LTST-C194KRKT SMD LED Datasheet - Dimensions 1.6x0.8x0.3mm - Voltage 2.4V - Power 75mW - Red Color - English Technical Document

1. Product Overview

The LTST-C194KRKT is a surface-mount device (SMD) light-emitting diode (LED) belonging to the chip LED category. Its primary defining characteristic is an exceptionally low profile, with a height of only 0.30 millimeters. This makes it suitable for applications where space constraints, particularly in the Z-axis, are critical. The device utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce red light, encapsulated in a water-clear lens package. It is designed for compatibility with modern, high-volume electronic assembly processes.

1.1 Core Advantages and Target Market

The core advantages of this LED stem from its form factor and process compatibility. The extra-thin design enables integration into slim consumer electronics such as mobile devices, ultra-thin displays, and wearable technology. Its packaging on 8mm tape wound onto 7-inch reels aligns with automated pick-and-place equipment standards, facilitating efficient assembly. Furthermore, compliance with infrared (IR) reflow soldering processes allows it to be mounted alongside other SMD components in a single reflow cycle, which is the industry standard for PCB assembly. The device is also specified as a RoHS-compliant green product, meeting environmental regulations. The target market includes manufacturers of consumer electronics, indicators, backlighting for keypads or icons, and any application requiring a reliable, low-profile red indicator.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters specified for the LTST-C194KRKT LED.

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.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat under any condition. 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 typical operating condition for testing optical parameters is 20 mA, providing a 10 mA safety margin.
• Peak Forward Current: 80 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). Pulsing allows for higher instantaneous brightness without exceeding the average power dissipation limit.
• Reverse Voltage (VR): 5 V. LEDs are not designed to withstand high reverse voltages. Exceeding 5V in reverse bias can cause a breakdown of the PN junction.
• Operating & Storage Temperature: -30°C to +85°C / -40°C to +85°C. These ranges define the environmental conditions for reliable operation and non-operational storage, respectively.

2.2 Electro-Optical Characteristics

Measured at Ta=25°C and IF=20mA, these parameters define the device's performance under standard test conditions.

• Luminous Intensity (Iv): Ranges from a minimum of 11.2 mcd to a maximum of 180.0 mcd. The wide range is managed through a binning system (detailed in Section 3). Intensity is measured using a sensor filtered to match the photopic (human eye) response curve (CIE).
• Viewing Angle (2θ1/2): 130 degrees. This is a very wide viewing angle, typical for a chip LED with a water-clear lens. The angle is defined as the point where luminous intensity drops to half of its on-axis (0°) value.
• Peak Wavelength (λP): 639 nm. This is the wavelength at which the spectral power output is highest. It is a physical measurement of the emitted light.
• Dominant Wavelength (λd): 631 nm. This is a calculated value derived from the CIE chromaticity diagram and represents the perceived color of the light. The difference between peak and dominant wavelength is due to the shape of the emission spectrum.
• Spectral Line Half-Width (Δλ): 20 nm. This indicates the spectral purity or bandwidth of the emitted light. A value of 20 nm is typical for a red AlInGaP LED, resulting in a saturated red color.
• Forward Voltage (VF): 2.4 V (typical). This is the voltage drop across the LED when driven at 20 mA. It is a critical parameter for designing the current-limiting circuitry.
• Reverse Current (IR): 10 μA (max). The small leakage current when 5V is applied in reverse bias.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-C194KRKT uses a binning system for luminous intensity.

3.1 Luminous Intensity Binning

The bin codes (L, M, N, P, Q, R) categorize LEDs based on their measured luminous intensity at 20 mA. Each bin has a minimum and maximum value, and a tolerance of +/-15% is applied within each bin. For example, Bin 'L' covers 11.2 to 18.0 mcd, while Bin 'R' covers 112.0 to 180.0 mcd. This allows designers to select a bin that meets their specific brightness requirements, ensuring visual consistency within an assembly. The datasheet does not indicate binning for dominant wavelength or forward voltage for this specific part number, suggesting these parameters are tightly controlled during manufacturing.

