SMD LED LTST-C190KEKT Datasheet - AlInGaP Red - 130° Viewing Angle - 1.7-2.5V - 30mA - English Technical Document

1. Product Overview

The LTST-C190KEKT is a surface-mount device (SMD) LED lamp designed for automated printed circuit board (PCB) assembly. It belongs to a family of miniature LEDs intended for space-constrained applications across a broad spectrum of electronic equipment.

1.1 Core Advantages and Target Market

This LED offers several key advantages that make it suitable for modern electronics manufacturing. Its primary features include compliance with RoHS (Restriction of Hazardous Substances) directives, utilization of an ultra-bright AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor chip for efficient red light emission, and packaging on 8mm tape wound onto 7-inch diameter reels compatible with standard automated pick-and-place equipment. The device is also designed to be compatible with infrared (IR) reflow soldering processes, which is the industry standard for high-volume SMD assembly.

The target applications are diverse, reflecting the component's versatility. Key markets include telecommunications equipment (e.g., cordless and cellular phones), office automation devices (e.g., notebook computers, network systems), home appliances, and indoor signage or display applications. Specific functional uses within these devices encompass keypad or keyboard backlighting, status indication, micro-displays, and signal or symbol illumination.

2. Technical Parameters: In-Depth Objective Interpretation

The performance of the LTST-C190KEKT is defined by a set of absolute maximum ratings and standard electrical/optical characteristics, all specified at an ambient temperature (Ta) of 25°C.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They should not be exceeded under any operating conditions.

• Power Dissipation (Pd): 75 mW. This is the maximum amount of power the LED package can dissipate as heat.
• Peak Forward Current (I_F(PEAK)): 80 mA. This is the maximum instantaneous forward current, permissible only under pulsed conditions with a 1/10 duty cycle and a 0.1ms pulse width.
• DC Forward Current (I_F): 30 mA. This is the maximum continuous forward current for reliable long-term operation.
• Reverse Voltage (V_R): 5 V. Applying a reverse voltage exceeding this value can cause junction breakdown.
• Operating & Storage Temperature Range: -55°C to +85°C.
• Infrared Soldering Condition: Withstands 260°C peak temperature for 10 seconds, which is typical for lead-free (Pb-free) solder reflow profiles.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured under standard test conditions.

• Luminous Intensity (I_V): 28.0 to 112.0 mcd (millicandela) at a forward current (I_F) of 20mA. The intensity is measured using a sensor and filter combination that approximates the photopic (CIE) human eye response curve.
• Viewing Angle (2θ_1/2): 130 degrees. This is the full angle at which the luminous intensity drops to half of its value measured on the central axis (0°). A wide viewing angle like this is suitable for applications requiring broad, diffuse illumination rather than a focused beam.
• Peak Emission Wavelength (λ_P): 632.0 nm (nanometers). This is the wavelength at which the spectral power output is highest.
• Dominant Wavelength (λ_d): 617.0 to 631.0 nm at I_F=20mA. This is derived from the CIE chromaticity diagram and represents the single wavelength that best describes the perceived color of the light. The range indicates potential variation between individual units.
• Spectral Line Half-Width (Δλ): 20 nm. This indicates the spectral bandwidth, measured as the full width at half maximum (FWHM) of the emission peak.
• Forward Voltage (V_F): 1.7 to 2.5 V at I_F=20mA. This is the voltage drop across the LED when operating. The range accounts for normal manufacturing variances in the semiconductor material.
• Reverse Current (I_R): 10 μA (microamperes) maximum at a reverse voltage (V_R) of 5V.

3. Binning System Explanation

To ensure consistency in brightness for end products, LEDs are often sorted into performance bins after manufacturing.

3.1 Luminous Intensity Bin Code

For the LTST-C190KEKT in red color, luminous intensity is categorized into bins as follows, measured at 20mA:

• Bin Code N: Minimum 28.0 mcd, Maximum 45.0 mcd.
• Bin Code P: Minimum 45.0 mcd, Maximum 71.0 mcd.
• Bin Code Q: Minimum 71.0 mcd, Maximum 112.0 mcd.

