SMD LED LTST-E212KRKGWT Datasheet - Dimensions 2.0x1.25x0.8mm - Voltage 1.8-2.5V - Power 75mW - Red/Green Colors - English Technical Document

1. Product Overview

The LTST-E212KRKGWT is a compact, surface-mount LED designed for automated printed circuit board assembly in space-constrained applications. It features a diffused lens and is available with two distinct light source technologies: AlInGaP for red emission and InGaN for green emission. This dual-color capability within a single package footprint makes it versatile for status indication, backlighting, and signage where multiple colors are required from a common component location.

1.1 Core Advantages

• Miniaturized Form Factor: The small package size is ideal for high-density PCB layouts found in modern portable and consumer electronics.
• Dual Color Source: Offers design flexibility by providing red and green options with compatible pin assignments, simplifying inventory and PCB design for bi-color applications.
• Automation Compatibility: Packaged in 8mm tape on 7-inch reels, it is fully compatible with high-speed automatic pick-and-place equipment, streamlining manufacturing.
• Robust Process Compatibility: Designed to withstand standard infrared (IR) reflow soldering processes, including those required for lead-free (Pb-free) solder assembly.
• Environmental Compliance: The product meets RoHS (Restriction of Hazardous Substances) directives.

1.2 Target Markets and Applications

This LED is suitable for a broad range of electronic equipment. Primary application areas include telecommunications devices (cordless and cellular phones), portable computing (notebooks, tablets), network systems, home appliances, and indoor signage or display panels. Its reliability and small size make it a preferred choice for consumer and industrial electronics where consistent performance and efficient assembly are critical.

2. In-Depth Technical Parameter Analysis

The following section provides a detailed, objective interpretation of the key electrical and optical parameters specified for the LTST-E212KRKGWT LED, measured at an ambient temperature (Ta) of 25°C.

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.

• Power Dissipation (Pd): 75 mW for both red and green variants. This parameter limits the total electrical power (Forward Current * Forward Voltage) that can be converted into light and heat within the LED chip.
• Peak Forward Current (I_FP): 80 mA, permissible only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). Exceeding this in DC operation will likely cause overheating.
• DC Forward Current (I_F): 30 mA. This is the recommended maximum continuous current for reliable long-term operation.
• Temperature Range: Operating and storage temperature range is -40°C to +100°C, indicating suitability for environments with wide temperature swings.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters under standard test conditions (I_F = 20mA).

• Luminous Intensity (I_V): The typical light output is 75 mcd for the red LED and 65 mcd for the green LED, with a minimum guaranteed value of 28 mcd for both. This intensity is measured using a sensor filtered to match the human eye's photopic response.
• Viewing Angle (2θ_1/2): A typical value of 120 degrees is specified. This wide viewing angle, characteristic of a diffused lens, ensures good visibility over a broad area, making it suitable for panel indicators.
• Wavelength:
  • Red (AlInGaP): Peak Emission Wavelength (λ_P) is typically 639 nm. Dominant Wavelength (λ_d) is typically 631 nm.
  • Green (InGaN): Peak Emission Wavelength (λ_P) is typically 574 nm. Dominant Wavelength (λ_d) is typically 566 nm.
  The slight difference between peak and dominant wavelength is normal and relates to the shape of the emission spectrum.
• Spectral Line Half-Width (Δλ): Typically 20 nm for both colors, indicating the spectral purity or bandwidth of the emitted light.
• Forward Voltage (V_F): Ranges from 1.8V (min) to 2.5V (max) at 20mA. The typical value for design should be considered around the midpoint, but circuits must accommodate the full range. A tolerance of ±0.1V is noted.
• Reverse Current (I_R): Maximum of 10 µA at a Reverse Voltage (V_R) of 5V. It is crucial to note that this device is not designed for reverse operation; this test is for quality verification only.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-E212KRKGWT uses separate bins for luminous intensity and, for the green version, dominant wavelength.

3.1 Luminous Intensity (I_V) Binning

Both red and green LEDs share the same intensity bin codes, measured in millicandelas (mcd) at 20mA. Each bin has an 11% tolerance.

• Bin N: 28.0 – 45.0 mcd
• Bin P: 45.0 – 71.0 mcd
• Bin Q: 71.0 – 112.0 mcd
• Bin R: 112.0 – 180.0 mcd

For example, an LED labeled with Bin Q for intensity will have a typical output between 71 and 112 mcd. Designers should specify the required bin to guarantee minimum brightness levels in their application.

