Dual Color SMD LED LTST-C295TBKGKT-5A Datasheet - Size 2.0x1.25x0.55mm - Voltage 2.7V/1.75V - Power 0.076W/0.075W - Blue/Green

1. Product Overview

This document details the specifications for a dual-color, surface-mount device (SMD) LED. The component integrates two distinct LED chips within a single, ultra-thin package, enabling the emission of blue and green light from a single footprint. It is designed for modern electronic assembly processes, featuring compatibility with automatic placement equipment and infrared (IR) reflow soldering profiles suitable for lead-free processes. The product adheres to environmental standards as a ROHS-compliant green product.

1.1 Core Advantages

• Space-Saving Design: An extra-thin profile of 0.55mm allows for integration into compact and low-profile electronic devices.
• Dual-Color Functionality: Combines blue (InGaN) and green (AlInGaP) light sources, offering design flexibility for status indicators, backlighting, and decorative lighting.
• High-Brightness Output: Utilizes advanced InGaN and AlInGaP semiconductor materials to deliver high luminous intensity.
• Manufacturing Friendly: Packaged in 8mm tape on 7-inch reels, conforming to EIA standards, making it ideal for high-volume, automated PCB assembly lines.
• Process Compatibility: Withstands standard IR reflow soldering conditions, ensuring reliability in standard SMT manufacturing workflows.

2. In-Depth Technical Parameter Analysis

The following section provides a detailed breakdown of the electrical, optical, and thermal characteristics of the device. All parameters are specified at an ambient temperature (Ta) of 25°C unless otherwise noted.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under or at these conditions is not guaranteed.

Parameter	Blue Chip	Green Chip	Unit	Condition
Power Dissipation	76	75	mW	-
Peak Forward Current	100	80	mA	1/10 Duty Cycle, 0.1ms Pulse
DC Forward Current	20	30	mA	Continuous
Operating Temperature	-20°C to +80°C		-	-
Storage Temperature	-30°C to +100°C		-	-
IR Soldering Condition	260°C for 10 seconds		-	Peak temperature

Interpretation: The green chip can handle a higher continuous DC current (30mA vs. 20mA), while the blue chip has a higher permissible pulsed current. The specified IR reflow profile is critical for ensuring solder joint integrity without damaging the LED package.

2.2 Electrical & Optical Characteristics

These are the typical operating parameters that define the device's performance under standard test conditions (IF = 5 mA).

Parameter	Symbol	Blue Chip (Min/Typ/Max)	Green Chip (Min/Typ/Max)	Unit	Test Condition
Luminous Intensity	Iv	7.10 / - / 45.0	7.10 / - / 45.0	mcd	IF = 5 mA
Viewing Angle	2θ1/2	130 (Typical)		deg	-
Peak Wavelength	λP	468 (Typical)	574 (Typical)	nm	-
Dominant Wavelength	λd	- / 470 / -	- / 571 / -	nm	IF = 5 mA
Spectral Half-Width	Δλ	25 (Typical)	15 (Typical)	nm	-
Forward Voltage	VF	- / 2.70 / 3.20	- / 1.75 / 2.35	V	IF = 5 mA
Reverse Current	IR	10 (Max)	10 (Max)	μA	VR = 5V

Key Analysis:

• Brightness & Binning: The luminous intensity has a wide range (7.1 to 45 mcd), which is managed through a binning system (detailed in Section 3). Designers must account for this variation in their optical design.
• Voltage Difference: The forward voltage (V_F) is significantly different between the blue (~2.7V) and green (~1.75V) chips. This is a critical consideration for circuit design, especially when driving both colors from a common current source or voltage rail. Separate current-limiting resistors are typically required for each color channel.
• Viewing Angle: A wide 130-degree viewing angle makes this LED suitable for applications requiring broad visibility.
• ESD Sensitivity: The note on ESD caution indicates the device is sensitive to electrostatic discharge. Proper ESD handling procedures (wrist straps, grounded equipment) are mandatory during assembly and handling.
• Non-Rectifying Operation: The reverse current test note explicitly states the device is not designed for reverse operation. Applying a reverse bias beyond the test condition can cause immediate failure.

