temperature vs. time graph outlining the suggested reflow soldering profile. Key parameters include a pre-heat stage up to 150-200°C, a maximum pre-heat time of 120 seconds, a peak temperature not exceeding 260°C, and a time above 260°C limited to a maximum of 10 seconds. The profile is based on JEDEC standards to ensure reliable soldering without thermal damage to the LED package.

3.3 Electrical and Optical Characteristics

These are the typical performance parameters measured at Ta=25°C and I_F=20mA, unless noted.

• Luminous Intensity (I_V): 71 - 450 mcd (millicandela). Measured using a sensor filtered to match the CIE photopic eye-response curve.
• Viewing Angle (2θ_1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its axial (on-center) value, indicating a very wide viewing cone.
• Peak Emission Wavelength (λ_P): 530 nm (nanometers). The wavelength at which the spectral output is strongest.
• Dominant Wavelength (λ_d): 520 - 535 nm. This is the single wavelength perceived by the human eye that defines the color (green) of the LED, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): 35 nm. The bandwidth of the emitted light spectrum at half its maximum intensity.
• Forward Voltage (V_F): 2.8V - 3.6V. The voltage drop across the LED when operating at 20mA.
• Reverse Current (I_R): 10 μA (max) at a Reverse Voltage (V_R) of 10V. Important Note: The device is not designed for operation under reverse bias; this test condition is for informational purposes only.

4. Bin Rank and Classification System

To ensure color and brightness consistency in production, LEDs are sorted into bins based on key parameters. The bin code is part of the ordering information.

4.1 Forward Voltage (V_F) Rank

Binned at I_F=20mA. Tolerance per bin is ±0.1V.
Bin Codes: D7 (2.80-3.00V), D8 (3.00-3.20V), D9 (3.20-3.40V), D10 (3.40-3.60V).

4.2 Luminous Intensity (I_V) Rank

Binned at I_F=20mA. Tolerance per bin is ±15%.
Bin Codes: Q (71.0-112.0 mcd), R (112.0-180.0 mcd), S (180.0-280.0 mcd), T (280.0-450.0 mcd).

4.3 Hue (Dominant Wavelength) Rank

Binned at I_F=20mA. Tolerance per bin is ±1 nm.
Bin Codes: AP (520.0-525.0 nm), AQ (525.0-530.0 nm), AR (530.0-535.0 nm).

5. Typical Performance Curves Analysis

The datasheet provides graphical representations of key relationships, essential for circuit design.

• Relative Luminous Intensity vs. Forward Current: Shows how light output increases with current, typically in a sub-linear manner, highlighting the importance of current regulation over voltage driving.
• Forward Voltage vs. Forward Current: Illustrates the diode's I-V characteristic, crucial for calculating series resistor values or designing constant-current drivers.
• Relative Luminous Intensity vs. Ambient Temperature: Demonstrates the thermal derating of light output, which decreases as junction temperature rises.
• Spectral Distribution: A graph plotting relative intensity against wavelength, showing the peak at ~530nm and the 35nm half-width, confirming the pure green color emission.

6. Assembly, Handling, and Storage Guidelines

6.1 PCB Attachment Pad Layout

A recommended land pattern (footprint) for the PCB is provided, including dimensions for the solder pads. Adhering to this design ensures proper soldering, alignment, and thermal management during reflow.

6.2 Cleaning

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

6.3 ESD (Electrostatic Discharge) Precautions

LEDs are sensitive to static electricity and voltage surges. It is strongly recommended to use a grounded wrist strap or anti-static gloves when handling. All equipment, including workstations and soldering irons, must be properly grounded to prevent damage.

6.4 Storage Conditions

• Sealed Package: Store at ≤30°C and ≤90% Relative Humidity (RH). The shelf life in the original moisture-proof bag with desiccant is one year.
• Opened Package: For components removed from their original packaging, the storage environment must not exceed 30°C / 60% RH. It is recommended to complete IR reflow soldering within 672 hours (28 days, MSL 2a level). For storage beyond this period, components should be kept in a sealed container with desiccant or in a nitrogen atmosphere. Components stored out of bag for more than 672 hours require baking at approximately 60°C for at least 20 hours before assembly to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.5 Soldering Methods

Reflow Soldering: Follow the profile in section 3.2. Peak temperature 260°C max, time above 260°C limited to 10 seconds max. A maximum of two reflow cycles is permitted.
Hand Soldering (Iron): Use a temperature-controlled iron set to a maximum of 300°C. Contact time should be limited to 3 seconds per solder joint. Hand soldering should be performed only once.

7. Packaging and Tape & Reel Specifications

The LEDs are supplied in embossed carrier tape with a protective cover tape. The tape width is 8mm. Reels have a standard diameter of 7 inches (178mm) and contain 5000 pieces per full reel. A minimum order quantity of 500 pieces applies for partial reels. The packaging conforms to ANSI/EIA-481 specifications. Detailed dimensional drawings for the tape pockets and the reel are provided, including hub diameter, flange diameter, and reel width.