3.2 Dominant Wavelength (WD) Binning for Green

Only the green LED has specified wavelength bins, measured in nanometers (nm) at 20mA, with a ±1 nm tolerance per bin.

• Bin G1: 566.0 – 569.0 nm
• Bin G2: 569.0 – 572.0 nm
• Bin G3: 572.0 – 575.0 nm

This binning allows for tighter control over the exact shade of green, which can be important for color-matching in multi-LED displays or specific aesthetic requirements.

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet (e.g., Figure 1 for spectral distribution, Figure 6 for viewing angle), their general implications are analyzed here.

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

The I-V characteristic of an LED is non-linear. For the LTST-E212KRKGWT, at the typical operating current of 20mA, the forward voltage falls between 1.8V and 2.5V. The curve will show a sharp increase in current once the forward voltage exceeds the diode's turn-on threshold. This necessitates the use of a current-limiting resistor or constant-current driver in series with the LED when powered from a voltage source to prevent thermal runaway.

4.2 Luminous Intensity vs. Forward Current

Light output (luminous intensity) is generally proportional to forward current within the device's operating range. However, efficiency may drop at very high currents due to increased heat. Operating at the recommended 20mA ensures optimal balance between brightness and longevity.

4.3 Spectral Distribution

The referenced spectral graphs would show a single, dominant peak for each color (around 639nm for red, 574nm for green) with a typical half-width of 20nm. The AlInGaP red LED typically has a narrower spectrum compared to some other red technologies, while the InGaN green spectrum is standard for its type. The diffused lens slightly broadens the angular distribution of these wavelengths but does not significantly alter the peak spectral output.

5. Mechanical & Package Information

5.1 Package Dimensions and Polarity

The SMD package has a nominal footprint. Critical dimensions include the body size and lead spacing. The pin assignment is crucial for correct orientation:

• Red LED (AlInGaP): Anode and cathode are assigned to pins 1 and 3.
• Green LED (InGaN): Anode and cathode are assigned to pins 1 and 4.

This difference means a single PCB footprint can accommodate either color, but the driving circuit must connect to the correct pins. The package outline drawing (implied in the datasheet) should always be consulted for exact dimensions and pad positioning.

5.2 Recommended PCB Attachment Pad Layout

A suggested land pattern is provided to ensure proper soldering and mechanical stability. The pad design typically includes thermal reliefs to facilitate soldering while providing sufficient copper area for heat dissipation and strong adhesion. Following this recommendation helps prevent tombstoning (one end lifting during reflow) and ensures reliable solder joints.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Profile

The datasheet references J-STD-020B for lead-free process conditions. A generic profile is suggested with key limits:

• Pre-heat: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds to slowly ramp temperature and activate flux.
• Peak Temperature: Maximum 260°C. The time above liquidus (e.g., 217°C) should be controlled per solder paste specifications.
• Soldering Time at Peak: Maximum 10 seconds, and reflow should not be performed more than twice.

It is emphasized that the optimal profile depends on the specific PCB assembly, and characterization is necessary.

6.2 Hand Soldering

If manual soldering is necessary, a soldering iron temperature should not exceed 300°C, and contact time should be limited to a maximum of 3 seconds for a single operation only. Excessive heat or time can damage the LED package or the internal wire bonds.

6.3 Storage and Handling

The LEDs are moisture-sensitive. Key storage rules include:

• Sealed Package: Store at ≤ 30°C and ≤ 70% RH. Use within one year of the dry-pack date.
• Opened Package: For components removed from the moisture barrier bag, the ambient should be ≤ 30°C and ≤ 60% RH.
• Floor Life: It is recommended to complete IR reflow within 168 hours (7 days) after opening the original packaging.
• Rebaking: If the exposure time exceeds 168 hours, a bake at approximately 60°C for at least 48 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" (package cracking during reflow).

6.4 Cleaning

If post-solder cleaning is required, only specified alcohol-based solvents like ethyl alcohol or isopropyl alcohol should be used at normal temperature for less than one minute. Unspecified chemicals may damage the plastic lens or package material.

