LTST-C171KGKT SMD LED Datasheet - 0.8mm Height - 2.4V Forward Voltage - Green Color - 75mW Power - English Technical Document

1. Product Overview

The LTST-C171KGKT is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, space-constrained electronic applications. It belongs to a family of ultra-thin chip LEDs, featuring a remarkably low profile of just 0.80 mm in height. This makes it an ideal choice for backlighting indicators, status lights, and decorative illumination in slim consumer electronics, automotive dashboards, and portable devices where component height is a critical design factor.

The LED utilizes an Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor chip, a technology known for producing high-efficiency light in the amber to green spectrum. This specific model emits a green light. Its construction and materials comply with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product suitable for global markets with stringent environmental regulations.

Packaged on 8mm tape and supplied on 7-inch diameter reels, the component is fully compatible with high-speed automated pick-and-place assembly equipment. It is also designed to withstand standard infrared (IR) and vapor phase reflow soldering processes, facilitating efficient and reliable mass production.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended for extended periods.

• Power Dissipation (Pd): 75 mW. This is the maximum total power the LED package can dissipate as heat at an ambient temperature (Ta) of 25°C.
• DC Forward Current (IF): 30 mA. The maximum continuous forward current that can be applied.
• Peak Forward Current: 80 mA. This is permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to prevent overheating.
• Derating: The maximum DC forward current must be linearly reduced by 0.4 mA for every degree Celsius above 50°C ambient temperature. This is crucial for thermal management in high-temperature environments.
• Reverse Voltage (VR): 5 V. Exceeding this voltage in reverse bias can cause immediate junction breakdown.
• Operating & Storage Temperature Range: -55°C to +85°C. The device is rated for operation and storage across this wide industrial temperature range.
• Infrared Soldering Condition: Withstands 260°C peak temperature for 10 seconds, which is standard for lead-free (Pb-free) solder reflow profiles.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at Ta=25°C and an IF of 20 mA, which is the standard test condition.

• Luminous Intensity (Iv): 18.0 (Min) / 35.0 (Typ) mcd. This is the perceived brightness of the light output as measured by a sensor filtered to match the human eye's photopic response (CIE curve).
• Viewing Angle (2θ1/2): 130° (Typ). This wide viewing angle indicates the LED emits light over a broad cone, making it suitable for applications requiring wide-area illumination.
• Peak Emission Wavelength (λP): 574 nm (Typ). This is the wavelength at which the spectral power output is highest.
• Dominant Wavelength (λd): 571 nm (Typ). This is the single wavelength that best represents the perceived color (green) of the LED, derived from CIE chromaticity calculations.
• Spectral Line Half-Width (Δλ): 15 nm (Typ). This measures the spectral purity; a narrower width indicates a more saturated, pure color.
• Forward Voltage (VF): 2.0 (Min) / 2.4 (Typ) V. The voltage drop across the LED when conducting 20 mA.
• Reverse Current (IR): 10 μA (Max) at VR=5V. A low reverse leakage current is desirable.
• Capacitance (C): 40 pF (Typ) at 0V, 1 MHz. This parasitic capacitance can be relevant in high-frequency switching applications.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins based on key parameters. The LTST-C171KGKT uses a three-dimensional binning system.

3.1 Forward Voltage Binning

Bins are defined by a numeric code (4 through 8) representing a range of VF @ 20mA. For example, Bin Code '5' covers LEDs with a VF between 2.00V and 2.10V. A tolerance of ±0.1V is applied to each bin. Matching VF bins in a circuit helps achieve uniform current sharing when LEDs are connected in parallel.

3.2 Luminous Intensity Binning

Bins are defined by an alphabetic code (M, N, P) representing a range of Iv @ 20mA. For instance, Bin 'M' covers 18.0 to 28.0 mcd, while Bin 'N' covers 28.0 to 45.0 mcd. A tolerance of ±15% is applied to each bin. This allows designers to select a brightness grade suitable for their application.

3.3 Dominant Wavelength Binning

Bins are defined by an alphabetic code (C, D, E) representing a range of λd @ 20mA. Bin 'D', for example, covers 570.5 nm to 573.5 nm. A tight tolerance of ±1 nm is maintained for each bin, ensuring very consistent color appearance across a batch of LEDs.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (Fig.1, Fig.6), their implications are standard. The Relative Luminous Intensity vs. Forward Current curve would show a near-linear relationship at lower currents, tending to saturate at higher currents due to thermal and efficiency effects. The Angular Intensity Distribution pattern (Fig.6) would illustrate the 130° viewing angle, showing how light intensity decreases from the center axis. The Spectral Distribution graph (Fig.1) would display a Gaussian-like curve centered around 574 nm with a 15 nm half-width, confirming the green color emission.