A tolerance of +/-15% is applied to the limits of each bin. This binning allows designers to select LEDs with a guaranteed minimum brightness for their application, which is critical for achieving uniform appearance in multi-LED arrays.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., on page 5/11), their typical 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 AlInGaP material used here, the typical forward voltage ranges from 1.7V to 2.5V at 20mA. The curve shows that a small increase in voltage beyond the turn-on threshold leads to a rapid increase in current. Therefore, LEDs must be driven by a current-limited source, not a constant voltage source, to prevent thermal runaway and destruction.

4.2 Luminous Intensity vs. Forward Current

The light output (luminous intensity) is approximately proportional to the forward current over a significant operating range. However, efficiency may drop at very high currents due to increased heat generation within the chip. Operating at or below the recommended 20mA test condition ensures optimal performance and longevity.

4.3 Spectral Distribution

The emission spectrum is centered around 632 nm (peak) with a half-width of approximately 20 nm. This defines a relatively pure red color. The dominant wavelength (617-631 nm) determines the perceived hue. Variations within this range are normal and are managed through the manufacturing process.

5. Mechanical and Package Information

5.1 Package Dimensions and Polarity Identification

The LED is housed in a standard SMD package. The lens color is water clear, while the light source emits red light from the AlInGaP chip. All dimensions are provided in millimeters with a standard tolerance of ±0.1 mm unless otherwise specified. The package includes features for correct orientation (polarity) during placement, typically indicated by a marking on the body or an asymmetric shape. Correct polarity is essential for the device to function.

5.2 Recommended PCB Attachment Pad Layout

A recommended land pattern (footprint) for the PCB is provided to ensure proper solder joint formation, mechanical stability, and thermal management during and after the reflow process. Adhering to this design is critical for achieving reliable solder connections and managing heat dissipation from the LED junction through the PCB traces.

6. Soldering and Assembly Guidelines

6.1 Reflow Soldering Parameters

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

• Pre-heat: 150°C to 200°C.
• Pre-heat Time: Maximum 120 seconds.
• Peak Temperature: Maximum 260°C.
• Time Above Liquidus (at peak): Maximum 10 seconds. The device can withstand this profile a maximum of two times.

It is emphasized that the optimal profile depends on the specific PCB design, components, solder paste, and oven. Characterization for the specific application is recommended.

6.2 Hand Soldering (Soldering Iron)

If hand soldering is necessary, extreme care must be taken:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per pad.
• Frequency: This should be performed only once to avoid thermal stress.

6.3 Storage Conditions

Proper storage is vital to maintain solderability and device integrity.

• Sealed Package (Moisture Barrier Bag): Store at ≤30°C and ≤90% Relative Humidity (RH). The shelf life is one year when stored in the original moisture-proof bag with desiccant.
• Opened Package: The ambient should not exceed 30°C or 60% RH. Components removed from their original packaging should be IR-reflowed within one week (corresponding to Moisture Sensitivity Level 3, MSL 3). For longer storage outside the original bag, use a sealed container with desiccant or a nitrogen desiccator. Components stored open for more than one week require baking at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.4 Cleaning

If cleaning after soldering is required, 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 package or lens.

7. Application Suggestions and Design Considerations

7.1 Drive Circuit Design

An LED is a current-operated device. To ensure consistent brightness, especially when multiple LEDs are used in parallel, each LED should have its own current-limiting resistor connected in series. The resistor value (R) is calculated using Ohm's Law: R = (V_supply - V_F) / I_F, where V_F is the forward voltage of the LED at the desired current I_F. Using a common resistor for multiple parallel LEDs is not recommended due to variations in individual V_F, which can lead to significant differences in current and thus brightness.

7.2 Thermal Management

While the power dissipation is relatively low (75mW max), proper thermal design extends LED life and maintains stable light output. Ensuring the recommended PCB pad layout is used helps conduct heat away from the LED junction. Operating the LED at currents lower than the maximum 30mA DC rating will reduce junction temperature and improve long-term reliability.

7.3 Electrostatic Discharge (ESD) Precautions

LEDs are sensitive to electrostatic discharge and voltage surges. Handling precautions are necessary to prevent latent or catastrophic damage. It is recommended to use a grounded wrist strap or anti-static gloves when handling the devices. All equipment, including workstations and soldering irons, must be properly grounded.

8. Packaging and Ordering Information

8.1 Tape and Reel Specifications

The LTST-C190KEKT is supplied standard on 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels. This packaging is compliant with ANSI/EIA-481 specifications for automated handling.

