LTST-C155KGJRKT Dual Color SMD LED Datasheet - Package Dimensions - Green/Red - 20mA - English Technical Document

1. Product Overview

This document details the specifications for a dual-color, surface-mount device (SMD) LED. The component integrates two distinct AlInGaP semiconductor chips within a single package, enabling the emission of both green and red light. This design is optimized for applications requiring compact, bi-color indication or status display in a minimal footprint. The device is compliant with RoHS directives and is classified as a green product.

The LED is supplied in industry-standard packaging, specifically on 8mm tape wound onto 7-inch diameter reels. This format ensures compatibility with high-speed automated pick-and-place assembly equipment commonly used in modern electronics manufacturing. The package is also designed to withstand standard infrared (IR) and vapor phase reflow soldering processes, facilitating its integration into printed circuit board (PCB) assemblies.

2. Technical Parameter Deep Objective Interpretation

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. For reliable operation, these limits should never be exceeded, even momentarily.

• Power Dissipation (P_D): 75 mW per chip (Green and Red). This parameter limits the total electrical power that can be converted into heat within the LED die. Exceeding this value risks thermal runaway and degradation of the semiconductor material.
• Peak Forward Current (I_FP): 80 mA, specified under a 1/10 duty cycle with a 0.1ms pulse width. This rating is for pulsed operation only and allows for brief periods of high brightness, such as in strobe or signaling applications.
• Continuous Forward Current (I_F): 30 mA DC. This is the maximum steady-state current recommended for continuous operation. It is the primary parameter for designing the LED's drive circuit.
• Current Derating: Linear derating of 0.4 mA/°C from 25°C. As the ambient temperature (T_a) increases, the maximum allowable continuous current must be reduced proportionally to prevent exceeding the junction temperature limit.
• Reverse Voltage (V_R): 5 V. Applying a reverse bias voltage greater than this can cause breakdown and catastrophic failure of the LED chip.
• Operating & Storage Temperature: -55°C to +85°C. The device can be stored and operated within this full industrial temperature range.
• Soldering Temperature Tolerance: The package can withstand wave or IR soldering at 260°C for 5 seconds, or vapor phase soldering at 215°C for 3 minutes, confirming its suitability for lead-free (Pb-free) assembly processes.

2.2 Electrical and Optical Characteristics

These parameters are measured under standard test conditions (T_a=25°C, I_F=20mA) and define the typical performance of the device.

• Luminous Intensity (I_V): The green chip has a typical intensity of 35.0 mcd (millicandela), while the red chip is typically brighter at 45.0 mcd, with a minimum of 18.0 mcd for both. Intensity is measured using a sensor filtered to match the photopic (CIE) human eye response curve.
• Viewing Angle (2θ_1/2): 130 degrees (typical). This wide viewing angle, defined as the full angle where intensity drops to half its on-axis value, makes this LED suitable for applications requiring broad visibility.
• Peak Wavelength (λ_P): Green: 574 nm (typical), Red: 639 nm (typical). This is the wavelength at which the spectral power output is maximum.
• Dominant Wavelength (λ_d): Green: 571 nm (typical), Red: 631 nm (typical). Derived from the CIE chromaticity diagram, this is the single wavelength perceived by the human eye that defines the color of the light.
• Spectral Bandwidth (Δλ): Green: 15 nm (typical), Red: 20 nm (typical). This indicates the spectral purity of the emitted light; a narrower bandwidth indicates a more saturated color.
• Forward Voltage (V_F): 2.0 V (typical), 2.4 V (maximum) for both colors at 20mA. This is a critical parameter for designing the current-limiting circuitry.
• Reverse Current (I_R): 10 µA (maximum) at V_R=5V, indicating good diode characteristics with minimal leakage.
• Capacitance (C): 40 pF (typical) at 0V bias and 1 MHz. This low capacitance is beneficial for high-frequency switching or multiplexing applications.

3. Binning System Explanation

The LEDs are sorted into performance bins to ensure consistency within a production lot. This allows designers to select parts that meet specific intensity or color requirements.

3.1 Luminous Intensity Binning

Both the green and red chips are binned identically for luminous intensity at 20mA. The bin codes (M, N, P, Q) represent ascending ranges of minimum and maximum intensity. For example, bin 'M' covers 18.0 to 28.0 mcd, while bin 'Q' covers 71.0 to 112.0 mcd. A tolerance of ±15% is applied within each bin to account for measurement and production variations.

