SMD LED LTST-C191KGKT-5A Datasheet - 0.55mm Height - 2.1V Max - Green - English Technical Document

1. Product Overview

This document details the specifications for the LTST-C191KGKT-5A, a surface-mount device (SMD) light-emitting diode (LED). This component is part of a family of chip LEDs designed for modern, compact electronic assemblies. The primary application is as an indicator light, status signal, or backlighting element in consumer electronics, communication devices, and general electronic equipment.

The core advantage of this product is its extremely low profile. With a height of just 0.55 millimeters, it enables the design of thinner end products. It utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for the light-emitting chip, which is known for producing high-brightness light with good efficiency in the red, orange, yellow, and green color spectrum. The device is packaged on industry-standard 8mm tape wound onto 7-inch reels, making it fully compatible with high-speed automated pick-and-place assembly equipment used in modern electronics manufacturing.

1.1 Key Features

• Ultra-Thin Profile: Package height is only 0.55 mm, facilitating sleek product designs.
• High Brightness: Utilizes an AlInGaP chip technology for superior luminous intensity.
• Automation Friendly: Supplied in 8mm tape on 7\" reels for compatibility with automated assembly lines.
• Robust Assembly: Compatible with both infrared (IR) and vapor phase reflow soldering processes, including lead-free (Pb-free) profiles.
• Standardized Package: Conforms to EIA (Electronic Industries Alliance) standard dimensions for reliable placement and soldering.
• Drive Compatibility: I.C. compatible, meaning it can be directly driven by the output of standard integrated circuits with appropriate current limiting.

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 under or at these limits is not guaranteed and should be avoided for reliable operation. All values are specified at an ambient temperature (Ta) of 25°C.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the device can dissipate as heat.
• Peak Forward Current (I_F(PEAK)): 80 mA. This is the maximum allowable instantaneous forward current, typically under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• Continuous Forward Current (I_F): 30 mA DC. The maximum current that can flow through the LED continuously.
• Current Derating: Above 25°C, the maximum allowable continuous forward current must be reduced linearly at a rate of 0.4 mA per degree Celsius increase in ambient temperature.
• Reverse Voltage (V_R): 5 V. The maximum voltage that can be applied in the reverse direction across the LED.
• Operating Temperature Range: -55°C to +85°C. The ambient temperature range over which the device is designed to function.
• Storage Temperature Range: -55°C to +85°C.
• Infrared Soldering Condition: Withstands a peak temperature of 260°C for up to 5 seconds during reflow soldering.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured under standard test conditions (Ta=25°C, I_F=5mA unless noted). They define the expected behavior of the device in normal operation.

• Luminous Intensity (I_V): Ranges from 4.5 to 18.0 millicandelas (mcd). This is a measure of the perceived brightness of the LED as seen by the human eye, measured with a filter matching the CIE photopic response curve.
• Viewing Angle (2θ_1/2): 130 degrees (typical). This is the full angle at which the luminous intensity drops to half of its value measured on-axis. A wide viewing angle like this makes the LED visible from a broad range of positions.
• Peak Emission Wavelength (λ_P): 574 nm (typical). The specific wavelength at which the emitted optical power is at its maximum.
• Dominant Wavelength (λ_d): Ranges from 564.5 to 573.5 nm at 5mA. This is the single wavelength that best represents the perceived color of the light, derived from the CIE chromaticity diagram. It defines the \"green\" color point.
• Spectral Line Half-Width (Δλ): 15 nm (typical). The width of the emission spectrum at half of its maximum power. A narrower half-width indicates a more spectrally pure color.
• Forward Voltage (V_F): Ranges from 1.70 to 2.10 Volts at 5mA. The voltage drop across the LED when it is conducting current.
• Reverse Current (I_R): 100 µA (maximum) when a reverse voltage of 5V is applied.
• Capacitance (C): 40 pF (typical) measured at 0V forward bias and 1 MHz frequency.

3. Binning System Explanation

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

3.1 Forward Voltage Binning

Units are sorted by their forward voltage (V_F) measured at 5mA. The bin code and corresponding range are:

• Bin Code 2: 1.70 V (Min) to 1.80 V (Max)
• Bin Code 3: 1.80 V to 1.90 V
• Bin Code 4: 1.90 V to 2.00 V
• Bin Code 5: 2.00 V to 2.10 V

Tolerance within each bin is ±0.1 Volt.

