SMD LED LTST-C191KSKT-5A Datasheet - 0.55mm Height - 2.0V Forward Voltage - Yellow Color - 75mW Power Dissipation - English Technical Document

1. Product Overview

The LTST-C191KSKT-5A is a surface-mount device (SMD) LED designed for modern, space-constrained electronic applications. Its primary positioning is as a high-brightness, ultra-compact indicator or backlighting source. The core advantage of this component lies in its exceptionally low profile of just 0.55mm, making it suitable for applications where vertical clearance is critical, such as in ultra-thin consumer electronics, wearable devices, and advanced display panels.

The target market includes manufacturers of office equipment, communication devices, and household appliances requiring reliable, bright, and miniaturized status indicators. The product is compliant with RoHS directives, ensuring it meets international environmental standards for hazardous substance restriction. It is packaged on 8mm tape wound onto 7-inch diameter reels, making it fully compatible with high-speed automated pick-and-place assembly lines, which is essential for mass production efficiency.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Optical Characteristics

The LED utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) chip, which is known for producing high-efficiency yellow light. At a standard test current (IF) of 5mA and an ambient temperature (Ta) of 25°C, the luminous intensity (Iv) ranges from a minimum of 11.2 millicandelas (mcd) to a maximum of 45.0 mcd, with a typical value provided for reference. This wide range is managed through a binning system (detailed later). The viewing angle (2θ1/2) is specified as 130 degrees, indicating a very wide emission pattern suitable for applications requiring broad-area illumination or visibility from wide angles.

The dominant wavelength (λd), which defines the perceived color, is between 587.0 nm and 594.5 nm at 5mA, placing it firmly in the yellow spectrum. The peak emission wavelength (λp) is typically 588 nm. The spectral line half-width (Δλ) is approximately 15 nm, indicating a relatively pure color emission with minimal spectral spread.

2.2 Electrical Parameters

The forward voltage (VF) at 5mA is typically 2.00V, with a permissible range from 1.70V to 2.30V. This parameter is crucial for circuit design to ensure proper current limiting. The absolute maximum DC forward current is 30 mA, but for reliable long-term operation, driving at or below the test condition of 5mA is standard. A peak forward current of 80 mA is allowed under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The reverse voltage rating is 5V, which is a standard protection level against accidental reverse bias. The device has a low reverse current (IR) of 10 μA maximum at 5V reverse bias and a typical capacitance (C) of 40 pF at 0V and 1MHz.

2.3 Thermal and Power Characteristics

The maximum power dissipation is rated at 75 mW. This parameter defines the total electrical power (VF * IF) that can be converted into light and heat without damaging the device. The datasheet specifies a derating factor of 0.4 mA/°C for the forward current, starting from 50°C. This means that for every degree Celsius above 50°C, the maximum allowable continuous forward current must be reduced by 0.4 mA to prevent overheating and ensure longevity. The operating and storage temperature range is from -55°C to +85°C, indicating robust performance across a wide environmental range.

3. Binning System Explanation

To ensure consistency in mass production, the LEDs are sorted into bins based on key parameters. This allows designers to select parts that meet specific application requirements for color and brightness uniformity.

3.1 Forward Voltage Binning

Forward voltage is binned into three codes: E2 (1.70V - 1.90V), E3 (1.90V - 2.10V), and E4 (2.10V - 2.30V). A tolerance of ±0.1V is applied to each bin. Selecting LEDs from the same voltage bin helps maintain consistent brightness when multiple LEDs are driven in parallel from a common voltage source.

3.2 Luminous Intensity Binning

Luminous intensity is categorized into three bins: L (11.2 - 18.0 mcd), M (18.0 - 28.0 mcd), and N (28.0 - 45.0 mcd). A tolerance of ±15% is applied to each bin. This binning is critical for applications where uniform perceived brightness across multiple indicators is important.

3.3 Dominant Wavelength Binning

The yellow color is controlled through dominant wavelength bins: J (587.0 - 589.5 nm), K (589.5 - 592.0 nm), and L (592.0 - 594.5 nm). The tolerance for each bin is ±1 nm. This precise control ensures minimal color variation between different production batches or within an array of LEDs.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (Fig.1, Fig.6), their typical behavior can be described based on semiconductor physics and the provided parameters.

