LTST-C155KSKRKT Dual Color SMD LED Datasheet - Package Dimensions - Red/Yellow - 30mA - English Technical Document

1. Product Overview

The LTST-C155KSKRKT is a dual-color, surface-mount LED designed for modern electronic applications requiring compact size and reliable performance. This device integrates two distinct AlInGaP semiconductor chips within a single package: one emitting in the red spectrum and the other in the yellow spectrum. This configuration allows for the creation of bi-color indicators or simple multi-state signaling without the need for multiple discrete components. The LED is packaged on 8mm tape and supplied on 7-inch reels, making it compatible with high-speed automated pick-and-place assembly equipment commonly used in volume manufacturing.

Key advantages of this product include its compliance with environmental regulations, high luminous intensity output from its advanced AlInGaP chip technology, and a wide viewing angle that ensures good visibility from various angles. Its primary target markets include consumer electronics, industrial control panels, automotive interior lighting, and general-purpose status indication where space is at a premium and reliable performance is required.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the stress limits beyond which permanent damage to the device may occur. For the red and yellow chips, the maximum continuous forward current (DC) is rated at 30 mA. The peak forward current, permissible under pulsed conditions (1/10 duty cycle, 0.1ms pulse width), is significantly higher at 80 mA. The maximum power dissipation for each chip is 75 mW. A critical parameter for circuit design is the derating factor of 0.4 mA/°C, which indicates that the permissible DC forward current must be reduced linearly as the ambient temperature rises above 25°C to prevent overheating. The maximum reverse voltage is 5V for both colors. The device is rated for operation within an ambient temperature range of -30°C to +85°C and can be stored between -40°C and +85°C.

2.2 Electrical and Optical Characteristics

Under standard test conditions (Ta=25°C, IF=20 mA), the LED exhibits specific performance metrics. The luminous intensity (Iv) for the red chip has a typical value of 45.0 mcd (millicandelas), with a minimum specified value of 18.0 mcd. The yellow chip is typically brighter, with a luminous intensity of 75.0 mcd and a minimum of 28.0 mcd. Both chips share a typical forward voltage (Vf) of 2.0V, with a maximum of 2.4V at 20 mA. This relatively low forward voltage is beneficial for low-power circuit design. The viewing angle (2θ1/2) is a wide 130 degrees for both colors, providing a broad emission pattern. The peak emission wavelength (λp) is typically 639 nm for red and 591 nm for yellow, while the dominant wavelength (λd) is typically 631 nm and 589 nm, respectively. The spectral line half-width (Δλ) is 15 nm, indicating a relatively pure color emission. Other parameters include a maximum reverse current (Ir) of 10 μA at 5V and a typical capacitance (C) of 40 pF.

3. Binning System Explanation

The product utilizes a binning system to categorize LEDs based on their luminous intensity, ensuring consistency within a production batch. For the red chip, bins are labeled M, N, P, and Q, with minimum-to-maximum intensity ranges of 18.0-28.0 mcd, 28.0-45.0 mcd, 45.0-71.0 mcd, and 71.0-112.0 mcd, respectively. The yellow chip uses bins N, P, Q, and R, covering ranges from 28.0-45.0 mcd up to 112.0-180.0 mcd. A tolerance of +/-15% is applied to each intensity bin. This system allows designers to select the appropriate brightness grade for their application, balancing cost and performance requirements. The datasheet does not indicate separate binning for wavelength or forward voltage for this specific part number.

4. Performance Curve Analysis

While the provided text excerpt references typical characteristic curves on page 6, the specific graphs are not included in the text. Typically, such datasheets include curves illustrating the relationship between forward current and luminous intensity (I-Iv curve), forward current and forward voltage (I-V curve), and the effect of ambient temperature on luminous intensity. These curves are essential for designers to understand the non-linear behavior of the LED. For instance, the I-Iv curve shows that luminous intensity increases with current but may saturate at higher currents. The I-V curve is crucial for selecting the appropriate current-limiting resistor. Temperature derating curves visually demonstrate how maximum permissible current decreases with rising ambient temperature, which is critical for ensuring long-term reliability in thermally challenging environments.

5. Mechanical and Package Information

The LED is provided in a surface-mount package. The exact physical dimensions of the component itself are detailed in the package dimensions drawing (referenced on page 1 of the datasheet). The device is supplied in a tape-and-reel format compatible with automated assembly. The tape width is 8mm, and it is wound on a standard 7-inch (178mm) diameter reel. Each reel contains 3000 pieces of the LED. For orders that are not a full reel, a minimum packing quantity of 500 pieces applies for remainders. The packaging conforms to ANSI/EIA 481-1-A-1994 specifications. The tape has embossed pockets for the components, which are sealed with a top cover tape. The maximum allowed number of consecutive missing components in the tape is two.

6. Soldering and Assembly Guide

6.1 Soldering Profiles

The datasheet provides detailed soldering condition recommendations to prevent thermal damage. For infrared (IR) reflow soldering, a specific temperature profile is suggested. The peak temperature should not exceed 260°C, and the time above this temperature should be limited to a maximum of 5 seconds. A pre-heat stage is also recommended. Separate profiles are suggested for normal solder processes and for lead-free (Pb-free) processes, the latter requiring solder paste with SnAgCu composition. For wave soldering, a maximum solder wave temperature of 260°C for up to 10 seconds is specified, with a pre-heat limit of 100°C for 60 seconds max. For manual soldering with an iron, the tip temperature should not exceed 300°C, and contact time should be limited to 3 seconds per joint, for one time only.

