Dual Color SMD LED LTST-C235TBKFWT Datasheet - Package Dimensions - Blue/Orange - 3.3V/2.0V - 76mW/75mW - English Technical Document

1. Product Overview

The LTST-C235TBKFWT is a dual-color, surface-mount device (SMD) LED designed for modern electronic applications requiring compact, reliable, and bright indicator solutions. It integrates two distinct semiconductor chips within a single EIA-standard package: an InGaN (Indium Gallium Nitride) chip for blue emission and an AlInGaP (Aluminum Indium Gallium Phosphide) chip for orange emission. This configuration allows for versatile signaling and status indication using a single component footprint.

The product is classified as a green product, meeting ROHS (Restriction of Hazardous Substances) compliance standards, making it suitable for use in markets with strict environmental regulations. It is packaged in 8mm tape on 7-inch diameter reels, facilitating high-speed automated pick-and-place assembly processes common in volume electronics manufacturing.

1.1 Core Features and Advantages

• Dual Color Source: Combines blue (InGaN) and orange (AlInGaP) light emission from separate chips.
• High Brightness: Utilizes ultra-bright chip technology for strong luminous intensity.
• Manufacturing Compatibility: Fully compatible with automatic placement equipment and standard infrared (IR) reflow soldering processes.
• IC Compatibility: Can be driven directly by most logic-level outputs.
• Standardized Packaging: EIA standard package ensures broad compatibility with industry designs and assembly lines.

2. Technical Parameter Analysis

This section provides a detailed, objective interpretation of the key electrical and optical parameters specified for the LTST-C235TBKFWT LED. All values are 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. Operation under these conditions is not guaranteed.

• Power Dissipation (Pd): Blue: 76 mW, Orange: 75 mW. This is the maximum power the LED can dissipate as heat under DC operation.
• Peak Forward Current (I_FP): Blue: 100 mA, Orange: 80 mA. This is the maximum allowable instantaneous current under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). Exceeding this can cause catastrophic failure.
• DC Forward Current (I_F): Blue: 20 mA, Orange: 30 mA. This is the recommended maximum continuous forward current for reliable long-term operation.
• Temperature Ranges: Operating: -20°C to +80°C; Storage: -30°C to +100°C.
• Soldering Condition: Withstands infrared reflow soldering at a peak temperature of 260°C for 10 seconds.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters under specified test conditions.

• Luminous Intensity (I_V): Measured in millicandelas (mcd) at I_F = 20 mA. Blue: Min. 18.0, Typ. 45.0, Max. 280.0. Orange: Min. 28.0, Typ. value not stated, Max. not applicable from table. This indicates the perceived brightness of the LED to the human eye.
• Viewing Angle (2θ_1/2): Typically 130 degrees for both colors. This is the full angle at which the luminous intensity drops to half of its on-axis value, defining the beam spread.
• Peak Wavelength (λ_P): Blue: 468 nm (Typ.), Orange: 611 nm (Typ.). This is the wavelength at which the spectral output is strongest.
• Dominant Wavelength (λ_d): Blue: 470 nm (Typ.), Orange: 605 nm (Typ.). This is the single wavelength that best represents the perceived color of the LED, derived from the CIE chromaticity diagram.
• Spectral Line Half-Width (Δλ): Blue: 25 nm (Typ.), Orange: 17 nm (Typ.). This measures the spectral purity or bandwidth of the emitted light.
• Forward Voltage (V_F): At I_F = 20 mA. Blue: Typ. 3.30V, Max. 3.80V. Orange: Typ. 2.00V, Max. 2.40V. This is the voltage drop across the LED when operating.
• Reverse Current (I_R): Max. 10 μA for both at V_R = 5V. The device is not designed for reverse bias operation; this parameter is for leakage characterization only.

3. Binning System Explanation

The luminous intensity of LEDs can vary from batch to batch. A binning system is used to sort LEDs into groups (bins) based on their measured performance, ensuring consistency for the end-user.

3.1 Luminous Intensity Binning

The LTST-C235TBKFWT uses letter codes to denote intensity ranges. The tolerance within each bin is +/-15%.

Blue Chip Bins:
- M: 18.0 - 28.0 mcd
- N: 28.0 - 45.0 mcd
- P: 45.0 - 71.0 mcd
- Q: 71.0 - 112.0 mcd
- R: 112.0 - 180.0 mcd

Orange Chip Bins:
- N: 28.0 - 45.0 mcd
- P: 45.0 - 71.0 mcd
- Q: 71.0 - 112.0 mcd
- R: 112.0 - 180.0 mcd
- S: 180.0 - 280.0 mcd

This system allows designers to select a brightness grade suitable for their application's requirements, whether for high-ambient-light visibility or lower-power indication.

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet (e.g., Fig.1, Fig.5), typical performance curves for such LEDs provide critical design insights.

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

The I-V relationship is exponential. For the blue chip (InGaN, V_F ~3.3V), the curve will have a steeper knee compared to the orange chip (AlInGaP, V_F ~2.0V). This necessitates different current-limiting resistor values when driving from the same voltage source to achieve the same target current (e.g., 20mA).

