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

1. Product Overview

LTST-C191KRKT is a surface-mount device (SMD) light-emitting diode (LED) designed specifically for modern space-constrained electronic applications. It belongs to the ultra-thin chip LED category, offering significant advantages in applications where vertical height is a critical design factor.

Core Advantages:The primary advantage of this component is its extremely low profile of 0.55mm, making it suitable for ultra-thin consumer electronics, wearable devices, and indicator light applications behind thin panels. It utilizes AlInGaP (aluminum indium gallium phosphide) semiconductor material, renowned for producing red light with high efficiency, high brightness, and high color purity. The device is fully compliant with the RoHS (Restriction of Hazardous Substances) directive, making it a green product suitable for the global market.

Target Market:This LED primarily targets applications requiring reliable, bright indicators within extremely confined spaces. Typical use cases include status indicator lights in smartphones, tablets, laptops, automotive dashboards, industrial control panels, and consumer appliances. Its compatibility with automatic placement equipment and infrared reflow soldering processes makes it an ideal choice for high-volume automated production lines.

2. In-depth Technical Parameter Analysis

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

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device and are not applicable under normal operating conditions.

• Power Dissipation (Pd):75 mW. This is the maximum heat that the LED package can dissipate when the ambient temperature (Ta) is 25°C. Exceeding this limit risks overheating, which may lead to accelerated aging of the semiconductor junction or catastrophic failure.
• DC Forward Current (IF):30 mA. The maximum continuous forward current that can be applied. To ensure long-term reliable operation, standard practice is to drive the LED below this maximum, typically operating under a typical test condition of 20mA.
• Peak Forward Current:80 mA (duty cycle 1/10, pulse width 0.1ms). This rating allows for short-duration, high-current pulses, which can be used in multiplexing schemes or to achieve instantaneous high brightness, but the average current must still comply with the DC rating.
• Reverse Voltage (VR):5 V. Applying a reverse bias voltage exceeding this value may cause immediate breakdown and damage to the LED's PN junction.
• Operating and Storage Temperature Range:-55°C to +85°C. This wide range ensures the functionality and storage integrity of the component in various harsh environmental conditions, from industrial freezing environments to high-temperature automotive interiors.

2.2 Electro-Optical Characteristics

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

• Luminous Intensity (Iv):54.0 mcd (Typical), ranging 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 photopic response of the human eye (CIE curve).
• Viewing Angle (2θ1/2):130 degrees (typical). This is the full angle at which the luminous intensity drops to half of the axial (0°) measured value. A viewing angle of 130° indicates a very wide emission pattern, suitable for indicator lights that need to be viewed from off-axis positions.
• Peak Wavelength (λP):639 nm (typical value). This is the wavelength at which the spectral power output reaches its maximum, determining the perceived hue of the red light.
• Dominant Wavelength (λd):631 nm (typical value at IF=20mA). This is a colorimetric quantity derived from the CIE chromaticity diagram. It represents the wavelength of monochromatic light that matches the color of the LED. For color specification, it is often a more relevant parameter than the peak wavelength.
• Spectral Line Half-Width (Δλ):20 nm (typical). This is the spectral bandwidth measured at half of the maximum intensity (Full Width at Half Maximum - FWHM). The 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 during operation, crucial for designing current-limiting circuits. The datasheet specifies that above 50°C, the forward current must be derated by 0.4 mA/°C, meaning the maximum allowable DC current decreases with increasing temperature 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 ratings.
• Capacitance (C):40 pF (typical), under conditions VF=0V, f=1MHz. This parasitic capacitance may be relevant in high-speed switching or multiplexing applications.

3. Grading System Description

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

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

In the provided content, the datasheet does not indicate separate binning for dominant wavelength or forward voltage, suggesting these parameters are controlled within the published min/typ/max ranges without the need for further binning codes for this specific model.

