LTST-C194KSKT Yellow SMD LED Datasheet - Dimensions 1.6x0.8x0.3mm - Forward Voltage 2.4V - Power 75mW - English Technical Document

1. Product Overview

The LTST-C194KSKT 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 of just 0.30 mm. This makes it an ideal choice for applications where component height is a critical design factor, such as in ultra-slim displays, mobile devices, and backlighting modules.

The device utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for its light-emitting region. This material system is known for producing high-efficiency light in the amber to red spectrum. In this specific model, it is engineered to emit yellow light. The LED is housed in a water-clear lens package, which allows for maximum light extraction and a wide viewing angle. It is packaged on industry-standard 8mm tape, supplied on 7-inch diameter reels, making it fully compatible with high-speed automated pick-and-place assembly equipment used in mass production.

1.1 Core Advantages and Target Market

The primary advantage of this LED is its combination of an ultra-thin form factor and high brightness output from the AlInGaP chip technology. Its compliance with RoHS (Restriction of Hazardous Substances) directives makes it a \"green\" product suitable for global markets with strict environmental regulations. The device is also designed to be compatible with common soldering processes, including infrared (IR) and vapor phase reflow, which are standard in surface-mount technology (SMT) assembly lines.

The target market encompasses a broad range of consumer and industrial electronics. Key applications include status indicators, backlighting for keypads and icons, panel illumination, and decorative lighting in devices where minimal thickness is paramount. Its compatibility with automatic placement equipment makes it suitable for high-volume manufacturing.

2. Technical Parameter Deep-Dive

This section provides a detailed, objective analysis of the LED's key performance parameters as defined under standard test conditions (Ta=25°C).

2.1 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 and should be avoided in circuit design.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat. Exceeding this can lead to overheating and accelerated degradation of the semiconductor junction.
• DC Forward Current (IF): 30 mA. The maximum continuous forward current that can be applied. The datasheet specifies a derating factor of 0.4 mA/°C above 25°C ambient temperature, meaning the allowable continuous current decreases as the operating environment gets hotter.
• Peak Forward Current: 80 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to briefly achieve higher light output without overheating.
• Reverse Voltage (VR): 5 V. Applying a reverse voltage greater than this can cause breakdown and irreversible damage to the LED junction.
• Operating & Storage Temperature Range: -55°C to +85°C. This defines the environmental limits for reliable operation and non-operational storage.
• Soldering Temperature Tolerance: The device can withstand wave or IR reflow soldering with a peak temperature of 260°C for 5 seconds, and vapor phase soldering at 215°C for 3 minutes.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at a forward current (IF) of 20 mA.

• Luminous Intensity (Iv): 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 assigned bin code (see Section 3). Intensity is measured using a sensor filtered to match the human eye's photopic response (CIE curve).
• Viewing Angle (2θ1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on the central axis. A wide viewing angle like this is characteristic of a water-clear, non-diffused lens, providing broad illumination.
• Peak Emission Wavelength (λP): 588 nm. This is the wavelength at which the spectral power output is highest.
• Dominant Wavelength (λd): 587.0 nm to 597.0 nm. This is the single wavelength perceived by the human eye that defines the color (yellow, in this case). It is derived from the CIE chromaticity coordinates. Units are binned within this range.
• Spectral Line Half-Width (Δλ): 15 nm. This indicates the spectral purity, measuring the width of the emission spectrum at half its maximum power. A smaller value indicates a more monochromatic light source.
• Forward Voltage (VF): Typically 2.00V, with a maximum of 2.40V at 20 mA. This is the voltage drop across the LED when operating.
• Reverse Current (IR): Maximum 10 μA when a 5V reverse bias is applied.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into \"bins\" based on key optical parameters. The LTST-C194KSKT uses a two-dimensional binning system.

3.1 Luminous Intensity Binning

LEDs are categorized into four intensity bins (N, P, Q, R) measured in millicandelas (mcd) at 20mA. Each bin has a minimum and maximum value, with a +/-15% tolerance allowed within each bin. For example, a unit in bin 'R' will have an intensity between 112.0 mcd and 180.0 mcd. Designers must account for this variation if uniform brightness across multiple LEDs is critical.

