LTST-C191KRKT SMD LED Datasheet - Size 1.6x0.8x0.55mm - Voltage 2.4V - Power 75mW - Red Color - English Technical Document

1. Product Overview

The LTST-C191KRKT 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, offering a significant advantage in applications where vertical profile is a critical design factor.

Core Advantages: The primary advantage of this component is its exceptionally low profile of 0.55mm, making it suitable for ultra-slim consumer electronics, wearable devices, and indicator applications behind thin panels. It utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material, which is known for producing high-efficiency red light with good brightness and color purity. The device is fully compliant with RoHS (Restriction of Hazardous Substances) directives, qualifying it as a green product for global markets.

Target Market: This LED is targeted at applications requiring reliable, bright indicators in a minimal footprint. Typical use cases include status indicators in smartphones, tablets, laptops, automotive dashboard clusters, industrial control panels, and consumer appliances. Its compatibility with automatic placement equipment and infrared reflow soldering processes makes it ideal for high-volume, automated manufacturing lines.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical, optical, and thermal parameters specified in the datasheet.

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 at an ambient temperature (Ta) of 25°C. Exceeding this limit risks overheating the semiconductor junction, leading to accelerated degradation or catastrophic failure.
• DC Forward Current (IF): 30 mA. The maximum continuous forward current that can be applied. For reliable long-term operation, it is standard practice to drive the LED below this maximum, often at the typical test condition of 20mA.
• Peak Forward Current: 80 mA (at 1/10 duty cycle, 0.1ms pulse width). This rating allows for short, high-current pulses, which can be useful for multiplexing schemes or achieving momentary high brightness, but the average current must still respect the DC rating.
• Reverse Voltage (VR): 5 V. Applying a reverse bias voltage exceeding this value can cause immediate breakdown and destruction of the LED's PN junction.
• Operating & Storage Temperature Range: -55°C to +85°C. This wide range ensures the component's functionality and storage integrity across harsh environmental conditions, from industrial freezers to hot automotive interiors.

2.2 Electro-Optical Characteristics

These parameters, measured at Ta=25°C and IF=20mA (unless noted), define the device's performance under normal operating conditions.

• Luminous Intensity (Iv): 54.0 mcd (Typical), with a range from 18.0 mcd (Min) to 180.0 mcd (Max). This wide range is managed through a binning system (see Section 3). Luminous intensity is measured using a sensor filtered to match the human eye's photopic response (CIE curve).
• Viewing Angle (2θ1/2): 130 degrees (Typical). This is the full angle at which the luminous intensity drops to half of its value measured on-axis (0°). A 130° angle indicates a very wide viewing pattern, suitable for indicators that need to be seen from off-axis positions.
• Peak Wavelength (λP): 639 nm (Typical). This is the wavelength at which the spectral power output is maximum. It defines the perceived hue of the red light.
• Dominant Wavelength (λd): 631 nm (Typical at IF=20mA). This is a colorimetric quantity derived from the CIE chromaticity diagram. It represents the single wavelength of a monochromatic light that would match the color of the LED. It is often a more relevant parameter for color specification than peak wavelength.
• Spectral Line Half-Width (Δλ): 20 nm (Typical). This is the spectral bandwidth measured at half the maximum intensity (Full Width at Half Maximum - FWHM). A value of 20nm indicates a relatively narrow spectral emission, characteristic of AlInGaP technology, resulting in a saturated red color.
• Forward Voltage (VF): 2.4 V (Typical), with a maximum of 2.4V and a minimum of 2.0V at 20mA. This is the voltage drop across the LED when operating. It is crucial for designing the current-limiting circuitry. The datasheet notes a derating of forward current above 50°C at 0.4 mA/°C, meaning the maximum allowable DC current decreases as temperature rises to prevent overheating.
• Reverse Current (IR): 10 μA (Max) at VR=5V. This is the small leakage current that flows when the device is reverse-biased within its maximum rating.
• Capacitance (C): 40 pF (Typical) at VF=0V, f=1MHz. This parasitic capacitance can be relevant in high-speed switching or multiplexing applications.

3. Binning System Explanation

To manage natural variations in the semiconductor manufacturing process, LEDs are sorted into performance bins. The LTST-C191KRKT uses a binning system primarily for luminous intensity.

Luminous Intensity Binning: The LEDs are categorized into five bins (M, N, P, Q, R) based on their measured luminous intensity at 20mA. Each bin has a defined minimum and maximum value (e.g., Bin M: 18.0-28.0 mcd, Bin R: 112.0-180.0 mcd). The datasheet specifies a tolerance of +/-15% on each intensity bin. This system allows designers to select LEDs with consistent brightness for their application. For example, a product requiring uniform panel illumination would specify LEDs from a single, tight bin (e.g., Bin P or Q), while a cost-sensitive application with less critical brightness matching might use a broader mix.