4. Performance Curve Analysis

While the provided PDF excerpt mentions typical curves, the specific graphs (e.g., IV curve, temperature vs. intensity, spectral distribution) are not included in the text. Based on standard LED behavior and the given parameters, we can infer the general shape of these curves.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The I-V characteristic of an LED is exponential. For the LTST-C194KRKT, with a typical VF of 2.4V at 20mA, the curve will show a very low current below approximately 1.8V (the turn-on voltage). The current will then rise sharply with a small increase in voltage. This non-linear relationship is why LEDs must be driven by a current source or via a current-limiting resistor, not a constant voltage source.

4.2 Temperature Characteristics

LED performance is temperature-dependent. Typically, the forward voltage (VF) has a negative temperature coefficient, decreasing by about 2 mV/°C. Luminous intensity (Iv) also decreases as junction temperature rises. The specified operating temperature up to 85°C ambient means the designer must consider thermal management, especially if operating at or near the maximum DC current, to maintain performance and longevity.

4.3 Spectral Distribution

The emission spectrum for an AlInGaP red LED is a bell-shaped curve centered around the peak wavelength of 639 nm, with a half-width of 20 nm. This results in a pure, saturated red color. The dominant wavelength (631 nm) will be slightly shorter than the peak due to the shape of the CIE eye sensitivity curve, which weights different wavelengths differently.

5. Mechanical and Packaging Information

5.1 Package Dimensions and Polarity

The LED conforms to an EIA standard package outline. The key dimension is the height of 0.30 mm. The footprint dimensions (length and width) are typical for a chip LED. The polarity is indicated on the device itself (typically a cathode mark, such as a green line, a notch, or a different-sized pad on the underside). The PCB layout must match this polarity to ensure correct orientation during automated assembly and operation.

5.2 Recommended Solder Pad Design

The datasheet includes a suggested land pattern (solder pad dimensions) for PCB design. Adhering to this pattern is crucial for achieving reliable solder joints during reflow. It ensures proper wetting, alignment, and mechanical strength. The note recommends a maximum stencil thickness of 0.10mm for solder paste application, which controls the volume of paste deposited and prevents solder bridging.

6. Soldering and Assembly Guidelines

6.1 Infrared Reflow Soldering Profile

The device is fully compatible with lead-free (Pb-free) IR reflow processes. A suggested profile is provided, which typically follows a JEDEC-standard reflow curve. Key parameters include: a pre-heat zone (150-200°C), a controlled ramp to a peak temperature not exceeding 260°C, and a time above liquidus (TAL) to ensure proper solder joint formation. The critical specification is that the LED body must not be exposed to 260°C for more than 10 seconds. This profile must be characterized for the specific PCB, oven, and other components used in assembly.

6.2 Storage and Handling Conditions

LEDs are moisture-sensitive devices (MSD). When sealed in their original moisture-proof bag with desiccant, they have a shelf life of one year when stored at ≤30°C and ≤90% RH. Once the bag is opened, the exposure time to ambient factory conditions (≤30°C, ≤60% RH) is limited to 672 hours (28 days) before they must be soldered. If this time is exceeded, a bake-out at 60°C for at least 20 hours is required to remove absorbed moisture and prevent \"popcorning\" (package cracking) during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Harsh or unspecified chemicals can damage the plastic lens or package.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The LEDs are supplied in embossed carrier tape with a cover tape, wound onto 7-inch (178 mm) diameter reels. Each reel contains 5000 pieces. The tape dimensions and pocket spacing conform to ANSI/EIA 481-1-A-1994 standards, ensuring compatibility with standard automated feeders. The specification allows for a maximum of two consecutive empty pockets on a reel.

8. Application Design Recommendations

8.1 Drive Circuit Design

An LED is a current-driven device. The most reliable method to drive multiple LEDs is to use a separate current-limiting resistor in series with each LED (Circuit A in the datasheet). This compensates for the natural variation in forward voltage (VF) from one LED to another. Connecting multiple LEDs directly in parallel with a single shared resistor (Circuit B) is not recommended, as the LED with the lowest VF will draw more current, leading to uneven brightness and potential overstress.