4. Performance Curve Analysis

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

• I-V (Current-Voltage) Curve:The typical forward voltage (VF) at 20mA is 2.4V. This curve exhibits an exponential relationship, with almost no current flowing below the "turn-on" voltage (approximately 1.8-2.0V for AlInGaP), after which the current increases rapidly with a small increase in voltage. This emphasizes why an LED must be driven by a current source or a voltage source with a series current-limiting resistor.
• Luminous Intensity vs. Forward Current (Iv-IF):Within the normal operating range, luminous intensity is approximately proportional to the forward current. Driving an LED with a current below 20mA will proportionally reduce its brightness, while driving it with a higher current (up to the absolute maximum) will increase brightness but also generate more heat and may shorten its lifespan.
• Luminous Intensity vs. Ambient Temperature (Iv-Ta):The light output of AlInGaP LEDs typically decreases with increasing ambient temperature. This is due to a reduction in 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 will show a single peak centered at 639 nm (λP) with a width of 20 nm (Δλ), confirming pure red light emission.

5. Mechanical and Packaging Information

5.1 Package Dimensions

This LED is packaged in a surface-mount device (SMD) compliant with the EIA (Electronic Industries Alliance) standard. Its key mechanical feature is a height of 0.55 mm (H), qualifying it as "ultra-thin." Other primary dimensions (length and width) are typical for this type of chip LED, likely around 1.6mm x 0.8mm, but please refer to the specification sheet for detailed drawings. Unless otherwise specified, all dimensional tolerances are ±0.10 mm.

5.2 Polarity Identification and Pad Design

The specification sheet includes recommendations for solder pad dimensions. Correct pad layout is crucial for reliable soldering and preventing tombstoning. The cathode (negative side) is typically marked, for example, by a green tint or a notch/chamfer on the package body. The recommended pad design will incorporate a thermal pad pattern to ensure uniform heating during reflow soldering and a stable mechanical connection.

6. Soldering and Assembly Guide

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

• Reflow soldering:This LED is compatible with infrared reflow processes. The specified conditions are a peak temperature of 260°C for a maximum of 5 seconds. A preheating 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 the tip temperature not exceeding 300°C and the soldering time per pin not exceeding 3 seconds. This operation should be performed only once.
• Cleaning:Only the specified cleaning agents should be used. The datasheet recommends that if cleaning is required, immersion in ethanol or isopropanol at room temperature for no more than one minute is acceptable. Unspecified chemicals may damage the plastic lens or epoxy package.
• Storage:LED should be stored in an environment not exceeding 30°C and 60% relative humidity. Once removed from the original moisture barrier bag, infrared reflow soldering must be performed within 672 hours (28 days, MSL 2a). For long-term storage outside the original bag, they must be kept in a sealed container with desiccant or a nitrogen dry box. If storage exceeds 672 hours, baking at 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent the "popcorn" effect during reflow.

7. Packaging and Ordering Information

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

• Tape and Reel:The device is packaged on an 8mm wide embossed carrier tape with a reel diameter of 13 inches (330mm).
• Package Quantity:The standard reel contains 5000 pieces. For quantities less than a full reel, the minimum packaging quantity for the remainder is 500 pieces.
• Packaging Standard:Packaging complies with ANSI/EIA-481 specification. The carrier tape uses a top cover to seal empty component pockets. The maximum number of consecutive missing components ("missing LEDs") allowed in the carrier tape is two.

8. Application Notes and Design Considerations

8.1 Drive Circuit Design

LED is a current-driven device. Its brightness is controlled by the forward current, not voltage. To ensure uniform brightness when driving multiple LEDs (especially in parallel),Strongly recommendedConnect a dedicated current-limiting resistor in series for each LED (Circuit Model A).

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

Circuit Model B (not recommended for parallel connection):It is not recommended to connect multiple LEDs directly in parallel to a single current-limiting resistor. Differences in I-V characteristics will lead to uneven current distribution, where one LED will draw most of the current, resulting in uneven brightness and subjecting one device to potential overstress.

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.

Preventive Measures:

• Use conductive wrist straps or anti-static gloves when handling LEDs.
• Ensure all workstations, equipment, and storage racks are properly grounded.
• Use ionizers to neutralize static charges that may accumulate on plastic lenses during processing.