The datasheet does not indicate separate binning for dominant wavelength or forward voltage in the provided content, suggesting these parameters are controlled to fall within the published min/typ/max ranges without further sorting codes for this specific part number.

4. Performance Curve Analysis

While the specific graphs are not rendered in the text, the datasheet references typical characteristic curves. Based on standard LED behavior and the given parameters, we can analyze the expected trends:

• I-V (Current-Voltage) Curve: The forward voltage (VF) has a typical value of 2.4V at 20mA. The curve would show an exponential relationship, with very little current flowing below the "turn-on" voltage (~1.8-2.0V for AlInGaP), after which current increases rapidly with a small increase in voltage. This underscores why LEDs must be driven with a current source or a voltage source with a series current-limiting resistor.
• Luminous Intensity vs. Forward Current (Iv-IF): Luminous intensity is approximately proportional to forward current in the normal operating range. Driving the LED at a current lower than 20mA will reduce brightness proportionally, while driving it higher (up to the absolute maximum) will increase brightness but also generate more heat and potentially reduce lifespan.
• Luminous Intensity vs. Ambient Temperature (Iv-Ta): The luminous output of AlInGaP LEDs typically decreases as the ambient temperature increases. This is due to reduced internal quantum efficiency at higher temperatures. The derating specification (0.4 mA/°C above 50°C) is a direct measure to counteract this thermal effect on performance and reliability.
• Spectral Distribution: The spectrum would show a single peak centered around 639 nm (λP) with a narrow 20 nm (Δλ) width, confirming the pure red color emission.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED is packaged in a standard EIA (Electronic Industries Alliance) compliant surface-mount package. The key mechanical feature is its height of 0.55 mm (H), qualifying it as "Super Thin." The other primary dimensions (length and width) are typical for a chip LED in this class, likely around 1.6mm x 0.8mm, though the exact drawing is referenced in the datasheet. All dimensional tolerances are ±0.10 mm unless otherwise specified.

5.2 Polarity Identification and Pad Design

The datasheet includes a suggestion for soldering pad dimensions. Proper pad layout is critical for reliable soldering and preventing tombstoning. The cathode (negative side) is typically marked, often by a green tint on the package body or a notch/chamfer. The recommended pad design will include thermal relief patterns to ensure even heating during reflow and a stable mechanical connection.

6. Soldering and Assembly Guidelines

Adherence to these guidelines is essential for maintaining device reliability and preventing damage during the assembly process.

• Reflow Soldering: The LED is compatible with infrared reflow processes. The specified condition is a peak temperature of 260°C for a maximum of 5 seconds. A pre-heat stage of 150-200°C for up to 120 seconds is recommended to minimize thermal shock. The device should not be subjected to more than two reflow cycles.
• Hand Soldering: If necessary, a soldering iron may be used with a maximum tip temperature of 300°C and a soldering time not exceeding 3 seconds per lead. This should be a one-time operation only.
• Cleaning: Only specified cleaning agents should be used. The datasheet recommends immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute if cleaning is required. Unspecified chemicals may damage the plastic lens or epoxy package.
• Storage: LEDs should be stored in an environment not exceeding 30°C and 60% relative humidity. Once removed from their original moisture-barrier packaging, they should be IR-reflowed within 672 hours (28 days, MSL 2a). For longer storage outside the original bag, they must be kept in a sealed container with desiccant or in a nitrogen desiccator. If stored beyond 672 hours, a bake-out at 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent "popcorning" during reflow.

7. Packaging and Ordering Information

The LTST-C191KRKT is supplied in industry-standard packaging for automated assembly.

• Tape and Reel: The devices are packaged in 8mm wide embossed carrier tape on 13-inch (330mm) diameter reels.
• Packing Quantity: Standard reels contain 5000 pieces. For quantities less than a full reel, a minimum packing quantity of 500 pieces is available for remainders.
• Packaging Standards: The packaging conforms to ANSI/EIA-481 specifications. The tape uses a top cover to seal empty component pockets. The maximum allowed number of consecutive missing components ("missing lamps") in the tape is two.

8. Application Notes and Design Considerations

8.1 Drive Circuit Design

An LED is a current-operated device. Its brightness is controlled by forward current, not voltage. To ensure uniform brightness when driving multiple LEDs, especially in parallel, it is strongly recommended to use a dedicated current-limiting resistor in series with each LED (Circuit Model A).

Circuit Model A (Recommended): [Vcc] -- [Resistor] -- [LED] -- [GND]. This configuration compensates for the natural variation in forward voltage (VF) between individual LEDs. Even with the same applied voltage, LEDs with a slightly lower VF would draw more current and appear brighter if connected in parallel without individual resistors.

Circuit Model B (Not Recommended for Parallel): Connecting multiple LEDs directly in parallel to a single current-limiting resistor is discouraged. Differences in the I-V characteristics will cause current hogging, where one LED draws most of the current, leading to non-uniform brightness and potential over-stress of one device.