6.2 Storage and Handling

Proper storage is critical for maintaining solderability. LEDs should be stored in an environment not exceeding 30°C and 70% relative humidity. If removed from their original moisture-barrier packaging, they should undergo IR reflow soldering within one week. For longer storage outside the original bag, they must be kept in a sealed container with desiccant or in a nitrogen desiccator. Components stored unpackaged for more than a week require a baking process at approximately 60°C for at least 24 hours before assembly to remove absorbed moisture and prevent "popcorning" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Unspecified chemicals may damage the LED package. The recommended method is to immerse the LED in ethyl alcohol or isopropyl alcohol at normal room temperature for less than one minute. Aggressive or ultrasonic cleaning is not advised unless specifically tested and qualified.

7. Application Suggestions

7.1 Typical Application Scenarios

This dual-color LED is ideal for applications requiring status indication with more than one state. Common uses include power/standby indicators (e.g., red for standby, yellow for on), fault/warning indicators, battery charge status indicators, and mode selection feedback in consumer devices like routers, chargers, audio equipment, and small appliances. Its wide viewing angle makes it suitable for front-panel applications where the user may view the indicator from an angle.

7.2 Design Considerations and Drive Method

LEDs are current-driven devices. To ensure uniform brightness, especially when multiple LEDs are used in parallel, it is strongly recommended to use a series current-limiting resistor for each LED (Circuit Model A). Driving multiple LEDs in parallel without individual resistors (Circuit Model B) is discouraged because small variations in the forward voltage (Vf) characteristic of each LED can cause significant differences in the current flowing through each one, leading to uneven brightness. The drive circuit must be designed to limit the current to the maximum DC rating of 30 mA per chip, considering the derating factor if the operating ambient temperature is above 25°C.

7.3 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge. To prevent ESD damage during handling and assembly, the following precautions are essential: Personnel should wear conductive 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 due to friction during handling. These measures are critical for maintaining high production yield and product reliability.

8. Technical Comparison and Differentiation

The primary differentiating feature of this component is the integration of two high-efficiency AlInGaP chips in one compact SMD package. AlInGaP technology offers higher luminous efficacy and better temperature stability compared to older technologies like GaAsP for red and yellow colors. The dual-color capability reduces the component count and board space compared to using two separate single-color LEDs. The wide 130-degree viewing angle is another competitive advantage for applications requiring off-axis visibility. The detailed binning system provides designers with predictable optical performance.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive both the red and yellow chips simultaneously at their full 30mA current?
A: No. The Absolute Maximum Ratings specify 30mA DC per chip. Driving both simultaneously at full current would likely exceed the total package power dissipation limits and cause overheating. The drive circuit must be designed to manage the total power.

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λp) is the wavelength at which the emission spectrum has its highest intensity. Dominant wavelength (λd) is derived from the CIE chromaticity diagram and represents the single wavelength that best matches the perceived color of the light as seen by the human eye. λd is often more relevant for color specification.

p>Q: How do I select the correct current-limiting resistor?
A: Use Ohm's Law: R = (Vsupply - Vf_LED) / I_LED. Use the maximum Vf from the datasheet (2.4V) for a conservative design to ensure current never exceeds the desired level even with part-to-part variation. For example, with a 5V supply and a target current of 20mA: R = (5V - 2.4V) / 0.020A = 130 Ohms. Use the next standard value, e.g., 130 or 150 Ohms, and calculate the actual power dissipation in the resistor (P = I^2 * R).

10. Practical Design and Usage Case

Consider designing a dual-status indicator for a network switch. The goal is to show link status (steady yellow) and activity (blinking red). The LTST-C155KSKRKT is perfect for this. Two independent microcontroller GPIO pins can be used to drive the LED through separate current-limiting resistors. Pin 1 and 3 would be connected for the yellow anode/cathode, and pins 2 and 4 for the red. The design must ensure the microcontroller pins can sink/source enough current (e.g., 20mA per color). If the switch operates in a warm environment (e.g., 50°C inside an enclosure), the forward current must be derated. The derated current = 30mA - [0.4 mA/°C * (50°C - 25°C)] = 30mA - 10mA = 20mA. Therefore, designing for 20mA from the start provides a safe margin for elevated temperature operation.

11. Operating Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor devices that emit light when an electric current passes through them. This phenomenon is called electroluminescence. In the AlInGaP (Aluminum Indium Gallium Phosphide) material system used in this LED, when a forward voltage is applied across the p-n junction, electrons from the n-type region and holes from the p-type region are injected into the active region. When these electrons and holes recombine, they release energy in the form of photons (light). The specific wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material. AlInGaP has a bandgap suitable for producing high-efficiency red, orange, and yellow light. The dual-color package simply houses two such semiconductor chips with different material compositions (bandgaps) inside a single encapsulant, with separate electrical connections for independent control.

12. Technology Trends

The general trend in LED technology for indicator applications continues toward higher efficiency, smaller package sizes, and lower power consumption. AlInGaP remains the dominant technology for high-performance red, orange, and yellow LEDs due to its superior efficacy and stability. Integration, as seen in this dual-color device, is a key trend to save PCB space and simplify assembly in increasingly miniaturized electronics. There is also a growing emphasis on precise binning and tighter tolerances to meet the demands of applications requiring consistent color and brightness, such as in automotive clusters or consumer electronics where aesthetic uniformity is important. Furthermore, compatibility with lead-free and high-temperature soldering processes is now a standard requirement for all components used in modern electronics manufacturing.