3.2 Dominant Wavelength Binning

Similarly, LEDs are binned into four wavelength groups (J, K, L, M) to control color consistency. The dominant wavelength ranges from 587.0 nm to 597.0 nm across all bins. Each specific bin (e.g., bin 'K' covers 589.5 nm to 592.0 nm) has a tighter +/- 1 nm tolerance. This ensures that all LEDs in a given batch have a very similar shade of yellow.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (Fig.1, Fig.6), their implications are standard for LED technology. Designers can expect the following general relationships:

• IV Curve (Current vs. Voltage): The forward voltage (VF) has a positive temperature coefficient and also increases slightly with higher forward current. It is non-linear, exhibiting a turn-on knee before becoming more linear.
• Luminous Intensity vs. Forward Current: Light output is approximately proportional to forward current up to a point, after which efficiency may drop due to heating effects.
• Luminous Intensity vs. Temperature: The light output of AlInGaP LEDs typically decreases as the junction temperature increases. This is a critical consideration for high-reliability or high-power drive applications.
• Spectral Distribution: The emission spectrum is centered around the peak wavelength (588 nm) with the specified 15 nm half-width, defining the yellow color point.

5. Mechanical & Packaging Information

5.1 Device Dimensions and Polarity

The LED conforms to an EIA standard package footprint. The key dimension is its height of 0.30 mm. Detailed mechanical drawings in the datasheet provide length, width, and pad spacing. The component has a polarity marking, typically a cathode indicator on the package or via the tape orientation, which must be observed during assembly to ensure correct operation.

5.2 Recommended Solder Pad Design

The datasheet includes a suggested land pattern (solder pad layout) for PCB design. Adhering to this pattern is crucial for achieving reliable solder joints and proper alignment during reflow. A note recommends a maximum stencil thickness of 0.10mm for solder paste application to prevent bridging between the closely spaced pads.

5.3 Tape and Reel Packaging Specifications

The LEDs are supplied on embossed carrier tape (8mm width) wound onto 7-inch reels. Each reel contains 5000 pieces. The packaging follows ANSI/EIA 481-1-A-1994 standards. Key specifications include: empty pockets are sealed with cover tape, a minimum packing quantity of 500 pieces for remainder reels, and a maximum of two consecutive missing components allowed per reel.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profiles

The datasheet provides two suggested infrared (IR) reflow profiles: one for standard tin-lead (SnPb) solder process and one for lead-free (Pb-free) solder process, typically using SAC (Sn-Ag-Cu) alloy. The lead-free profile requires a higher peak temperature (around 260°C) but with carefully controlled ramp-up and cooling rates to minimize thermal shock. The profiles define pre-heat zones, time above liquidus, and peak temperature duration (e.g., 5 seconds at 260°C max).

6.2 Storage and Handling Precautions

Unopened reels should be stored in an environment not exceeding 30°C and 70% relative humidity. Once removed from the original moisture-barrier bag, components should be used within 672 hours (28 days) to avoid moisture absorption, which can cause \"popcorning\" during reflow. If storage exceeds this period, a bake-out at approximately 60°C for 24 hours is recommended before soldering. For long-term storage outside the original bag, use a sealed container with desiccant or a nitrogen-purged environment.

6.3 Cleaning

If cleaning after soldering is necessary, only use specified solvents. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Unspecified chemical cleaners may damage the plastic lens or package material.

7. Application Design Considerations

7.1 Drive Circuit Design

An LED is a current-driven device. The most critical design rule is to always use a current-limiting mechanism. The datasheet strongly recommends using a series resistor for each LED (Circuit Model A), even when multiple LEDs are connected in parallel to a voltage source. This is because the forward voltage (VF) of LEDs can vary slightly from unit to unit. Without individual resistors, LEDs with a lower VF will draw disproportionately more current, leading to uneven brightness and potential overstress (Circuit Model B). For precision applications, constant current drivers are preferred.

7.2 Electrostatic Discharge (ESD) Protection

The semiconductor junction in LEDs is highly susceptible to damage from electrostatic discharge. The datasheet outlines essential ESD control measures: operators should wear grounded wrist straps or anti-static gloves; all workstations, equipment, and storage racks must be properly grounded; and an ionizer should be used to neutralize static charges that can build up on the plastic lens during handling. ESD damage may not cause immediate failure but can lead to reduced lifetime or erratic performance.