8.2 Electrostatic Discharge (ESD) Protection

LEDs are sensitive to electrostatic discharge. ESD damage may not cause immediate failure but can degrade performance, leading to high reverse leakage current, low forward voltage, or failure to illuminate at low currents.

Prevention Measures:

• Use conductive wrist straps or anti-static gloves when handling LEDs.
• Ensure all workstations, equipment, and storage racks are properly grounded.
• Use an ionizer to neutralize static charge that may build up on the plastic lens during handling.

Testing for ESD Damage: Suspect LEDs can be tested by checking for illumination and measuring forward voltage (Vf) at a very low current (e.g., 0.1mA). For this AlInGaP product, a "good" LED should have a Vf > 1.4V at 0.1mA. A significantly lower Vf or no light emission indicates potential ESD damage.

8.3 Application Scope and Reliability

The datasheet specifies that this LED is intended for ordinary electronic equipment (office equipment, communications, household appliances). For applications requiring exceptional reliability where failure could jeopardize life or health (aviation, medical devices, safety systems), consultation with the manufacturer is required prior to design-in. The document references standard reliability tests (endurance tests) conducted per industry standards to ensure product robustness under typical operating conditions.

9. Technical Comparison and Differentiation

The LTST-C191KRKT's primary differentiation lies in its combination of attributes:

• vs. Standard Thickness LEDs: Its 0.55mm height is a key advantage, enabling designs impossible with traditional 1.0mm+ height LEDs.
• vs. Other Red LED Technologies: The use of AlInGaP, compared to older GaAsP or GaP technologies, provides higher luminous efficiency (more light output per mA), better color saturation (narrower spectrum), and superior performance at elevated temperatures.
• vs. Non-Reel Packaged LEDs: The 8mm tape-on-reel packaging ensures compatibility with high-speed pick-and-place machines, a critical factor for mass production efficiency compared to bulk or stick packaging.

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 example, with a 3.3V supply and a target current of 20mA (VF typ=2.4V), the resistor value would be R = (3.3V - 2.4V) / 0.020A = 45 Ohms. A standard 47 Ohm resistor would be suitable.

Q: Why is there such a wide range in luminous intensity (18-180 mcd)?
A: This reflects the natural process variation. The binning system (M through R) allows you to purchase LEDs guaranteed to be within a specific, narrower brightness range for your application's consistency needs.

Q: Is the 260°C reflow temperature a requirement or a maximum?
A: It is the maximum peak temperature the package can withstand for 5 seconds. A typical reflow profile will ramp up to a peak slightly below this (e.g., 245-250°C) to provide a safety margin.

Q: How do I ensure uniform brightness in a multi-LED array?
A: Use Circuit Model A: an individual current-limiting resistor for each LED. Also, specify LEDs from the same intensity bin from your supplier.

11. Practical Design and Usage Examples

Example 1: Smartphone Notification LED: The ultra-thin 0.55mm profile allows this LED to be placed behind the increasingly thin glass and OLED displays of modern smartphones. Its wide 130° viewing angle ensures the notification glow is visible even when the phone is lying flat on a table. The designer would select a specific intensity bin (e.g., Bin P or Q) to achieve the desired brightness level and pair it with a suitable current-limiting resistor driven by the phone's PMIC (Power Management IC).

Example 2: Automotive Climate Control Panel Backlighting: Multiple LTST-C191KRKT LEDs could be used to backlight buttons or icons. Their compatibility with IR reflow allows them to be soldered onto the same PCB as other components. The wide operating temperature range (-55°C to +85°C) ensures reliable operation in the vehicle's interior under all climatic conditions. The designer must account for the derating of forward current at high ambient temperatures near the heater vents.

12. Technical Principle Introduction

The LTST-C191KRKT 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 dictates the wavelength (color) of the emitted light—in this case, red at approximately 639 nm. The "Water Clear" lens material is typically a colorless epoxy or silicone that does not alter the inherent color of the chip, allowing the pure red light to pass through efficiently. The thin package is achieved through advanced molding and die-attach techniques that minimize the distance between the light-emitting chip and the top of the lens.

13. Industry Trends and Development

The trend in indicator and backlight LEDs continues toward higher efficiency, smaller footprints, and lower profiles. The 0.55mm height of this device represents a step in the miniaturization trend driven by consumer electronics. There is also a continuous push for higher luminous efficacy (more lumens per watt) even for small signal LEDs, reducing power consumption in battery-operated devices. Furthermore, integration is a trend, with some applications moving toward LED drivers with built-in current regulation and diagnostics. However, discrete components like the LTST-C191KRKT remain essential for design flexibility, cost-effectiveness in high-volume applications, and their proven reliability in standardized packages compatible with global assembly infrastructure.