3. Binning System Explanation

To ensure consistency in brightness, the LEDs are sorted into bins based on their measured luminous intensity at 5 mA. This allows designers to select a brightness grade suitable for their application.

3.1 Luminous Intensity Binning

The binning structure is identical for both the blue and green chips.

Bin Code	Minimum Intensity (mcd)	Maximum Intensity (mcd)
K	7.10	11.2
L	11.2	18.0
M	18.0	28.0
N	28.0	45.0

Tolerance: Each intensity bin has a +/-15% tolerance. For example, an LED from bin "M" could have an actual intensity between 15.3 mcd and 32.2 mcd at the test current.

Design Implication: When precise brightness matching is required (e.g., in multi-LED arrays or color mixing), specifying a tighter bin code or implementing calibration in the driving circuit may be necessary.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet (pages 6-7), typical performance trends can be inferred from the parameters:

• I-V (Current-Voltage) Curve: The forward voltage (V_F) will increase with forward current (I_F). The relationship is non-linear and characteristic of a diode. The different V_F values for blue and green chips mean their I-V curves will be offset from each other.
• Luminous Intensity vs. Current: Light output (Iv) generally increases with forward current but will eventually saturate. Operating above the absolute maximum DC current will reduce efficiency and lifespan.
• Temperature Dependence: Luminous intensity typically decreases as junction temperature increases. The operating temperature range of -20°C to +80°C defines the ambient conditions over which the specified optical performance is maintained. Forward voltage also has a negative temperature coefficient (decreases with temperature).
• Spectral Distribution: The peak wavelengths (468nm blue, 574nm green) and spectral half-widths (25nm blue, 15nm green) define the color purity. The green chip, with a narrower half-width, emits a more spectrally pure green light compared to the broader blue emission.

5. Mechanical & Package Information

5.1 Package Dimensions

The device features an industry-standard SMD package. Key dimensions include a body size of approximately 2.0mm x 1.25mm with a height of only 0.55mm. Detailed dimensional drawings with tolerances of ±0.10mm are provided in the datasheet for accurate PCB footprint design.

5.2 Pin Assignment & Polarity

The dual-color LED has four pins (1, 2, 3, 4). The pin assignment is as follows:

• Blue Chip: Connected to pins 1 and 3.
• Green Chip: Connected to pins 2 and 4.

This configuration typically implies a common-cathode or common-anode structure internally, but the datasheet specifies the pin pairs for each color. The polarity must be observed when connecting to the driving circuit. The package is marked for orientation (likely with a dot or chamfer on pin 1).

5.3 Recommended Solder Pad Design

A suggested solder pad layout is included to ensure reliable soldering and proper mechanical alignment during reflow. Following these recommendations helps prevent tombstoning (component standing up on one end) and ensures good solder fillets.

6. Soldering & Assembly Guidelines

6.1 IR Reflow Soldering Profile

A detailed suggested reflow profile is provided for lead-free (Pb-free) solder processes. Key parameters include:

• Preheat: 150-200°C for a maximum of 120 seconds to gradually heat the board and activate flux.
• Peak Temperature: Maximum of 260°C.
• Time Above Liquidus: The component should be exposed to the peak temperature for a maximum of 10 seconds.
• Limit: The device should not undergo more than two reflow cycles under these conditions.

This profile is based on JEDEC standards to ensure package integrity. The low thermal mass of the LED requires careful profile tuning to avoid overheating.

6.2 Hand Soldering

If hand soldering is necessary, it should be performed with extreme care:

• Iron Temperature: Maximum 300°C.
• Soldering Time: Maximum 3 seconds per solder joint.
• Limit: Only one hand-soldering cycle is permitted.

Excessive heat or prolonged contact can damage the LED chip or the plastic lens.

