LTST-C195TGKSKT Dual Color SMD LED Datasheet - EIA Package - Green/Yellow - 20mA/30mA - English Technical Document

1. Product Overview

The LTST-C195TGKSKT is a dual-color, surface-mount LED designed for modern electronic applications requiring compact size and reliable performance. It integrates two distinct semiconductor chips within a single EIA standard package: an InGaN (Indium Gallium Nitride) chip for green emission and an AlInGaP (Aluminum Indium Gallium Phosphide) chip for yellow emission. This configuration allows for bi-color indication or simple color mixing in a minimal footprint. The device is supplied on 8mm tape wound onto 7-inch reels, making it fully compatible with high-speed automated pick-and-place assembly equipment. Its design adheres to RoHS directives, ensuring it is free from hazardous substances like lead, mercury, and cadmium.

1.1 Core Advantages

• Dual Color Source: Combines green and yellow light emission in one package, saving board space and simplifying design for multi-status indication.
• High Brightness: Utilizes advanced InGaN and AlInGaP chip technology to deliver high luminous intensity.
• Robust Packaging: The EIA standard package ensures mechanical compatibility and reliable soldering.
• Process Compatibility: Suitable for standard infrared (IR) reflow, vapor phase reflow, and wave soldering processes, including lead-free (Pb-free) assembly profiles.
• Automation Ready: Packaged on tape and reel for efficient, high-volume manufacturing.

2. In-Depth Technical Parameter Analysis

All parameters are specified at an ambient temperature (Ta) of 25°C unless otherwise noted. Understanding these specifications is critical for reliable circuit design and achieving desired performance.

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): Green: 76 mW, Yellow: 75 mW. This is the maximum power the LED can dissipate as heat.
• Peak Forward Current (I_FP): Green: 100 mA, Yellow: 80 mA. Applicable only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width).
• DC Forward Current (I_F): Green: 20 mA, Yellow: 30 mA. The recommended continuous operating current.
• Derating: Green: 0.25 mA/°C, Yellow: 0.4 mA/°C. The maximum forward current must be reduced linearly above 25°C ambient temperature according to this factor.
• Reverse Voltage (V_R): 5 V for both colors. Exceeding this voltage in reverse bias can cause junction breakdown.
• Temperature Range: Operating: -20°C to +80°C; Storage: -30°C to +100°C.
• Soldering Temperature: Withstands 260°C for 5 seconds (IR/Wave) or 215°C for 3 minutes (Vapor Phase).

2.2 Electrical & Optical Characteristics

These are the typical performance parameters under normal operating conditions (I_F = 20mA).

• Luminous Intensity (I_V): A key measure of brightness.
  • Green: Typical 180 mcd (Min. 45 mcd, see Bin Code).
  • Yellow: Typical 75 mcd (Min. 28 mcd, see Bin Code).
  • Measured using a sensor filtered to match the human eye's photopic response (CIE curve).
• Viewing Angle (2θ_1/2): 130 degrees (typical) for both colors. This is the full angle at which intensity drops to half its on-axis value, indicating a wide viewing pattern.
• Peak Wavelength (λ_P): Green: 525 nm (typical), Yellow: 591 nm (typical). The wavelength at which the emitted optical power is maximum.
• Dominant Wavelength (λ_d): Green: 530 nm (typical), Yellow: 589 nm (typical). The single wavelength perceived by the human eye, defining the color point on the CIE chromaticity diagram.
• Spectral Bandwidth (Δλ): Green: 35 nm (typical), Yellow: 15 nm (typical). The width of the emission spectrum at half its maximum power (FWHM). Yellow AlInGaP LEDs typically have a narrower spectrum than green InGaN LEDs.
• Forward Voltage (V_F):
  • Green: Typical 3.30 V, Maximum 3.50 V @ 20mA. The higher voltage is characteristic of InGaN-based blue/green/white LEDs.
  • Yellow: Typical 2.00 V, Maximum 2.40 V @ 20mA. The lower voltage is characteristic of AlInGaP-based red/yellow/orange LEDs.
• Reverse Current (I_R): Maximum 10 µA @ V_R=5V for both colors.
• Capacitance (C): Typical 40 pF @ V_F=0V, f=1MHz for the yellow chip. Not specified for green.

3. Binning System Explanation

To ensure consistency in brightness, LEDs are sorted into performance bins. The LTST-C195TGKSKT uses a luminous intensity binning system.

3.1 Luminous Intensity Bins

Intensity is measured at the standard test current of 20mA. Each bin has a tolerance of ±15%.