8.2 Electrostatic Discharge (ESD) Protection

Although not detailed in the excerpt, AlInGaP LEDs are generally sensitive to electrostatic discharge. Standard ESD handling precautions should be observed during assembly: use grounded workstations, wrist straps, and conductive containers.

8.3 Application Scope and Limitations

The LED is designed for general-purpose electronic equipment. For applications requiring exceptional reliability where failure could risk safety (e.g., aviation, medical devices, transportation controls), a more rigorous component qualification and application-specific consultation would be necessary. The device's specifications are validated for standard commercial environments.

9. Technical Comparison and Differentiation

The primary differentiation of the LTST-C194KRKT is its ultra-low 0.3mm profile. Compared to standard SMD LEDs (e.g., 0603 or 0402 packages which are often 0.6-0.8mm tall), this device enables thinner product designs. The use of AlInGaP technology provides higher efficiency and better temperature stability for red light compared to older technologies like GaAsP. The water-clear lens, combined with the wide 130-degree viewing angle, offers a broad, even illumination pattern suitable for indicator and backlight applications where visibility from multiple angles is important.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly from a 3.3V or 5V logic supply?
A: No. You must use a series current-limiting resistor. For a 3.3V supply and a target current of 20mA, the resistor value would be R = (3.3V - 2.4V) / 0.02A = 45 Ohms. A standard 47 Ohm resistor would be suitable.

Q: Why is there such a large range in luminous intensity (11.2 to 180 mcd)?
A: This is the total production spread. Through the binning system (L through R), you can purchase LEDs from a specific, narrower intensity range to ensure consistency in your application.

Q: Is the 30mA DC current rating a recommended operating point?
A: No. The typical test condition is 20mA. The 30mA rating is the absolute maximum. For reliable long-term operation, it is advisable to derate and operate below this maximum, e.g., at 20mA.

Q: How do I interpret the \"Water Clear\" lens color?
A: A water-clear (transparent) lens allows the true color of the LED chip to be seen when off and provides the widest possible viewing angle for the emitted light when on. It is different from a diffused or colored lens.

11. Practical Design and Usage Case

Case: Designing a status indicator for a slim Bluetooth earphone case. The internal height of the case is extremely limited. A standard LED would be too tall. The LTST-C194KRKT, with its 0.3mm height, can be mounted on the internal PCB. A Bin M or N LED (18-45 mcd) would provide adequate brightness for a charging/full indicator visible through a small window. The designer would implement a drive circuit with a series resistor connected to the microcontroller's GPIO pin. The PCB land pattern would follow the datasheet recommendation, and the assembly house would use the provided IR reflow profile guidelines. The LEDs would be ordered on 7\" reels for automated assembly, and the factory would adhere to the 672-hour floor life after bag opening to ensure soldering quality.

12. Technology Principle Introduction

The LTST-C194KRKT is based on AlInGaP semiconductor technology. When a forward voltage is applied across the PN 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 Aluminum, Indium, Gallium, and Phosphide layers in the semiconductor crystal determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, red at ~631-639 nm. The water-clear epoxy lens serves to protect the semiconductor die, shape the light output beam (130-degree viewing angle), and provide mechanical stability for the wire bonds connecting the die to the package leads.

13. Industry Trends and Developments

The trend in indicator and small-signal LEDs continues toward miniaturization and higher efficiency. The 0.3mm height of this device represents an ongoing effort to reduce component profile for ever-thinner end products. Furthermore, there is a continuous push for higher luminous efficacy (more light output per unit of electrical input) across all colors, driven by energy efficiency demands. The standardization of packaging (like the EIA standard and tape-and-reel specs used here) and process compatibility (IR reflow) are also key trends, allowing LEDs to be treated as standard SMD components in high-speed assembly lines. The move to lead-free and RoHS-compliant materials, as seen in this product, is now a universal industry requirement.