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

The AlInGaP chip exhibits a characteristic I-V curve where the forward voltage increases logarithmically with current. The typical VF of 2.0V at 5mA is a key operating point. Driving the LED at higher currents will increase VF slightly (towards the max of 2.3V) and significantly increase light output, but it will also increase power dissipation and junction temperature, which must be managed within the absolute maximum ratings.

4.2 Temperature Characteristics

The luminous intensity of LEDs generally decreases as the junction temperature increases. The derating specification (0.4 mA/°C above 50°C) is a direct consequence of this thermal behavior. High ambient temperatures or excessive drive current leading to self-heating will reduce light output and can accelerate degradation if limits are exceeded.

4.3 Spectral Distribution

The spectral output is centered around 588 nm (peak) with a narrow half-width of 15 nm. This results in a saturated yellow color. The dominant wavelength may shift slightly with changes in drive current and temperature, but the binning system ensures the final color remains within the specified narrow bands.

5. Mechanical and Packaging Information

5.1 Physical Dimensions

The LED features an industry-standard EIA package footprint. The key dimension is its height of 0.55mm, which defines its \"ultra-thin\" characteristic. Detailed mechanical drawings in the datasheet provide length, width, and other critical dimensions for PCB land pattern design, all in millimeters with a standard tolerance of ±0.10 mm unless otherwise noted.

5.2 Soldering Pad Design

The datasheet includes suggested soldering pad dimensions. Following these recommendations is crucial for achieving a reliable solder joint during reflow processes, ensuring proper mechanical attachment and thermal/electrical connection. The pad design accounts for the component's size and the necessary solder fillet.

5.3 Polarity Identification

The component has an anode and cathode. The datasheet diagram indicates the polarity, typically marked on the device itself or identifiable by its internal structure and external features. Correct polarity orientation during assembly is mandatory for the device to function.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Parameters

The LED is compatible with both infrared (IR) and vapor phase reflow soldering processes. For a standard process, a peak temperature of 260°C for a maximum of 5 seconds is specified. For lead-free (Pb-free) processes, a specific reflow profile is suggested, typically involving a slightly higher peak temperature or adjusted ramp rates. Adhering to these profiles prevents thermal damage to the LED's epoxy package and the semiconductor die.

6.2 Precautions and Storage Conditions

LEDs should be stored in an environment not exceeding 30°C and 70% relative humidity. Once removed from their original moisture-barrier packaging, they should be reflow-soldered within 672 hours (28 days) to prevent moisture absorption, which can cause \"popcorning\" or delamination during reflow. If storage exceeds this period, a baking process (e.g., 60°C for 24 hours) is recommended to remove moisture.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is acceptable. Unspecified chemicals may damage the plastic lens or the package integrity.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The product is supplied in embossed carrier tape with a width of 8mm, wound on standard 7-inch (178mm) diameter reels. Each reel contains 5000 pieces. The packaging conforms to ANSI/EIA 481-1-A-1994 specifications. A top cover tape seals the component pockets. There are guidelines for the maximum number of consecutive missing components and minimum packing quantities for remainder parts.

7.2 Part Number Structure

The part number LTST-C191KSKT-5A encodes specific product attributes. While the full corporate naming logic may be proprietary, it typically includes series identifiers (LTST), size/code (C191), color/lens type (KSKT for water clear lens with a yellow AlInGaP chip), and possibly bin or variant information (5A).

8. Application Recommendations

8.1 Typical Application Scenarios

This LED is ideal for status indicators, backlighting for buttons or symbols, and panel illumination in devices where height is a constraint. Examples include smartphones, tablets, ultra-thin laptops, remote controls, automotive dashboard indicators (where space behind the panel is limited), and portable medical devices.

8.2 Circuit Design Considerations

LEDs are current-driven devices. To ensure uniform brightness, especially when multiple LEDs are connected in parallel, it is strongly recommended to use a series current-limiting resistor for each LED. Driving multiple LEDs in parallel directly from a voltage source (without individual resistors) is discouraged because small variations in the forward voltage (VF) characteristic between individual LEDs can cause significant differences in current sharing and, consequently, brightness. A simple drive circuit consists of a voltage source, a series resistor (R = (Vsource - VF) / IF), and the LED.

