Orange SMD LED LTST-S220KFKT Datasheet - AlInGaP Chip - 20mA - 90mcd - English Technical Document

1. Product Overview

The LTST-S220KFKT is a high-brightness, side-looking Surface-Mount Device (SMD) LED. It utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor chip, which is known for producing efficient and bright orange light. This component is designed for automated assembly processes and is compatible with standard infrared reflow soldering techniques, making it suitable for high-volume manufacturing. Its primary application is as an indicator light or backlight source in various electronic devices where space is constrained and a side-emitting profile is advantageous.

1.1 Core Advantages

• High Brightness: The AlInGaP technology delivers high luminous intensity, with a typical value of 90 millicandelas (mcd) at a forward current of 20mA.
• Wide Viewing Angle: Features a 130-degree viewing angle (2θ1/2), ensuring good visibility from various perspectives.
• Automation Friendly: Supplied on 8mm tape mounted on 7-inch reels, compatible with automatic pick-and-place equipment for efficient PCB assembly.
• Robust Construction: Designed to withstand standard lead-free (Pb-free) infrared reflow soldering profiles, with a peak temperature tolerance of 260°C for 10 seconds.
• Compliance: The product meets RoHS (Restriction of Hazardous Substances) directives.

2. In-Depth Technical Parameter Analysis

This section provides a detailed breakdown of the key electrical, optical, and thermal parameters that define the LED's performance and operational limits.

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 for extended periods is not recommended.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can safely dissipate as heat.
• Peak Forward Current (IFP): 80 mA. This is the maximum allowable pulsed current, typically specified under conditions like a 1/10 duty cycle and 0.1ms pulse width. It is used for brief, high-intensity flashes.
• Continuous Forward Current (IF): 30 mA DC. This is the maximum steady-state current for continuous operation.
• Reverse Voltage (VR): 5 V. Exceeding this voltage in reverse bias can damage the LED's PN junction.
• Operating Temperature Range (Topr): -30°C to +85°C. The ambient temperature range within which the LED is designed to function correctly.
• Storage Temperature Range (Tstg): -40°C to +85°C. The temperature range for safe storage when the device is not powered.

2.2 Electro-Optical Characteristics

Measured at a standard ambient temperature of 25°C, these parameters define the typical performance of the LED under normal operating conditions.

• Luminous Intensity (Iv): Ranges from a minimum of 45.0 mcd to a typical 90.0 mcd at IF=20mA. This measures the perceived brightness of the light output by the human eye.
• Forward Voltage (VF): Typically 2.4V, with a maximum of 2.4V at IF=20mA. This is the voltage drop across the LED when it is conducting current.
• Peak Wavelength (λP): 611 nm. This is the wavelength at which the optical power output is at its maximum. For this orange LED, it falls in the orange-red part of the spectrum.
• Dominant Wavelength (λd): 605 nm. This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color of the light.
• Spectral Line Half-Width (Δλ): 17 nm. This indicates the spectral purity; a smaller value means a more monochromatic (pure color) light output.
• Reverse Current (IR): 10 μA maximum at VR=5V. This is the small leakage current that flows when the LED is reverse-biased within its maximum rating.

3. Binning System Explanation

To ensure consistency in brightness across production batches, LEDs are sorted into bins based on their measured luminous intensity. The LTST-S220KFKT uses a binning system with the following codes and ranges, measured at 20mA. The tolerance for each intensity bin is +/-15%.

• Bin Code P: 45.0 - 71.0 mcd
• Bin Code Q: 71.0 - 112.0 mcd
• Bin Code R: 112.0 - 180.0 mcd
• Bin Code S: 180.0 - 280.0 mcd

This allows designers to select LEDs from a specific bin for applications requiring uniform brightness levels.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet, their implications are critical for design.

4.1 Current vs. Luminous Intensity (I-Iv Curve)

The light output (luminous intensity) of an LED is directly proportional to the forward current flowing through it, up to a point. Operating above the recommended continuous current (30mA) can lead to excessive heat, reduced lifespan, and color shift. The pulsed current rating (80mA) allows for short bursts of higher brightness without thermal damage.