• Quantity per Reel: 4000 pieces.
• Minimum Order Quantity (MOQ) for Remainders: 500 pieces.
• Pocket Coverage: Empty component pockets on the tape are sealed with a top cover tape.
• Missing Components: The maximum allowable number of consecutive missing lamps on a reel is two.

Detailed dimensional drawings for the tape pocket and the reel are provided in the datasheet for machine setup and compatibility verification.

9. Technical Comparison and Differentiation

The LTST-C190KEKT utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material. Compared to older technologies like standard GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in brighter output for the same drive current. It also typically provides better temperature stability of both light output and wavelength. The wide 130-degree viewing angle is a design choice that differentiates it from LEDs with narrower beams, making it ideal for area illumination and status indicators that need to be visible from a wide range of angles.

10. Frequently Asked Questions (Based on Technical Parameters)

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

Peak Wavelength (λ_P): The specific wavelength where the LED emits the most optical power. It's a physical measurement from the spectrum.
Dominant Wavelength (λ_d): A calculated value from the CIE color chart that corresponds to the perceived color of the light by the human eye. For a monochromatic source like a red LED, they are often close, but λ_d is the parameter used for color specification and binning.

10.2 Why is a current-limiting resistor necessary even if I power the LED at its typical forward voltage?

The forward voltage (V_F) has a tolerance range (1.7V to 2.5V). If you apply a constant 2.0V, an LED with a low V_F of 1.7V might draw excessive current, while one with a high V_F of 2.5V might not light at all. More critically, V_F decreases with increasing temperature. A constant voltage source can lead to thermal runaway: as the LED heats up, V_F drops, current increases, causing more heat, further dropping V_F, until failure. A series resistor (or, better, a constant current driver) provides negative feedback, stabilizing the operating point.

10.3 Can I drive this LED with a 3.3V or 5V logic signal directly?

No. Connecting it directly to a 3.3V or 5V digital output pin would apply that voltage across the LED. With a typical V_F of ~2.0V, the excess voltage would cause a very high current to flow, limited only by the small internal resistance of the chip and the output pin, likely destroying the LED instantly. You must always use a series current-limiting resistor when driving an LED from a voltage source.

11. Practical Application Example

Scenario: Designing a multi-LED status indicator panel for a network router.
The panel requires 5 red status LEDs to indicate power, internet connection, Wi-Fi activity, etc. The system uses a 3.3V supply rail.
Design Steps:
1. Choose Operating Current: Select I_F = 20mA, which is the standard test condition and provides good brightness within the safe operating area.
2. Calculate Resistor Value: Use the maximum V_F from the datasheet (2.5V) for a conservative design ensuring all LEDs light even with high-V_F parts. R = (3.3V - 2.5V) / 0.020A = 40 Ohms. The nearest standard value is 39 Ohms or 43 Ohms.
3. Check Power in Resistor: P_R = I_F² * R = (0.02)² * 39 = 0.0156W. A standard 1/10W (0.1W) resistor is more than sufficient.
4. Circuit Layout: Implement five identical circuits, each with one LED and one 39-ohm resistor in series, all connected between the 3.3V rail and individual microcontroller GPIO pins set as outputs. Driving a pin LOW (0V) will complete the circuit and turn the LED on.
5. PCB Design: Use the recommended land pattern from the datasheet. Ensure adequate trace width for the 20mA current.

12. Operating Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through a process called electroluminescence. When a forward voltage is applied across the p-n junction of the semiconductor material (in this case, AlInGaP), electrons from the n-type region and holes from the p-type region are injected into the junction region. When an electron recombines with a hole, it falls from a higher energy state in the conduction band to a lower energy state in the valence band. The energy difference is released in the form of a photon (light particle). The wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material, which is a fundamental property of the AlInGaP compound used here, resulting in red light emission.

13. Technology Trends

The optoelectronics industry continues to evolve with several key trends impacting SMD LEDs like the LTST-C190KEKT. There is a constant drive for increased luminous efficacy (more light output per electrical watt input), which improves energy efficiency. Miniaturization remains critical, pushing for smaller package sizes while maintaining or improving optical performance. Enhanced reliability and longer operational lifetimes under various environmental conditions are also major development goals. Furthermore, tighter binning tolerances for color and brightness are becoming standard to meet the demands of high-quality display and lighting applications where color consistency is paramount.