7.3 Thermal Management

Although a small device, the 75mW power dissipation limit and the current derating curve indicate that thermal management is important, especially in high-ambient-temperature environments or when driving near the maximum continuous current. Ensuring adequate PCB copper area around the solder pads can help dissipate heat. The luminous intensity and dominant wavelength can shift with junction temperature, so maintaining a stable thermal environment contributes to consistent optical performance.

8. Technical Comparison and Differentiation

The primary differentiator of the LTST-C194KSKT is its 0.30mm profile within the AlInGaP yellow LED category. Compared to standard SMD LEDs which are often 0.6mm or 1.0mm tall, this represents a 50-70% reduction in height. This is achieved without a significant compromise on optical performance, as it still offers a wide viewing angle and brightness levels suitable for indicator applications. Its compatibility with standard reflow processes makes it a drop-in replacement for thicker components in space-upgrade scenarios, unlike some ultra-thin devices that require specialized assembly techniques.

9. 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. For example, with a 3.3V supply and a typical VF of 2.0V at 20mA, the resistor value would be R = (3.3V - 2.0V) / 0.02A = 65 Ohms. A standard 68 Ohm resistor would be suitable.

Q: Why is there such a large range in luminous intensity (28 to 180 mcd)?
A: This is the total range across all production. For a specific order, you can request a tighter bin (e.g., Bin R: 112-180 mcd) to ensure brightness consistency in your application.

Q: Is the water-clear lens suitable for a wide, uniform light bar?
A: The water-clear lens provides a wide viewing angle (130°) but may produce a more focused \"hot spot\" compared to a diffused lens. For perfectly uniform bars, secondary optics or light guides are often used in conjunction with the LEDs.

Q: How do I interpret the soldering profile graph?
A: The graph shows temperature on the Y-axis and time on the X-axis. The line defines the target temperature the LED package should experience as it travels through the reflow oven. Key points are the maximum ramp-up rate, pre-heat soak temperature and duration, time above the solder's melting point, peak temperature, and maximum cooling rate.

10. Practical Design and Usage Examples

Example 1: Status Indicator in a Wearable Device
In a smartwatch or fitness tracker, board real estate and thickness are severely limited. A single LTST-C194KSKT, driven at 10-15 mA via a GPIO pin and a series resistor, can provide a clear notification (charging, message, low battery) without adding meaningful thickness. Its wide viewing angle ensures the light is visible from various angles on the wrist.

Example 2: Backlighting for Membrane Switch Panels
For industrial control panels with membrane keypads, multiple yellow LEDs can be placed beneath translucent key icons. The ultra-thin profile allows them to fit into the shallow cavity behind the membrane sheet. By specifying LEDs from the same intensity and wavelength bin (e.g., Bin Q, Bin K), consistent color and brightness across all keys can be achieved.

Example 3: Decorative Edge Lighting
In a thin consumer electronics product (e.g., a speaker, router), a line of these LEDs placed along an internal edge, coupled with a light guide or diffuser, can create a uniform glowing accent line. The 0.3mm height allows them to be placed extremely close to the product's outer shell.

11. Operating Principle Introduction

Light emission in the LTST-C194KSKT is based on electroluminescence in a semiconductor p-n junction made of AlInGaP materials. When a forward voltage exceeding the junction's built-in potential is applied, electrons from the n-type region and holes from the p-type region are injected into the active region where they recombine. In a direct bandgap semiconductor like AlInGaP, this recombination event releases energy in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material, which is engineered during the crystal growth process to be in the yellow spectrum (~588-597 nm). The water-clear epoxy lens encapsulates the chip, provides mechanical protection, and shapes the light output pattern.

12. Technology Trends and Context

The development of the LTST-C194KSKT aligns with several key trends in optoelectronics and electronics manufacturing. The push for miniaturization and lower profile components is relentless, driven by consumer demand for thinner smartphones, tablets, and wearables. AlInGaP technology remains the dominant solution for high-efficiency amber, yellow, and red LEDs, though advancements in phosphor-converted blue LEDs (pc-LEDs) now offer alternatives for some yellow/green applications. The emphasis on RoHS compliance and green manufacturing is now a universal standard. Furthermore, the detailed binning systems and standardized packaging (tape & reel, EIA footprints) reflect the industry's need for high-volume, automated, and consistent production to meet the demands of global supply chains. The inclusion of specific profiles for lead-free soldering underscores the industry's complete transition away from lead-based processes.