4.2 Temperature Dependence

LED performance is temperature-sensitive. As the junction temperature increases:

• Luminous Intensity Decreases: Light output typically drops. The datasheet's specifications are at 25°C; at higher operating temperatures, the output will be lower.
• Forward Voltage Decreases: VF has a negative temperature coefficient.
• Wavelength Shifts: The peak and dominant wavelengths may shift slightly, potentially affecting the perceived color.

Proper thermal management (e.g., adequate PCB copper area for heat sinking) is essential to maintain performance and reliability.

4.3 Spectral Distribution

The spectral curve shows the light intensity across different wavelengths. The peak at 611nm and the 17nm half-width confirm this is an orange LED with a relatively narrow spectral bandwidth, providing a saturated color.

5. Mechanical and Package Information

The LED features a side-looking package design, meaning the primary light emission is from the side of the component rather than the top. This is ideal for edge-lighting applications.

5.1 Package Dimensions and Polarity

The component follows an EIA standard package outline. Key dimensional tolerances are typically ±0.10mm. The cathode (negative terminal) is usually indicated by a marking on the package, such as a notch, dot, or trimmed lead. The datasheet includes a detailed dimensional drawing with suggested solder pad layout to ensure proper alignment and solder joint formation during reflow.

5.2 Suggested Solder Pad Design

A recommended land pattern (solder pad footprint) is provided to facilitate good soldering yield and mechanical stability. Following this design helps prevent issues like tombstoning (one end lifting off the pad) or insufficient solder joints.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Profile

The LED is compatible with lead-free (Pb-free) infrared reflow processes. A suggested profile is provided, adhering to JEDEC standards. Key parameters include:

• Preheat: 150-200°C for up to 120 seconds to gradually heat the board and activate the solder paste flux.
• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus (TAL): The time the solder joint spends above its melting point should be sufficient for proper wetting but not excessive to avoid thermal stress on the LED. The profile suggests a peak temperature time of 10 seconds maximum.

The component can withstand this reflow process a maximum of two times.

6.2 Hand Soldering

If hand soldering is necessary, use a temperature-controlled iron set to a maximum of 300°C. Limit the contact time to 3 seconds per joint, and solder only once to prevent thermal damage to the plastic package and the internal wire bonds.

6.3 Cleaning

If post-solder cleaning is required, use only specified solvents. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable. Avoid using aggressive or unspecified chemicals that could damage the plastic lens or package.

6.4 Storage and Handling

• ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Use wrist straps, anti-static mats, and properly grounded equipment during handling.
• Moisture Sensitivity: While the datasheet indicates the package is sealed, standard MSL (Moisture Sensitivity Level) precautions apply for SMD components after the original packaging is opened. If exposed to ambient humidity, a bake-out (e.g., 60°C for 20 hours) may be required before reflow to prevent "popcorning" (package cracking due to vapor pressure during heating).
• Storage Conditions: For opened packages, store at ≤30°C and ≤60% relative humidity. Use within one week is recommended for best results.

7. Packaging and Ordering Information

The standard packaging format is crucial for automated assembly.

• Tape and Reel: Components are placed in 8mm wide embossed carrier tape.
• Reel Size: 7 inches in diameter.
• Quantity per Reel: 4000 pieces.
• Packing Notes: Empty pockets are sealed with cover tape. The maximum number of consecutive missing components is two. Minimum order quantity for remainders is 500 pieces. Packaging conforms to ANSI/EIA-481 specifications.

8. Application Notes and Design Considerations

8.1 Typical Application Circuits

LEDs are current-driven devices. To ensure consistent brightness and longevity, they must be driven with a constant current or with a current-limiting resistor in series when using a voltage source.

Example Calculation for Series Resistor (using a 5V supply and typical VF=2.4V, IF=20mA):
Resistor Value, R = (Vsupply - VF) / IF = (5V - 2.4V) / 0.020A = 130 Ohms.
Resistor Power Rating, P = (Vsupply - VF) * IF = (2.6V) * 0.020A = 0.052W. A standard 1/8W (0.125W) or 1/10W resistor is sufficient.