6.3 Cleaning

If post-solder cleaning is required:

• Use only specified solvents: ethyl alcohol or isopropyl alcohol.
• Immersion time should be less than one minute at normal room temperature.
• Avoid aggressive or unspecified chemical cleaners, as they can damage the LED package material and optical lens.

6.4 Storage Conditions

Proper storage is essential to prevent moisture absorption, which can cause "popcorning" (package cracking) during reflow.

• Sealed Package: Store at ≤30°C and ≤90% RH. Use within one year of opening the moisture barrier bag.
• Opened Package: Store at ≤30°C and ≤60% RH. Use within one week. For longer storage, place in a sealed container with desiccant or in a nitrogen desiccator.
• Rebaking: Components stored out of their original packaging for more than one week should be baked at approximately 60°C for at least 20 hours before soldering to remove absorbed moisture.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The device is supplied in a format optimized for automated pick-and-place machines:

• Tape Width: 8mm.
• Reel Size: 7 inches in diameter.
• Quantity per Reel: 4000 pieces.
• Minimum Order Quantity: 500 pieces for remainder quantities.
• Packaging Standard: Complies with ANSI/EIA-481 specifications. Empty pockets are sealed with cover tape.

8. Application Suggestions

8.1 Typical Application Scenarios

• Status Indicators: Dual-color capability allows for multiple status signals (e.g., power on=green, standby=blue, fault=alternating).
• Backlighting: For small LCD displays, keypads, or panel indicators where space is limited.
• Decorative Lighting: In consumer electronics, toys, or appliances where colored lighting effects are desired.
• Automotive Interior Lighting: For non-critical interior illumination, given the operating temperature range.
• IoT Devices & Wearables: The thin profile and low power consumption make it suitable for compact, portable electronics.

8.2 Critical Design Considerations

• Current Limiting: ALWAYS use external current-limiting resistors in series with each LED chip. Calculate resistor values based on the supply voltage, the desired forward current (not exceeding the DC rating), and the typical V_F for each color. Do not connect directly to a voltage source.
• Thermal Management: Although power dissipation is low, ensure adequate PCB copper area or thermal relief, especially if operating near maximum current or in high ambient temperatures, to prevent overheating and premature brightness degradation.
• ESD Protection: Implement ESD protection diodes on PCB lines connected to the LED pins if the assembly environment or end-use scenario poses an ESD risk.
• Optical Design: Account for the wide viewing angle and potential brightness variation (binning) in the design of light guides, diffusers, or lenses.

9. Technical Comparison & Differentiation

Compared to single-color LEDs or older dual-color packages, this device offers distinct advantages:

• vs. Two Discrete LEDs: Saves significant PCB space (one footprint vs. two), reduces placement time, and simplifies bill of materials.
• vs. Thicker Dual-Color LEDs: The 0.55mm height enables use in ultra-thin devices like modern smartphones, tablets, and slim laptops where z-height is a critical constraint.
• vs. Non-Reflow Compatible LEDs: Direct compatibility with standard SMT reflow processes eliminates the need for secondary manual soldering steps, improving manufacturing yield and reliability.
• Chip Technology: The use of InGaN for blue and AlInGaP for green represents advanced semiconductor materials known for high efficiency and brightness compared to older technologies.

10. Frequently Asked Questions (FAQs)

10.1 Can I drive both the blue and green LEDs simultaneously at their maximum DC current?

No. The Absolute Maximum Ratings specify power dissipation limits per chip (76mW for blue, 75mW for green). Simultaneously driving both at their max DC current (20mA for blue, 30mA for green) and typical V_F would result in power levels of approximately 54mW and 52.5mW respectively, which are within limits. However, the total heat generated in the tiny package must be considered. For reliable long-term operation, it is advisable to drive them at currents lower than the maximum, especially if both are on continuously.