5. Mechanical & Packaging Information

5.1 Package Dimensions

The LED features an industry-standard EIA package outline. Key dimensions include a total height of 0.80 mm. Detailed mechanical drawings specify the length, width, lead spacing, and lens geometry, all with a standard tolerance of ±0.10 mm unless otherwise noted. These precise dimensions are critical for PCB footprint design.

5.2 Polarity Identification & Solder Pad Design

The component has an anode and cathode. The datasheet includes a suggested solder pad land pattern. This pattern is optimized for reliable solder joint formation during reflow, ensuring proper wetting and mechanical strength while preventing solder bridging. Adhering to this recommended footprint is essential for manufacturing yield.

5.3 Tape and Reel Packaging

The LEDs are supplied in embossed carrier tape (8mm pitch) wound onto 7-inch (178 mm) diameter reels. Each reel contains 3000 pieces. The packaging conforms to ANSI/EIA 481-1-A-1994 standards. Key notes include: empty pockets are sealed with cover tape, a minimum order quantity for remnants is 500 pieces, and a maximum of two consecutive missing components are allowed per reel.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

A suggested infrared reflow profile for lead-free processes is provided. Key parameters include a pre-heat zone of 150-200°C, a pre-heat time up to 120 seconds, a peak temperature not exceeding 260°C, and a time above liquidus (typically ~217°C) of 10 seconds maximum. The LED can withstand this profile a maximum of two times.

6.2 Hand Soldering

If manual soldering is necessary, a soldering iron with a temperature not exceeding 300°C should be used, with the soldering time limited to 3 seconds per joint. This should be performed only once to avoid thermal damage to the plastic package.

6.3 Cleaning

Only specified cleaning agents should be used. Recommended solvents are ethyl alcohol or isopropyl alcohol at normal room temperature. The LED should be immersed for less than one minute. Unspecified chemicals may damage the epoxy lens or package.

6.4 Storage & Moisture Sensitivity

LEDs should be stored in an environment not exceeding 30°C and 70% relative humidity. Once removed from their original moisture-barrier bag, components should be subjected to IR reflow 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 atmosphere. Components stored beyond 672 hours require baking at approximately 60°C for at least 24 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

7. Application Notes & Design Considerations

7.1 Drive Circuit Design

LEDs are current-driven devices. To ensure uniform brightness when driving multiple LEDs, especially in parallel, it is strongly recommended to use a individual current-limiting resistor in series with each LED. The datasheet illustrates this as \"Circuit Model A.\" Attempting to drive multiple LEDs in parallel from a single resistor (\"Circuit Model B\") is discouraged because small variations in the forward voltage (VF) characteristic of each LED will cause significant imbalances in current distribution, leading to uneven brightness and potential over-stressing of some devices.

7.2 Electrostatic Discharge (ESD) Protection

The AlInGaP semiconductor structure is sensitive to electrostatic discharge. ESD damage can manifest as high reverse leakage current, abnormally low forward voltage, or failure to illuminate at low currents. To prevent ESD damage:

• Operators should wear conductive wrist straps or anti-static gloves.
• All workstations, equipment, and storage racks must be properly grounded.
• Use an ionizer to neutralize static charges that may accumulate on the plastic lens during handling.

To test for potential ESD damage, check if the LED illuminates and measure its VF at a very low current (e.g., 0.1mA). A healthy AlInGaP LED should have a VF greater than 1.4V under this condition.

7.3 Application Scope

This LED is designed for general-purpose electronic equipment, including office automation devices, communication equipment, and household appliances. For applications requiring exceptional reliability where failure could risk life or health (e.g., aviation, medical systems, safety devices), specific qualification and consultation with the manufacturer are necessary prior to design-in.

8. Technical Comparison & Differentiation

The primary differentiating features of the LTST-C171KGKT are its ultra-low 0.8mm profile and the use of AlInGaP technology for green light. Compared to older technologies or thicker packages, it enables slimmer product designs. AlInGaP offers high efficiency and good temperature stability for green/amber colors. Its wide 130° viewing angle provides broad, even illumination compared to narrower-angle LEDs, which are more suited for focused beam applications. The comprehensive binning system allows for tighter color and brightness matching in production runs compared to unbinned or loosely binned components.