3.2 Luminous Intensity Binning

Units are sorted by their luminous intensity (I_V) measured at 5mA. The bin code and corresponding range are:

• Bin Code J: 4.50 mcd (Min) to 7.10 mcd (Max)
• Bin Code K: 7.10 mcd to 11.2 mcd
• Bin Code L: 11.2 mcd to 18.0 mcd

Tolerance within each bin is ±15%.

3.3 Dominant Wavelength Binning

Units are sorted by their dominant wavelength (λ_d) measured at 5mA, which directly correlates to the shade of green. The bin code and corresponding range are:

• Bin Code B: 564.5 nm (Min) to 567.5 nm (Max)
• Bin Code C: 567.5 nm to 570.5 nm
• Bin Code D: 570.5 nm to 573.5 nm

Tolerance within each bin is ±1 nm.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (Fig.1, Fig.6), the provided data allows for analysis of key relationships.

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

The forward voltage (V_F) is specified at a test current of 5mA, with a typical range of 1.70V to 2.10V. Like all diodes, the LED's V_F has a positive temperature coefficient and will also increase slightly with higher drive currents. The specified V_F range must be considered when designing the driving circuit's voltage headroom.

4.2 Luminous Intensity vs. Forward Current

The luminous intensity is approximately proportional to the forward current over a significant range. The rated intensity values (4.5-18.0 mcd) are given at the standard test current of 5mA. Operating at the maximum continuous current of 30mA would yield significantly higher light output, but thermal management and lifetime considerations become critical.

4.3 Spectral Characteristics

The peak emission wavelength is typically 574 nm, with a spectral half-width of 15 nm. The dominant wavelength, which defines the perceived color, ranges from 564.5 nm to 573.5 nm depending on the bin. This places the emission firmly in the green region of the visible spectrum. The relationship between peak and dominant wavelength is influenced by the precise shape of the emission spectrum.

4.4 Thermal Derating

The datasheet explicitly states a derating factor of 0.4 mA/°C for the maximum continuous forward current above 25°C. This is a critical design parameter. For example, at an ambient temperature of 85°C, the maximum allowable continuous current is reduced by (85-25)*0.4 = 24 mA. Therefore, the maximum current at 85°C would be 30 mA - 24 mA = 6 mA. Exceeding this derated current increases the risk of accelerated degradation or failure.

5. Mechanical & Packaging Information

5.1 Package Dimensions

The device is an EIA-standard chip LED package. The key mechanical feature is its height of 0.55 mm. Detailed dimensional drawings would show the length, width, and placement of the cathode/anode terminals. All dimensions have a standard tolerance of ±0.10 mm unless otherwise specified on the drawing.

5.2 Polarity Identification

For surface-mount LEDs, polarity is typically indicated by a marking on the package, such as a dot, notch, or colored stripe near the cathode (negative) terminal. The tape and reel packaging is oriented to ensure correct polarity feeding into automated equipment. The cathode is usually connected to the larger internal lead frame or heat sink pad for better thermal performance.

5.3 Suggested Soldering Pad Layout

A recommended land pattern (footprint) for the printed circuit board (PCB) is provided. This pattern is designed to ensure reliable solder joint formation during reflow, provide adequate mechanical strength, and prevent solder bridging. It typically includes slightly larger pad areas than the device terminals to facilitate good solder fillets.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profiles

The datasheet provides two suggested infrared (IR) reflow profiles: one for normal (tin-lead) solder process and one for lead-free (Pb-free) solder process. The lead-free profile is mandatory when using SnAgCu solder paste. Key parameters for the lead-free process include:

• Pre-heat: A gradual ramp to avoid thermal shock.
• Soak/Pre-heat Time: Typically up to 120 seconds maximum.
• Peak Temperature: 260°C maximum.
• Time Above Liquidus: The time the component spends above the solder's melting point should be controlled, typically around 5 seconds maximum at peak temperature.

Adhering to these profiles is essential to prevent damage to the LED's plastic lens and internal wire bonds from excessive heat or thermal stress.