3.2 Dominant Wavelength Binning (Green Only)

The green LEDs are further binned by dominant wavelength to control color consistency. Three bins are defined: 'C' (567.5-570.5 nm), 'D' (570.5-573.5 nm), and 'E' (573.5-576.5 nm). A tight tolerance of ±1 nm is maintained for each bin, ensuring a uniform green hue across devices from the same bin.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Fig.1, Fig.6), their typical interpretations are crucial for design.

• I-V Curve: The forward voltage (V_F) exhibits a logarithmic relationship with forward current (I_F). A small increase in V_F results in a large increase in I_F, which is why constant-current drive is essential for stable light output.
• Luminous Intensity vs. Current: Intensity is approximately proportional to forward current in the normal operating range (up to the rated continuous current). However, efficiency may drop at very high currents due to increased heat.
• Temperature Characteristics: Luminous intensity typically decreases as junction temperature increases. The forward voltage also has a negative temperature coefficient, meaning V_F decreases slightly as temperature rises. The derating factor of 0.4 mA/°C is applied to manage thermal effects.
• Spectral Distribution: The emission spectrum for AlInGaP LEDs is relatively narrow and Gaussian-shaped, centered around the peak wavelength. The dominant wavelength is calculated from this spectrum and the CIE color matching functions.

5. Mechanical and Packaging Information

5.1 Device and Pin Assignment

The LED features a water-clear lens. The internal dual-color chip has a specific pin assignment: Pins 1 and 3 are assigned to the Green AlInGaP chip, while Pins 2 and 4 are assigned to the Red AlInGaP chip. This configuration allows for independent control of each color.

5.2 Package and Tape/Reel Dimensions

The device conforms to an EIA standard package outline. All dimensions are provided in millimeters with a standard tolerance of ±0.10 mm unless otherwise specified. The component is packaged on 8mm wide embossed carrier tape, which is wound onto 7-inch (approximately 178 mm) diameter reels. Detailed mechanical drawings for the device outline, suggested PCB landing pad pattern, and tape/reel dimensions are included to guide PCB design and assembly setup.

6. Soldering and Assembly Guidelines

6.1 Recommended Reflow Profiles

Two suggested infrared (IR) reflow soldering profiles are provided: one for standard (tin-lead) solder process and one for lead-free (Pb-free) solder process. The lead-free profile is specifically calibrated for use with SnAgCu (tin-silver-copper) solder paste. Key parameters include controlled ramp-up, a defined time above liquidus, a peak temperature (typically 240-260°C max), and a controlled cooling rate to minimize thermal stress on the component.

6.2 Storage and Handling

LEDs should be stored in an environment not exceeding 30°C and 70% relative humidity. Components removed from their original moisture-barrier packaging should be reflow-soldered within one week. For longer storage outside the original packaging, they must be kept in a sealed container with desiccant or in a nitrogen atmosphere. If stored for more than a week, a bake-out at approximately 60°C for at least 24 hours is recommended prior to soldering to remove absorbed moisture and prevent "popcorning" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified alcohol-based solvents like ethyl alcohol or isopropyl alcohol should be used. The LEDs should be immersed at normal temperature for less than one minute. The use of unspecified or aggressive chemical cleaners can damage the plastic lens and package material.

7. Packaging and Ordering Information

The standard packaging is 3000 pieces per 7-inch reel. A minimum order quantity of 500 pieces is applicable for remainder quantities. The tape and reel system conforms to ANSI/EIA-481-1-A specifications. Key tape specifications include: empty component pockets are sealed with cover tape, and a maximum of two consecutive missing components ("missing lamps") is allowed per reel, as per the standard.

8. Application Suggestions

8.1 Typical Application Scenarios

This dual-color LED is ideal for status and indicator applications where space is at a premium and multiple states need to be communicated. Examples include: power/status indicators on consumer electronics (e.g., charging/standby), bi-color signal lights on industrial control panels, status displays on networking equipment, and backlighting for membrane switches or icons requiring two colors.

8.2 Design Considerations and Drive Method

Critical: LEDs are current-operated devices. To ensure uniform brightness, especially when multiple LEDs are connected in parallel, a series current-limiting resistor must be used for each LED or each color channel. The recommended circuit (Circuit A) shows a resistor in series with the LED. Avoid directly connecting multiple LEDs in parallel without individual resistors (Circuit B), as small variations in their forward voltage (V_F) characteristics will cause significant differences in current sharing and, consequently, brightness.