8.3 Application Scope and Reliability

The datasheet specifies that this LED is suitable for general electronic equipment (office equipment, communication, household appliances). For applications requiring extremely high reliability where failure could endanger life or health (aviation, medical equipment, security systems), consultation with the manufacturer is required before design adoption. The document references standard reliability tests (endurance tests) conducted according to industry standards to ensure product robustness under typical operating conditions.

9. Technical Comparison and Differentiation

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

• Compared to standard thickness LEDs:Its 0.55mm height is a key advantage, enabling designs not possible with traditional 1.0mm+ height LEDs.
• Compared with other red LED technologies:Compared to older GaAsP or GaP technologies, AlInGaP offers higher luminous efficiency (more light output per mA), better color saturation (narrower spectrum), and superior performance at high temperatures.
• Compared with non-reel packaged LEDs:8mm tape and reel packaging ensures compatibility with high-speed pick-and-place machines, which is a key factor for achieving mass production efficiency compared to bulk or stick packaging.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly with a 3.3V or 5V logic power supply?
A: No. A series current-limiting resistor must be used. For example, with a 3.3V power supply and a target current of 20mA (typical VF=2.4V), the resistor value should be R = (3.3V - 2.4V) / 0.020A = 45 ohms. A standard 47-ohm resistor is suitable.

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

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

Q: How to ensure brightness uniformity in a multi-LED array?
A: Use Circuit Model A: Equip each LED with an independent current-limiting resistor. Also, specify to the supplier that the LEDs should be from the same intensity bin.

11. Practical Design and Usage Examples

Example 1: Smartphone Notification LED:The ultra-thin 0.55mm height allows this LED to be placed behind the increasingly thin glass and OLED displays of modern smartphones. Its 130° wide viewing angle ensures the notification light is visible even when the phone is lying flat on a table. Designers select specific intensity grades (e.g., grade 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 Air Conditioning Control Panel Backlight:Multiple LTST-C191KRKT LEDs can be used for button or icon backlighting. Their compatibility with infrared reflow allows them to be soldered onto the same PCB alongside other components. The wide operating temperature range (-55°C to +85°C) ensures reliable operation in all climatic conditions inside the vehicle. Designers must consider derating the forward current in high ambient temperatures near heater vents.

12. Introduction to Technical Principles

LTST-C191KRKT yana kan AlInGaP semiconductor fasaha. Lokacin da aka yi amfani da ƙarfin lantarki mai kyau a kan mahaɗin PN, ana shigar da electrons da ramuka cikin yanki mai aiki. Haɗin su yana sakin makamashi a cikin nau'in photon (haske). Takamaiman abun da ke ciki na aluminum, indium, gallium, da phosphorus layers a cikin semiconductor crystal yana ƙayyade ƙarfin tazarar band, wanda kai tsaye ke ƙayyade tsawon zangon haske da aka fitar (launi) - a cikin wannan misali, jan haske mai kusan 639 nm. Kayan ruwan tabarau "Ruwa mai tsabta" yawanci epoxy mara launi ne ko silicone, ba sa canza ainihin launin guntu, yana ba da damar jan haske mai tsabta ya wuce yadda ya kamata. Siririn kunshe yana samuwa ta hanyar ci-gaban fasahar ƙirƙira da kuma fasahar saka guntu, waɗanda ke rage matuƙar tazarar da ke tsakanin guntu mai haskakawa da saman ruwan tabarau.

13. Industry Trends and Development

Trends for indicator and backlight LEDs continue towards higher efficiency, smaller size, and lower height. The 0.55mm height of this device represents a step in the miniaturization trend driven by consumer electronics. Even for small signal LEDs, there is a continuous push for higher luminous efficacy (more lumens per watt) to reduce power consumption in battery-powered devices. Additionally, integration is also a trend, with some applications moving towards LED drivers with built-in current regulation and diagnostic functions. However, discrete components like the LTST-C191KRKT remain crucial for design flexibility, cost-effectiveness in high-volume applications, and their proven reliability in standardized packages compatible with global assembly infrastructure.