6.2 Wave Soldering & Hand Soldering

If wave soldering is used, recommendations include a pre-heat below 100°C for up to 60 seconds and exposure to a solder wave at a maximum of 260°C for no more than 10 seconds. For manual rework with a soldering iron, the tip temperature should not exceed 300°C, and contact time should be limited to 3 seconds per joint, for one repair cycle only.

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 room temperature for less than one minute. Unspecified chemical cleaners may damage the plastic lens or package material, leading to cracking or clouding.

6.4 Storage Conditions

LEDs are moisture-sensitive devices. For storage outside their original moisture-barrier packaging, it is critical to control the environment. Recommended storage conditions are at or below 30°C and 70% relative humidity. If stored out of the original bag for more than 672 hours (28 days), the components must be baked at approximately 60°C for at least 24 hours before being subjected to reflow soldering to remove absorbed moisture and prevent \"popcorning\" damage during the high-temperature reflow process.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The product is supplied in embossed carrier tape with a protective cover tape, wound onto 7-inch (178 mm) diameter reels. Standard packing quantity is 5,000 pieces per reel. For quantities that are not a multiple of 5,000, a minimum packing quantity of 500 pieces applies for the remainder. The packaging conforms to the ANSI/EIA 481-1-A-1994 standard, ensuring compatibility with automated equipment. The tape ensures correct component orientation and protects the devices during handling and shipping.

7.2 Part Number Structure

The part number LTST-C191KGKT-5A encodes specific attributes of the device. While the full corporate naming logic may be complex, it typically includes series identifiers (LTST-C191), color/performance codes (KGKT), and possibly bin or packaging codes (5A). The \"Water Clear\" lens description indicates the lens material is transparent, allowing the native green color of the AlInGaP chip to be seen directly, maximizing light output.

8. Application Recommendations

8.1 Typical Application Scenarios

• Status Indicators: Power-on, battery charging, network activity, or mode indicators in smartphones, tablets, laptops, and wearables.
• Backlighting: Edge-lit or direct backlighting for small LCD displays, keypads, or symbols on control panels, leveraging its thin profile.
• Consumer Electronics: Decorative or functional lighting in audio equipment, gaming consoles, and home appliances.
• Industrial Controls: Status and fault indicators on human-machine interfaces (HMIs), sensors, and control units.

8.2 Circuit Design Considerations

Current Drive Method: An LED is a current-driven device. To ensure uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use a individual current-limiting resistor in series with each LED (Circuit Model A). Relying on the natural I-V characteristics of the LEDs to balance current in a simple parallel connection (Circuit Model B) is not recommended, as small variations in forward voltage will cause significant differences in current and, therefore, brightness between devices.

Electrostatic Discharge (ESD) Protection: The semiconductor junction is susceptible to damage from electrostatic discharge. Handling precautions must be observed: use grounded wrist straps and work surfaces, store components in anti-static materials, and employ ionizers to neutralize static charges that can build up on the plastic lens during handling.

8.3 Thermal Management

Although small, the LED generates heat at the junction. The power dissipation limit (75 mW) and current derating factor (0.4 mA/°C) are directly related to thermal performance. In high-ambient-temperature environments or when driving at high currents, attention must be paid to the PCB layout. Using adequate copper area (thermal pads) connected to the LED's terminals, especially the cathode if it is thermally enhanced, helps conduct heat away from the device and into the PCB, maintaining lower junction temperatures and ensuring long-term reliability.

9. Technical Comparison & Differentiation

The primary differentiator of this LED is its combination of ultra-low height (0.55mm) and high brightness from AlInGaP technology. Compared to older technology like GaP (Gallium Phosphide) green LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in brighter light output for the same drive current. Compared to some other ultra-thin packages, the use of a standard EIA footprint ensures broad compatibility with existing PCB designs and assembly processes without requiring specialized tooling. The wide 130-degree viewing angle is another advantageous feature for applications where the indicator needs to be visible from off-axis viewpoints.