Green Color Bins:

• Bin P: 45.0 mcd (Min) to 71.0 mcd (Max)
• Bin Q: 71.0 mcd to 112.0 mcd
• Bin R: 112.0 mcd to 180.0 mcd
• Bin S: 180.0 mcd to 280.0 mcd

Yellow Color Bins:

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

Designers should specify the required bin code when ordering to guarantee brightness uniformity across multiple units in an application.

4. Performance Curve Analysis

While specific graphs are referenced in the datasheet (Fig.1, Fig.6), the following trends are standard for such LEDs and can be inferred from the provided data:

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

The I-V relationship is exponential. The specified V_F at 20mA provides one operating point. The green LED's higher V_F requires a higher drive voltage compared to the yellow LED for the same current. A current-limiting resistor is essential to set the operating point correctly and prevent thermal runaway.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to forward current in the normal operating range (up to I_F). Operating above the recommended DC current will increase brightness but also power dissipation and junction temperature, potentially reducing lifespan and shifting color.

4.3 Temperature Dependence

The derating factor (0.25-0.4 mA/°C) indicates that the maximum allowable current decreases as ambient temperature rises. Furthermore, luminous intensity for most LEDs decreases with increasing junction temperature. For AlInGaP (yellow), this thermal quenching effect can be more pronounced than for InGaN (green). Proper thermal management on the PCB is advised for high-reliability applications.

5. Mechanical & Package Information

5.1 Pin Assignment

The device has four pins (1, 2, 3, 4).

• Green Chip: Connected to Pins 1 and 3.
• Yellow Chip: Connected to Pins 2 and 4.

This configuration typically allows independent control of each color. The package lens is water clear.

5.2 Package Dimensions and Footprint

The LED conforms to an EIA standard SMD package outline. All dimensions are in millimeters with a standard tolerance of ±0.10mm unless otherwise specified. The datasheet includes detailed dimensional drawings for the component itself and recommended solder pad land patterns to ensure proper soldering and mechanical stability. Following the suggested pad layout is critical for achieving a reliable solder joint and correct alignment during reflow.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profiles

The datasheet provides two suggested infrared (IR) reflow profiles:

1. For Normal Process: A standard profile suitable for tin-lead (SnPb) solder.
2. For Pb-Free Process: A profile designed for higher-temperature lead-free solder alloys (e.g., SAC305). This profile typically has a higher peak temperature (compliant with the 260°C for 5s rating).

The profile includes preheat, thermal soak, reflow, and cooling zones. Controlling the time above liquidus and the peak temperature is vital to prevent damage to the LED package or internal wire bonds.

6.2 Cleaning

If cleaning is necessary after soldering, only specified solvents should be used. The datasheet recommends immersing the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute. Unspecified chemicals may damage the epoxy lens or package material.

6.3 Storage and Handling

• ESD Precautions: LEDs are sensitive to electrostatic discharge (ESD). Handling must include the use of grounded wrist straps, anti-static gloves, and properly grounded workstations. Ionizers are recommended to neutralize static charges.
• Moisture Sensitivity: While not explicitly rated (e.g., MSL), the datasheet recommends that LEDs removed from their original moisture-barrier packaging be reflow-soldered within one week. For longer storage, they should be kept in a sealed container with desiccant or in a nitrogen atmosphere. If stored unpackaged for over a week, a bake at 60°C for 24 hours is recommended before assembly to remove absorbed moisture and prevent "popcorning" during reflow.

7. Packaging & Ordering Information

7.1 Tape and Reel Specifications

The product is supplied in standard embossed carrier tape:

• Reel Size: 7 inches in diameter.
• Quantity per Reel: 4000 pieces.
• Minimum Order Quantity (MOQ): 500 pieces for remainder quantities.
• Tape Width: 8mm.
• The tape is sealed with a top cover tape. Specifications follow ANSI/EIA 481-1-A-1994 standards.

8. Application Notes & Design Considerations

8.1 Drive Circuit Design

LEDs are current-driven devices. The most critical design rule is to use a current-limiting resistor in series with each LED chip.

• Recommended Circuit (Model A): Each LED (or each color chip within the dual LED) has its own dedicated current-limiting resistor connected to the drive voltage. This ensures uniform brightness by compensating for natural variations in the forward voltage (V_F) from one LED to another.
• Not Recommended (Model B): Connecting multiple LEDs directly in parallel with a single shared resistor is discouraged. Small differences in V_F can cause significant current imbalance, leading to uneven brightness and potential overcurrent in the LED with the lowest V_F.