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to forward current within the recommended operating range. However, efficiency (light output per unit of electrical input) typically decreases at very high currents due to increased heat generation. Operating at or below the recommended DC forward current ensures optimal efficiency and longevity.

4.3 Temperature Dependence

LED performance is temperature-sensitive. As junction temperature increases:
- Luminous intensity generally decreases.
- Forward voltage typically decreases slightly for a given current.
- The dominant wavelength may shift (usually towards longer wavelengths).
Proper thermal management in the PCB design is crucial for maintaining consistent optical performance over the operating temperature range.

5. Mechanical & Package Information

5.1 Package Dimensions and Pin Assignment

The device conforms to an EIA standard SMD LED footprint. The specific dimensions are provided in the datasheet drawings. The pin assignment is critical for correct operation:
- Pins 1 and 2: Anode and Cathode for the Blue InGaN chip.
- Pins 3 and 4: Anode and Cathode for the Orange AlInGaP chip.
Consulting the package drawing is essential to identify the anode/cathode polarity for each color to avoid incorrect connection during PCB layout.

5.2 Recommended Solder Pad Design

The datasheet includes suggested solder pad dimensions. Following these recommendations ensures a reliable solder joint, proper alignment during reflow, and aids in heat dissipation from the LED package. Deviating significantly from these pad layouts can lead to tombstoning (component standing up), poor solder fillets, or reduced thermal performance.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profile

The datasheet provides a suggested IR reflow profile for lead-free (Pb-free) solder processes. Key parameters include:
- Pre-heat: 150-200°C to gradually heat the board and activate flux.
- Pre-heat Time: Maximum 120 seconds to prevent thermal shock.
- Peak Temperature: Maximum 260°C.
- Time Above Liquidus: The profile on page 3 shows the critical reflow zone; the component should be exposed to temperatures sufficient for solder melting (typically 217°C+ for SnAgCu) for an appropriate time (e.g., 60-90 seconds).
- Cooling Rate: Controlled cooling is recommended to minimize stress on solder joints.

6.2 Hand Soldering

If hand soldering is necessary:
- Use a temperature-controlled soldering iron set to a maximum of 300°C.
- Limit soldering time to a maximum of 3 seconds per joint.
- Apply heat to the PCB pad, not directly to the LED body, to prevent thermal damage to the plastic lens and semiconductor die.

6.3 Cleaning

If post-solder cleaning is required:
- Use only specified cleaning agents. Unspecified chemicals may damage the LED's epoxy lens, causing clouding or cracking.
- Recommended solvents are ethyl alcohol or isopropyl alcohol at normal room temperature.
- Immersion time should be less than one minute to prevent solvent ingress.

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: As a surface-mount plastic package, it is moisture-sensitive. If the original sealed moisture-barrier bag is opened, the components should be used within one week or baked (e.g., at 60°C for 20 hours) before reflow to remove absorbed moisture and prevent \"popcorning\" damage during soldering.
• Long-term Storage: For opened packages, store at ≤30°C and ≤60% relative humidity. For extended storage, use a sealed container with desiccant.

7. Packaging and Ordering

7.1 Tape and Reel Specifications

The standard packaging is 8mm embossed carrier tape on 7-inch (178mm) diameter reels.
- Quantity per Reel: 3000 pieces.
- Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
- Cover Tape: Empty pockets are sealed with top cover tape.
- Missing Components: A maximum of two consecutive missing LEDs is allowed per the packaging standard (ANSI/EIA 481-1-A-1994).

8. Application Recommendations

8.1 Typical Application Scenarios

• Status Indicators: Dual-color capability allows for multiple statuses (e.g., blue for \"on/standby,\" orange for \"fault/charging,\" both for a third state).
• Consumer Electronics: Power buttons, connectivity status (Wi-Fi/Bluetooth), battery level indicators on laptops, routers, and peripherals.
• Industrial Control Panels: Machine status, operational mode indication.
• Automotive Interior Lighting: Low-power accent or indicator lighting, though specific automotive-grade qualification would be required.

8.2 Design Considerations

• Current Limiting: Always use a series resistor for each LED chip to set the forward current. Calculate resistor value as R = (V_source - V_F) / I_F. Use the maximum V_F from the datasheet for a conservative design that ensures I_F is not exceeded even with component variation.
• Driving Circuit: The LEDs are compatible with microcontroller GPIO pins. Ensure the GPIO can sink/source the required current (20-30mA). For higher currents or multiplexing many LEDs, use transistor drivers or dedicated LED driver ICs.
• Thermal Management: While power dissipation is low, ensure the PCB layout provides adequate copper area around the solder pads to act as a heat sink, especially if operating at high ambient temperatures or maximum current.
• Optical Design: The 130-degree viewing angle provides a wide, diffuse light pattern suitable for direct viewing. For light-piping applications, the wide angle helps couple light into the pipe effectively.