8. Application Notes and Design Considerations

8.1 Intended Use and Reliability Disclaimer

This LED is designed for use in standard commercial and consumer electronic equipment. For applications requiring exceptional reliability where failure could jeopardize life or health (e.g., aviation, medical life-support, transportation safety systems), specific consultation and qualification are required prior to design-in.

8.2 Driving the LED

To ensure stable light output and long lifetime, drive the LED with a constant current source, not a constant voltage. The recommended continuous current is 20mA. A simple series current-limiting resistor can be used with a voltage source, calculated as R = (V_supply - V_F) / I_F, where V_F should be chosen from the typical or maximum value from the binning table to ensure I_F does not exceed 20mA under worst-case conditions.

8.3 Thermal Management

Although the power dissipation is low (76mW max), proper thermal design on the PCB is important. The recommended solder pad design also acts as a heat sink. Ensuring a good thermal path away from the LED junction helps maintain luminous intensity and longevity, especially in high ambient temperature environments or when driven near maximum ratings.

8.4 Optical Design

The wide 130-degree viewing angle makes this LED suitable for applications requiring broad illumination or visibility from many angles. For focused or directed light, external lenses or light guides may be necessary. The water-clear lens provides a neutral base for potential secondary optical elements.

9. Technical Comparison and Differentiation

The primary differentiator of the LTST-C191TGKT is its combination of an ultra-thin 0.55mm profile with high brightness from an InGaN chip. Compared to older technology like AlGaInP, InGaN offers superior efficiency and color purity for green wavelengths. The RoHS compliance and compatibility with standard, high-volume Pb-free reflow processes make it a modern, environmentally friendly choice suitable for global markets. The comprehensive binning system allows designers to select the precise brightness and color point required for their application, ensuring visual consistency in end products.

10. Frequently Asked Questions (FAQ)

Q: What is the difference between Peak Wavelength and Dominant Wavelength?
A: Peak Wavelength (λ_P) is the physical wavelength where the LED emits the most optical power. Dominant Wavelength (λ_d) is a calculated value based on human color perception (CIE chart) that defines the perceived color. For monochromatic LEDs like this green one, they are typically close but not identical.

Q: Can I drive this LED with a 5V supply and a resistor?
A: Yes. Using the maximum V_F of 3.6V to ensure safe current under all conditions: R = (5V - 3.6V) / 0.020A = 70 Ohms. A standard 68 or 75 Ohm resistor would be appropriate. Always verify the actual current in the circuit.

Q: Why is the storage condition for opened packages so strict (672 hours)?
A> SMD packages can absorb moisture from the air. During the high heat of reflow soldering, this trapped moisture can vaporize rapidly, causing internal delamination or cracking (\"popcorning\"). The 672-hour limit and baking procedure are defined by the component's Moisture Sensitivity Level (MSL 2a) to prevent this failure mode.

Q: Is this LED suitable for automotive interior lighting?
A> While it meets basic technical specs, automotive applications typically require components qualified to specific automotive-grade standards (like AEC-Q102) for temperature cycling, humidity, and long-term reliability. This datasheet does not claim such qualifications, so consultation for the specific application is necessary.

11. Design-in Case Study Example

Scenario: Designing a status indicator for a portable Bluetooth speaker. The indicator needs to be visible in daylight, have a consistent green color, and fit within a very thin enclosure.

Selection Rationale: The LTST-C191TGKT is chosen for its 0.55mm height, allowing it to fit behind a thin diffuser. The high brightness (up to 450 mcd) ensures visibility. To guarantee a specific shade of green across all production units, the designer specifies bin code \"AQ\" (525-530nm Dominant Wavelength) and bin code \"S\" (180-280 mcd) during procurement.

Circuit Design: The speaker's main board has a 3.3V rail. Using a typical V_F of 3.2V (from bin D8), a series resistor is calculated: R = (3.3V - 3.2V) / 0.020A = 5 Ohms. A 5.1 Ohm resistor is selected. The LED anode is connected to the 3.3V rail via the resistor, and the cathode is switched to ground by a microcontroller GPIO pin configured as an open-drain output.

Layout: The recommended PCB pad layout is followed precisely. The ground pad is connected to a small copper pour to aid in heat dissipation, even though the power is low.

12. Technology Introduction and Trends

InGaN Technology: Indium Gallium Nitride is a III-V semiconductor compound whose bandgap can be tuned by adjusting the ratio of Indium to Gallium. This allows the production of LEDs emitting light from ultraviolet through blue and green spectra. InGaN-based LEDs are known for high efficiency and brightness.

Industry Trends: The trend in SMD LEDs for consumer electronics is continuously towards smaller package sizes, lower profiles, higher luminous efficacy (more light per watt), and tighter color consistency. There is also a strong drive for higher reliability to meet the demands of automotive and industrial applications. The move to Pb-free soldering and RoHS compliance is now a universal standard. Future developments may involve even thinner chip-scale packages (CSP) and integrated driver circuits within the LED package.