9. Frequently Asked Questions (FAQ)

Q: Can I drive this LED directly from a 3.3V or 5V logic output?
A: No. You must always use a series current-limiting resistor. The resistor value is calculated as R = (Vcc - VF) / IF. For example, with a 5V supply (Vcc), a VF of 2.4V, and a desired IF of 20mA, R = (5 - 2.4) / 0.02 = 130 Ohms. A standard 130 or 150 Ohm resistor would be suitable.

Q: What is the difference between Peak Wavelength and Dominant Wavelength?
A: Peak Wavelength (λP) is the physical wavelength where the LED emits the most optical power. Dominant Wavelength (λd) is a calculated value that corresponds to the perceived color by the human eye on the CIE chart. λd is often more relevant for color-indication applications.

Q: How do I interpret the bin code in the part number (e.g., KGKT)?
A: The part number suffix typically encodes the bin selections for intensity, wavelength, and sometimes voltage. The specific bin mapping (e.g., 'K' for intensity, 'G' for wavelength) is defined in the manufacturer's internal coding system and should be cross-referenced with the bin code list in the datasheet for the exact performance range.

Q: Is baking always required before soldering?
A: Baking is only required if the components have been exposed to ambient air outside their original sealed, moisture-protective bag for longer than the specified \"floor life\" (672 hours for MSL 2a). If used within this period from a properly sealed bag, baking is not necessary.

10. Design-in Case Study Example

Scenario: Designing a status indicator panel for a portable medical device. The panel has space for 10 green LEDs in a row, indicating different operational modes. The device housing has a total internal height constraint of 2.5mm.

Component Selection Rationale: The LTST-C171KGKT is chosen primarily for its 0.8mm height, which easily fits within the mechanical constraint with room for the PCB and diffuser. Its wide 130° viewing angle ensures the indicators are visible from various angles when the device is held or placed on a table. The green color (571 nm dominant wavelength) is a standard for \"ready\" or \"on\" status.

Circuit Design: A microcontroller unit (MCU) with 10 GPIO pins drives the LEDs. Each GPIO pin is connected to the anode of one LED through a 150-ohm series resistor. The cathodes are all tied to ground. This \"individual resistor per LED\" configuration (Circuit A) is used despite using more resistors because it guarantees identical current and therefore identical brightness for each LED, regardless of minor VF variations. The MCU pins are configured as open-drain or push-pull outputs to source the required ~20mA.

PCB Layout: The recommended solder pad dimensions from the datasheet are used in the PCB footprint. Adequate clearance is maintained between pads to prevent solder bridging. The LEDs are placed on the top side of the PCB, and a light guide or diffuser film is placed above them to blend the light evenly across the indicator window on the housing.

11. Technology Principle Introduction

The LTST-C171KGKT is based on Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor technology. This material system is formed by alloying Aluminum Gallium Indium Phosphide, allowing engineers to tune the bandgap energy by adjusting the ratios of these elements. A larger bandgap corresponds to shorter wavelength (higher energy) light emission. For green light (~571 nm), a specific composition is used.

When a forward voltage exceeding the diode's turn-on voltage (around 2V for AlInGaP green) is applied, electrons are injected from the n-type region into the p-type region, and holes are injected in the opposite direction. These charge carriers recombine in the active region of the semiconductor. In a direct bandgap material like AlInGaP, this recombination releases energy in the form of photons (light) through a process called electroluminescence. The wavelength (color) of the emitted photon is determined by the bandgap energy of the semiconductor material in the active region. The epoxy lens serves to protect the chip, shape the light output beam, and enhance light extraction efficiency.

12. Industry Trends & Developments

The trend in SMD LEDs for indicator and backlight applications continues toward miniaturization and higher efficiency. Package heights are shrinking below 0.8mm to enable ever-thinner end products. There is also a drive for higher luminous efficacy (more light output per electrical watt input), which reduces power consumption and heat generation. This is achieved through improvements in chip design (e.g., flip-chip structures), better internal reflectors, and advanced phosphor technologies for white LEDs. While AlInGaP is mature and efficient for red-amber-green, Indium Gallium Nitride (InGaN) technology dominates the blue, green, and white LED markets and is seeing continuous improvements in green efficiency, potentially challenging AlInGaP in some green applications. Furthermore, integration is a trend, with multi-LED packages and LED drivers combined into single modules to simplify design and save board space.