For multiple LEDs, connecting them in series (if the supply voltage is high enough) is preferable to parallel connections, as it ensures identical current through each LED, promoting uniform brightness.

8.2 Design Considerations

• Thermal Management: Ensure the PCB layout provides adequate thermal relief, especially if operating near maximum current ratings. Connecting the thermal pad (if present) to a ground plane can help dissipate heat.
• Current Limiting: Never connect an LED directly to a voltage source without a current-limiting mechanism.
• Reverse Voltage Protection: Avoid applying reverse bias. In circuits where reverse voltage is possible (e.g., AC coupling), consider adding a protection diode in parallel with the LED (cathode-to-cathode, anode-to-anode).

9. Technical Comparison and Differentiation

The LTST-S220KFKT differentiates itself through its combination of AlInGaP technology and side-viewing package. Compared to older GaAsP or GaP LEDs, AlInGaP offers significantly higher efficiency and brightness for orange/red colors. The side-looking form factor provides design flexibility for applications where light needs to be directed horizontally across a surface, such as in button backlighting, status indicators on the edge of a device, or light guides.

10. Frequently Asked Questions (FAQs)

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

Peak wavelength (λP) is the physical wavelength where the LED emits the most optical power. Dominant wavelength (λd) is a calculated value based on human color perception (CIE chart) that best represents the color we see. They are often close but not identical.

10.2 Can I drive this LED with a 3.3V supply?

Yes. Using the typical VF of 2.4V at 20mA, a series resistor would be calculated as R = (3.3V - 2.4V) / 0.020A = 45 Ohms. Ensure the resistor power rating is adequate (0.9V * 0.02A = 0.018W).

10.3 Why is there a peak current rating much higher than the continuous current?

The peak current rating (80mA) is for very short pulses (0.1ms). This allows the LED to produce a much brighter flash for signaling purposes without the junction temperature rising to damaging levels, as there is insufficient time for heat to accumulate. For constant illumination, the continuous current (30mA) must not be exceeded.

10.4 How do I interpret the bin code?

The bin code (e.g., P, Q, R, S) on the reel label or packaging indicates the luminous intensity range of the LEDs inside. Selecting from a single bin ensures consistent brightness in your product. For example, Bin S LEDs will be significantly brighter than Bin P LEDs when driven at the same current.

11. Practical Application Example

Scenario: Designing a low-battery indicator for a portable device.
The LTST-S220KFKT is an excellent choice. Its orange color is a common warning indicator. The side-viewing package allows it to be mounted on the edge of the PCB, directing light towards a translucent window on the device casing. Driven at 15-20mA via a GPIO pin and a series resistor from the device's 3.3V rail, it provides a clear, bright signal. The wide 130-degree viewing angle ensures the indicator is visible even when the device is viewed from an angle. Its compatibility with reflow soldering allows it to be assembled alongside all other SMD components in one pass, reducing manufacturing cost.

12. Operating Principle

An LED is a semiconductor diode. When a forward voltage exceeding its bandgap voltage is applied, electrons and holes recombine in the active region (the AlInGaP chip in this case). This recombination releases energy in the form of photons (light). The specific material composition of the semiconductor (AlInGaP) determines the bandgap energy, which in turn dictates the wavelength (color) of the emitted light—in this instance, orange. The side-looking package incorporates a molded plastic lens that shapes and directs the emitted light from the chip sideways.

13. Technology Trends

The use of AlInGaP materials represents an established and mature technology for producing high-efficiency red, orange, and yellow LEDs. Ongoing development in the broader LED industry focuses on increasing efficiency (lumens per watt), improving color rendering, and enabling higher power densities. For indicator-type LEDs like the LTST-S220KFKT, trends include further miniaturization, the development of even wider viewing angles, and enhanced compatibility with demanding assembly processes. The drive towards higher automation and reliability in electronics manufacturing continues to make robust, reflow-solderable SMD LEDs the standard choice over through-hole components.