10.2 Why are the forward voltages so different?

The forward voltage is a fundamental property of the semiconductor material's bandgap. Blue light, with its higher photon energy (shorter wavelength), requires a semiconductor with a wider bandgap (InGaN), which inherently has a higher forward voltage. Green light (AlInGaP) has a slightly lower photon energy, corresponding to a lower bandgap and thus a lower forward voltage. This is a physical characteristic, not a defect.

10.3 How do I interpret the bin code when ordering?

The bin code (e.g., "K", "L", "M", "N") defines the guaranteed minimum brightness of the LED. If your design requires a minimum brightness of 18 mcd, you should specify bin code "M" or higher ("N"). If brightness is not critical, a lower bin code ("K" or "L") may be more cost-effective. Consult with the supplier for available bin codes.

10.4 Is this LED suitable for outdoor use?

The operating temperature range (-20°C to +80°C) covers many outdoor conditions. However, the datasheet does not specify an Ingress Protection (IP) rating against dust and water. For outdoor use, the LED would need to be properly encapsulated or housed within a sealed assembly to protect it from direct environmental exposure, moisture, and UV radiation, which can degrade the plastic lens over time.

11. Practical Design Case Study

Scenario: Designing a compact IoT sensor node with a dual-color status LED. The device is powered by a 3.3V regulator and uses a microcontroller with GPIO pins capable of sourcing 20mA.

Implementation:

1. Circuit Design: Two GPIO pins are used. Each pin connects to a current-limiting resistor, then to one color of the LED (Pin1-3 for blue, Pin2-4 for green). The common connection (e.g., cathodes) is tied to ground.
2. Resistor Calculation (Example for 10mA drive):
   • Blue: R_Blue = (3.3V - 2.7V) / 0.01A = 60Ω. Use a standard 62Ω or 68Ω resistor.
   • Green: R_Green = (3.3V - 1.75V) / 0.01A = 155Ω. Use a standard 150Ω resistor.
   This ensures both colors have similar perceived brightness at the same current, though final values may need adjustment based on actual V_F and desired intensity.
3. PCB Layout: The footprint follows the recommended solder pad design. Small thermal relief connections are used on the pads to facilitate soldering while providing some thermal conduction to the PCB ground plane for heat dissipation.
4. Software: The microcontroller firmware can control the LEDs for various states: Solid Green (operational), Flashing Blue (data transmission), Alternating (error), etc.

This case highlights the importance of separate current-limiting calculations and the utility of a single component for multiple visual feedback states.

12. Operating Principle

Light emission in LEDs is based on electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the material's bandgap is applied, electrons and holes are injected across the junction. When these charge carriers recombine, they release energy in the form of photons (light). The color (wavelength) of the emitted light is directly determined by the energy bandgap of the semiconductor material. The InGaN chip has a wider bandgap, emitting higher-energy blue photons, while the AlInGaP chip has a narrower bandgap, emitting lower-energy green photons. The two chips are housed in a single package with a water-clear lens that minimally alters the emitted light, providing a compact dual-light source solution.

13. Technology Trends

The development of LEDs like this one is part of broader trends in optoelectronics:

• Miniaturization: Continuous reduction in package size (footprint and height) to enable ever-smaller and thinner end products.
• Increased Integration: Moving beyond dual-color to RGB (Red, Green, Blue) packages and even packages with integrated drivers or control ICs ("smart LEDs").
• Higher Efficiency: Ongoing improvements in internal quantum efficiency (IQE) and light extraction techniques yield brighter LEDs at lower drive currents, reducing overall system power consumption.
• Improved Reliability: Advancements in packaging materials (epoxies, silicones) and chip design enhance longevity and resistance to thermal stress and environmental factors.
• Expanded Color Gamut: Development of new semiconductor materials and phosphors to produce purer and more saturated colors, as well as precise white color temperatures, for advanced display and lighting applications.

Devices such as the one described here represent a mature, cost-effective solution for standard indicator and functional lighting needs, benefiting from these ongoing industry advancements.