The drive current should be set based on the required brightness and the absolute maximum ratings, considering any necessary derating for elevated ambient temperatures.

8.3 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge. To prevent ESD damage during handling and assembly:

• Personnel should wear grounded wrist straps or anti-static gloves.
• All equipment, workbenches, and storage racks must be properly grounded.
• An ionizer can be used to neutralize static charge that may accumulate on the plastic lens.

9. Technical Comparison and Differentiation

The primary differentiating feature of this component is the integration of two high-performance AlInGaP chips (Green and Red) in a single, compact SMD package. AlInGaP technology offers higher efficiency and better temperature stability for red and amber colors compared to older technologies like GaAsP. The combination of a wide 130-degree viewing angle and independent pin control for each color provides design flexibility not available in single-color LEDs or pre-mixed bi-color LEDs with common anode/cathode. Its compatibility with automated assembly and lead-free reflow processes makes it a modern, manufacturable solution.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive the Green and Red LEDs simultaneously at their full 30mA each?
A: No. The Absolute Maximum Rating for total power dissipation is 75 mW per chip. Driving both at 30mA with a typical V_F of 2.0V results in 60 mW per chip (P=I*V), which is within the limit. However, if the V_F is at its maximum of 2.4V, the power becomes 72 mW, very close to the limit. For reliable long-term operation, especially at higher ambient temperatures, it is advisable to derate the current when driving both colors continuously.

Q: What is the difference between Peak Wavelength and Dominant Wavelength?
A: Peak Wavelength (λ_P) is the physical wavelength where the LED emits the most optical power. Dominant Wavelength (λ_d) is a calculated value based on how the human eye perceives the color of that spectrum. For a monochromatic source, they are identical. For LEDs with some spectral width, λ_d is the single wavelength that would appear to have the same color. λ_d is more relevant for color specification in display applications.

Q: How do I select the correct current-limiting resistor value?
A: Use Ohm's Law: R = (V_supply - V_{F_LED}) / I_{F_desired}. Use the maximum V_F from the datasheet (2.4V) for a conservative design that ensures the current never exceeds the target even with part-to-part variation. For example, with a 5V supply and a target I_F of 20mA: R = (5V - 2.4V) / 0.020A = 130 Ohms. The nearest standard value (e.g., 120 or 150 Ohms) can be used, recalculating the actual current.

11. Practical Design and Usage Case

Case: Dual-Status Indicator for a Portable Device
A designer is creating a compact handheld meter. A single indicator is needed to show three states: Off, Measuring (Green), and Error/Low Battery (Red). Using the LTST-C155KGJRKT saves board space compared to using two separate LEDs.

Implementation: The microcontroller (MCU) has two GPIO pins configured as open-drain outputs. Each pin is connected to the cathode of one color via a current-limiting resistor (calculated as above). The anodes of both LED colors are connected to the system's 3.3V rail. To activate Green, the MCU drives the Green GPIO pin low. To activate Red, it drives the Red GPIO pin low. To turn the LED off, both GPIO pins are set to a high-impedance state. This circuit provides independent control with minimal components.

Consideration: The designer must ensure the MCU's GPIO pins can sink the required LED current (e.g., 20mA). If not, a simple transistor switch can be added. The wide viewing angle ensures the indicator is visible from various angles while holding the device.

12. Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light through electroluminescence. When a forward voltage is applied across the p-n junction, electrons from the n-type region recombine with holes from the p-type region, releasing energy in the form of photons. The wavelength (color) of the emitted light is determined by the energy bandgap of the semiconductor material. This device uses AlInGaP (Aluminum Indium Gallium Phosphide) for both chips, a material system known for high efficiency in the red, orange, amber, and green spectral regions. The "water clear" lens is non-diffused, allowing the intrinsic, highly directional light pattern of the chip to be emitted, resulting in the specified wide viewing angle.

13. Development Trends

The trend in indicator LEDs continues toward higher efficiency (more light output per unit of electrical power), smaller package sizes for denser PCB layouts, and improved color consistency through tighter binning. There is also a growing integration of multiple chips (RGB, dual-color) into single packages to enable multi-color and color-mixing capabilities in a compact form factor. Furthermore, compatibility with increasingly stringent environmental regulations (RoHS, REACH) and high-temperature, lead-free assembly processes remains a fundamental requirement. The development of new semiconductor materials and phosphors continues to expand the color gamut and efficiency of LEDs across the visible spectrum.