The resistor value (R) is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Use the maximum V_F from the datasheet for a conservative design that guarantees I_F does not exceed the limit even with a low-V_F part.

8.2 Typical Application Scenarios

• Bi-Color Status Indicators: Used in consumer electronics, industrial control panels, and automotive dashboards to show different system states (e.g., power on=green, standby=yellow, fault=alternating).
• Backlighting for Symbols/Icons: Illuminating multi-functional buttons or displays where color denotes function.
• Decorative Lighting: In compact devices where space for multiple single-color LEDs is limited.

9. Technical Comparison & Differentiation

The key differentiator of this component is the integration of two chemically distinct semiconductor materials (InGaN and AlInGaP) in one package. This provides a clear color separation between green and yellow, which can be more difficult to achieve with a single phosphor-converted LED. The independent control of each chip offers design flexibility not available in a pre-mixed bi-color LED with a common anode/cathode. The EIA package ensures a wide industry footprint compatibility.

10. Frequently Asked Questions (FAQs)

10.1 Can I drive both the green and yellow chips simultaneously at their full rated current?

Yes, but you must consider the total power dissipation. If both chips are driven at their max DC current (Green 20mA @ ~3.3V = 66mW, Yellow 30mA @ ~2.0V = 60mW), the combined power is ~126mW. This exceeds the individual Pd ratings (76mW, 75mW) and likely the total package rating. For continuous simultaneous operation, it is advisable to derate the currents to keep the total dissipation within safe limits, especially at elevated ambient temperatures.

10.2 Why is the forward voltage different for the two colors?

The forward voltage is a fundamental property of the semiconductor material's bandgap energy. InGaN (green) has a wider bandgap (~2.4 eV for 525nm) than AlInGaP (yellow, ~2.1 eV for 589nm). A wider bandgap requires more energy for electrons to cross, which manifests as a higher forward voltage under the same current.

10.3 How do I interpret the bin code in the part number?

The bin code for luminous intensity is not embedded in the base part number LTST-C195TGKSKT. The specific intensity bin (e.g., R for green, Q for yellow) is typically indicated on the reel label or in the order documentation. You must consult with the supplier to specify and confirm the desired bin for your order.

11. Practical Design Case Study

Scenario: Designing a dual-status indicator for a 5V USB-powered device. Green indicates "Active," yellow indicates "Charging."

Design Steps:

1. Choose Operating Current: Select I_F = 20mA for both colors for good brightness and longevity.
2. Calculate Current-Limiting Resistors:
   • For Green (use max V_F = 3.5V): R_green = (5V - 3.5V) / 0.020A = 75Ω. Use the nearest standard value (e.g., 75Ω or 82Ω).
   • For Yellow (use max V_F = 2.4V): R_yellow = (5V - 2.4V) / 0.020A = 130Ω. Use 130Ω or 120Ω.
3. Power Rating for Resistors: P = I²R. P_green = (0.02^2)*75 = 0.03W. A standard 1/10W (0.1W) resistor is sufficient.
4. Microcontroller Drive: Connect the cathode pins (via resistors) to GPIO pins of a microcontroller configured as open-drain/source. Driving the pin LOW turns the LED on. Ensure the MCU GPIO can sink/source the 20mA current.
5. PCB Layout: Follow the recommended solder pad dimensions from the datasheet. Ensure adequate clearance between pads. Place the LED away from major heat sources.

12. Operating Principle

Light emission in an LED is based on electroluminescence in a semiconductor p-n junction. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the active region. When these charge carriers recombine, they release energy in the form of photons (light). The wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. InGaN materials are used for shorter wavelengths (blue, green), while AlInGaP materials are used for longer wavelengths (red, orange, yellow). The water-clear epoxy lens encapsulates the chip, provides mechanical protection, and shapes the light output beam.

13. Technology Trends

The development of SMD LEDs like this one is driven by trends towards miniaturization, higher efficiency, and greater integration. Future directions may include:

• Increased Efficiency: Ongoing improvements in epitaxial growth and chip design yield higher luminous efficacy (more light output per electrical watt).
• Color Tuning: Advances in phosphor technology and multi-chip designs enable more precise and stable color points, including tunable white light.
• Improved Thermal Management: New package materials and structures to better dissipate heat, allowing for higher drive currents and maintaining performance at high temperatures.
• Smart Integration: The potential for integrating control ICs (for constant current, color mixing, or addressing) directly with the LED package in system-in-package (SiP) modules.