8.3 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge. Handling precautions must be observed: use grounded wrist straps and work surfaces, store components in anti-static packaging, and employ ionizers to neutralize static charges that may accumulate on the plastic lens. ESD events can cause immediate failure or latent damage that shortens the device's lifespan.

9. Technical Comparison and Differentiation

The primary differentiating factor of the LTST-C191KSKT-5A is its 0.55mm height. Compared to standard chip LEDs which are often 0.6mm or 0.8mm tall, this represents a significant reduction for the thinnest designs. The use of AlInGaP technology provides higher efficiency and brighter yellow light compared to older technologies like GaAsP on GaP for the same color. Its compatibility with standard IR reflow processes and tape-and-reel packaging makes it as easy to assemble as any other SMD component, despite its advanced thin profile.

10. Frequently Asked Questions Based on Technical Parameters

Q: Can I drive this LED at 20mA continuously?

A: The absolute maximum DC forward current is 30 mA, so 20mA is within the limit. However, you must check the power dissipation (P = VF * IF). At 20mA and a typical VF of 2.0V, power is 40mW, which is below the 75mW maximum. Ensure the ambient temperature is considered, and apply current derating if the operating temperature exceeds 50°C.

Q: Why is there such a wide range in luminous intensity (11.2 to 45.0 mcd)?

A: This range represents the total spread across all production. Through the binning system (L, M, N), manufacturers can purchase LEDs from a specific, narrower intensity bin to ensure consistency in their application.

Q: What is the difference between peak wavelength and dominant wavelength?

A: Peak wavelength (λp) is the wavelength at which the spectral power output is maximum. Dominant wavelength (λd) is derived from the color coordinates on the CIE diagram and represents the single wavelength of a pure monochromatic light that would match the perceived color of the LED. For a narrow-spectrum LED like this, they are often very close.

Q: Is a heat sink required?

A: For typical operation at 5mA or similar low currents, no dedicated heat sink is needed as the power dissipation is very low. The PCB itself acts as a heat sink. For operation near the maximum current ratings, careful thermal management of the PCB layout is advised.

11. Practical Design and Usage Case

Consider designing a status indicator for a new smartwatch. The main board has extremely limited Z-height. The LTST-C191KSKT-5A, with its 0.55mm height, can fit beneath a thin diffuser layer. The designer selects parts from the \"M\" intensity bin and \"K\" wavelength bin to ensure all watch units have a consistent, pleasant yellow glow for notification alerts. A 3.3V supply rail is used. The series resistor is calculated as R = (3.3V - 2.0V) / 0.005A = 260 Ohms. A standard 270-ohm resistor is chosen, resulting in a current of approximately 4.8mA, safely within limits. The wide 130-degree viewing angle ensures the indicator is visible from various angles when glancing at the wrist.

12. Operating Principle Introduction

An LED is a semiconductor p-n junction diode. 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 junction region. When these charge carriers recombine, energy is released in the form of photons (light). The color of the light is determined by the bandgap energy of the semiconductor material. The AlInGaP (Aluminum Indium Gallium Phosphide) material system used in this LED has a bandgap corresponding to yellow light. The \"water clear\" lens is typically made of epoxy and is designed to efficiently extract the light generated inside the semiconductor chip.

13. Technology Development Trends

The trend in indicator LEDs continues towards higher efficiency (more light output per electrical watt), smaller form factors, and lower profiles. The 0.55mm height of this device represents the ongoing push for miniaturization. Future developments may involve even thinner packages, integration of driver ICs within the LED package (smart LEDs), and expanded color gamuts or improved color rendering for lighting applications. Furthermore, advancements in substrate materials and chip design aim to reduce efficiency droop (the decrease in efficiency at higher currents) and improve reliability at higher operating temperatures. The drive for broader adoption of lead-free and halogen-free materials in compliance with evolving environmental regulations also remains a key industry focus.