9. Technical Comparison and Differentiation

The LTST-C235TBKFWT offers specific advantages in its class:

• Dual-Chip vs. Single-Chip: Compared to using two separate single-color LEDs, this device saves PCB space, reduces component count, and simplifies assembly.
• Chip Technology: The use of InGaN for blue and AlInGaP for orange represents mature, high-efficiency semiconductor technologies for their respective colors, offering good brightness and reliability.
• Package Standardization: The EIA-standard package ensures drop-in compatibility with a vast array of existing PCB footprints and design libraries, reducing design risk.
• Process Compatibility: Full compatibility with IR reflow and automated placement makes it ideal for high-volume, cost-sensitive manufacturing.

10. Frequently Asked Questions (FAQs)

Q1: Can I drive both the blue and orange LEDs simultaneously at their maximum DC current?
A1: Yes, but you must consider the total power dissipation. Simultaneous operation at 20mA (Blue) and 30mA (Orange) results in a power dissipation of approximately (3.3V*0.02A) + (2.0V*0.03A) = 0.126W. This is below the individual maximums but requires checking that the combined thermal load does not exceed the package's ability to dissipate heat in your specific layout.

Q2: What is the difference between peak wavelength and dominant wavelength?
A2: Peak wavelength (λ_P) is the physical wavelength of the highest intensity point in the emission spectrum. Dominant wavelength (λ_d) is a calculated value based on human color perception (CIE chart) that defines the \"color\" we see. For monochromatic LEDs, they are often close. For LEDs with broader spectra, they can differ.

Q3: How do I interpret the bin code when ordering?
A3: The bin code (e.g., \"P\" for blue, \"Q\" for orange) specifies the guaranteed minimum and maximum luminous intensity range for that batch. You must specify the desired bin(s) when ordering to ensure brightness consistency across your production run. If not specified, you may receive components from any available bin within the product's overall range.

Q4: Is this LED suitable for outdoor use?
A4: The operating temperature range (-20°C to +80°C) covers many outdoor conditions. However, long-term outdoor exposure requires consideration of additional factors not covered in this datasheet: UV resistance of the lens (to prevent yellowing), resistance to thermal cycling, and protection against moisture ingress. For critical outdoor applications, consult the manufacturer for extended reliability data or consider products specifically qualified for outdoor use.

11. Design and Usage Case Study

Scenario: Designing a Dual-Status Power Button for a Network Switch
A designer needs an LED to indicate both power state (On/Off) and network activity (Active/Idle) on a single button.

Implementation:
1. The LTST-C235TBKFWT is placed behind a translucent button cap.
2. The microcontroller drives the LEDs:
- Solid Orange: Power is ON, device is booting/idle.
- Solid Blue: Power is ON, device is fully operational and idle.
- Blinking Blue: Power is ON, network activity is detected.
- Off: Power is OFF.
3. Current-limiting resistors are calculated separately for each color. For a 3.3V MCU rail: R_Blue = (3.3V - 3.3V) / 0.02A = 0Ω (theoretical). In practice, a small resistor (e.g., 10Ω) is used to limit inrush current and account for MCU pin voltage drop. R_Orange = (3.3V - 2.0V) / 0.02A = 65Ω (a 68Ω standard value is used).
4. The wide 130-degree viewing angle ensures the button is evenly illuminated from various viewing angles.

Outcome: A clean, compact user interface with clear, multi-state feedback using only one component footprint, simplifying PCB layout and assembly.

12. Technology Principle Introduction

Light Emission Principle: LEDs are semiconductor diodes. When a forward voltage is applied, electrons cross the p-n junction and recombine with holes in the active region. This recombination releases energy in the form of photons (light). The specific wavelength (color) of the light is determined by the bandgap energy of the semiconductor material used.

Material Science:
- InGaN (Indium Gallium Nitride): This material system allows for the tuning of the bandgap to produce light from ultraviolet through green and blue. The blue chip in this LED uses this technology.
- AlInGaP (Aluminum Indium Gallium Phosphide): This material system is used for high-brightness LEDs in the yellow, orange, and red spectrum. The orange chip in this LED uses this technology.

The combination of these two mature material technologies in one package provides a reliable solution for dual-color applications.

13. Industry Trends and Developments

The field of SMD LEDs continues to evolve. General trends relevant to components like the LTST-C235TBKFWT include:

• Increased Efficiency (lm/W): Ongoing improvements in epitaxial growth and chip design lead to higher luminous efficacy, meaning more light output for the same electrical input power.
• Miniaturization: While this product uses a standard package, the industry pushes for smaller footprints (e.g., 0402, 0201) for space-constrained applications like mobile devices.
• Improved Color Consistency: Tighter binning tolerances and advances in manufacturing control yield LEDs with more consistent chromaticity and brightness from batch to batch.
• Higher Reliability and Lifetime: Enhancements in packaging materials (epoxy, lead frames) and chip structures aim to extend operational lifetime and improve performance under high-temperature and high-humidity conditions.
• Integration: Beyond dual-color, there is a trend towards integrating more functions, such as RGB (Red, Green, Blue) LEDs in a single package, or even combining LEDs with control ICs (like driver or sequencer chips) into more complex modules.

The LTST-C235TBKFWT represents a well-established, reliable solution within this evolving landscape, offering a balance of performance, cost, and manufacturability for mainstream dual-color indicator applications.