7. Packaging and Ordering Information

7.1 Tape and Reel Specifications

The product is supplied standard in embossed carrier tape with a protective cover tape, wound on 7-inch (178mm) diameter reels. Standard reel quantity is 3000 pieces. A minimum packing quantity of 500 pieces is available for remainder orders. The tape and reel dimensions conform to ANSI/EIA-481 specifications, ensuring compatibility with standard automated assembly equipment feeders.

8. Application Notes and Design Considerations

8.1 Typical Application Circuits

The most common drive method is a voltage source (V_CC) in series with a current-limiting resistor (R_S). The resistor value can be calculated using Ohm's Law: R_S = (V_CC - V_F) / I_F. For example, with a 5V supply, a typical V_F of 2.2V, and a desired I_F of 20mA: R_S = (5 - 2.2) / 0.02 = 140 Ω. The nearest standard value (e.g., 150 Ω) would be chosen, slightly reducing the current. The power rating of the resistor should be at least I_F² * R_S.

8.2 Thermal Management

Although the power dissipation is low (75mW max), proper thermal design extends LED life. Ensure the recommended PCB pad connects to adequate copper area to act as a heat sink. Avoid operating at the absolute maximum current (30mA DC) continuously in high ambient temperatures, as this accelerates lumen depreciation.

8.3 Reverse Voltage Protection

As the device is not designed for reverse bias, incorporating protection is wise in circuits where reverse voltage is possible (e.g., in back-to-back LED configurations or with inductive loads). A simple diode in parallel with the LED (cathode to anode) can provide this protection.

9. Technical Comparison and Differentiation

The LTST-E212KRKGWT's primary differentiation lies in its dual-source (AlInGaP/InGaN), dual-color capability within a standardized SMD package. Compared to single-color LEDs, it offers design flexibility. Against other bi-color LEDs, its use of mature, efficient semiconductor materials (AlInGaP for red, InGaN for green) typically results in good luminous efficacy and stable performance over temperature. The wide 120-degree viewing angle from its diffused lens is a key feature versus narrow-angle LEDs, making it superior for applications requiring wide-area visibility.

10. Frequently Asked Questions (FAQs)

10.1 Can I drive this LED directly from a 3.3V or 5V microcontroller pin?

Answer: No, not directly. Microcontroller GPIO pins are voltage sources with limited current sourcing/sinking capability (often 20-25mA). Connecting an LED directly risks exceeding both the LED's maximum current and the GPIO pin's rating, potentially damaging both. Always use a series current-limiting resistor or a transistor driver circuit.

10.2 What is the difference between Peak Wavelength and Dominant Wavelength?

Answer: Peak Wavelength (λ_P) is the single wavelength at which the spectral power distribution is maximum. Dominant Wavelength (λ_d) is the single wavelength of monochromatic light that, when combined with a specified white reference, matches the perceived color of the LED. λ_d is more closely related to the human perception of color.

10.3 Why are the storage conditions so strict?

Answer: The plastic LED package can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating internal pressure that can delaminate the package or crack the die (\"popcorning\"). The strict storage and baking procedures control moisture content to prevent this failure mode.

11. Practical Design Case Study

Scenario: Designing a status indicator panel for a network router requiring red (fault/error) and green (operational/ready) indicators in a very compact space.

Implementation: Using the LTST-E212KRKGWT allows a single PCB footprint to be used for both status colors. The PCB layout includes the recommended pad pattern. The microcontroller firmware controls two GPIO pins, each connected through a suitable current-limiting resistor (e.g., 150Ω for 5V supply) to pin 1 (common anode) of the LED. One GPIO drives pin 3 (red cathode), and another drives pin 4 (green cathode). This design halves the required PCB space compared to using two separate single-color LEDs and simplifies assembly.

12. Operational Principle

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction, electrons from the n-type region recombine with holes from the p-type region within the active layer. This recombination 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 used. The LTST-E212KRKGWT utilizes AlInGaP (Aluminum Indium Gallium Phosphide) for red light and InGaN (Indium Gallium Nitride) for green light, each material chosen for its efficiency and color purity in its respective spectrum.

13. Technology Trends

The general trend in SMD LEDs like this one is towards higher luminous efficacy (more light output per watt of electrical input), improved color consistency through tighter binning, and further miniaturization enabling even higher density PCB designs. There is also a growing emphasis on enhanced reliability under higher temperature and humidity conditions to meet automotive and industrial standards. The underlying material science continues to advance, with ongoing research into new semiconductor compounds and nanostructures to push efficiency limits and enable new colors.