10. Frequently Asked Questions (FAQs)

10.1 What is the difference between peak wavelength and dominant wavelength?

Peak Wavelength (λ_P): The specific wavelength where the optical power output of the LED is physically at its maximum. It's a property of the semiconductor material and epitaxy. Dominant Wavelength (λ_d): A calculated value that represents the single wavelength of monochromatic light that would appear to have the same color as the LED's actual broad-spectrum output, according to the human eye's color perception (CIE standard). λ_d is the parameter that defines the \"color\" (e.g., green) for specification and binning purposes.

10.2 Why is a series resistor necessary for each LED in parallel?

LEDs have a non-linear I-V characteristic. A small difference in forward voltage (V_F)—common due to manufacturing variations—will cause a large difference in current when two LEDs are connected directly in parallel to a voltage source. The LED with the slightly lower V_F will draw disproportionately more current, becoming brighter and potentially overheating, while the other remains dim. A series resistor for each LED provides negative feedback, stabilizing the current and ensuring matched brightness despite V_F variations.

10.3 Can I drive this LED at its maximum continuous current of 30mA?

You can, but you must carefully consider the thermal environment. At 30mA and a typical V_F of 2.0V, the power dissipation is 60mW, which is close to the absolute maximum of 75mW. Furthermore, the current must be derated for ambient temperatures above 25°C. At 30mA, there is very little margin. For reliable long-term operation, it is often prudent to drive the LED at a lower current, such as the 5mA or 10-20mA range, which still provides good brightness while significantly reducing thermal stress and improving lifetime.

10.4 How critical is the baking procedure before soldering?

It is very critical if the components have been exposed to ambient humidity outside their sealed moisture-barrier bag for more than the specified time (28 days/672 hours). Plastic packages can absorb moisture. During the rapid heating of reflow soldering, this trapped moisture can vaporize explosively, causing internal delamination, cracks in the package or lens, or broken wire bonds—a failure known as \"popcorning.\" Baking at 60°C for 24 hours safely drives out this absorbed moisture, preventing such damage.

11. Design-in Case Study

Scenario: Designing a status indicator for a new, ultra-thin Bluetooth speaker. The indicator must be bright enough to see in daylight, have a wide viewing angle, and fit within a total enclosure thickness of less than 4mm.

Component Selection: The LTST-C191KGKT-5A is chosen primarily for its 0.55mm height, allowing ample space for the enclosure wall and diffuser. The AlInGaP technology ensures sufficient brightness (selecting Bin L for highest intensity). The 130-degree viewing angle means the light will be visible from almost any angle around the speaker.

Circuit Design: The LED is driven by a GPIO pin of the system's microcontroller, which outputs 3.3V. A series resistor is calculated. Targeting a drive current of 10mA for a good balance of brightness and power/heat: R = (V_source - V_F) / I_F. Using a typical V_F of 2.0V, R = (3.3V - 2.0V) / 0.01A = 130 Ohms. A standard 130Ω resistor is placed in series with the LED on the PCB.

PCB Layout: The recommended solder pad layout from the datasheet is used. Additional thermal relief is added by connecting the cathode pad to a small copper pour on the PCB to help dissipate heat, as the speaker's internal ambient temperature might rise during operation.

Assembly: The LEDs are ordered on tape and reel for automated assembly. The contract manufacturer is provided with the lead-free reflow profile from the datasheet to ensure proper soldering without thermal damage.

12. Technology Principles

The LED is based on a semiconductor p-n junction made from Aluminum Indium Gallium Phosphide (AlInGaP) materials. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the active region where they recombine. This recombination process releases energy in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material, which is engineered by adjusting the ratios of Aluminum, Indium, Gallium, and Phosphorus during crystal growth. AlInGaP is particularly efficient for producing light in the red, orange, yellow, and green parts of the spectrum. The \"water clear\" lens is typically made of epoxy or silicone that is molded directly over the chip and wire bonds, providing environmental protection, mechanical support, and optical shaping to achieve the desired viewing angle.

13. Industry Trends

The trend in indicator LEDs continues toward miniaturization and higher efficiency. Package heights are constantly being reduced to enable thinner end products. There is also a drive toward higher brightness (lumens per watt) to achieve required light levels at lower drive currents, which saves system power and simplifies thermal design. While AlInGaP dominates the green-yellow-red spectrum for discrete indicators, InGaN (Indium Gallium Nitride) technology is prevalent for blue, white, and true green (often called \"pure green\\