LTST-S326TGKSKT-5A Dual Color SMD LED Datasheet - Green/Yellow - 5V Reverse Voltage - 20/30mA Forward Current - English Technical Document

1. Product Overview

This document details the technical specifications for a dual-color, side-looking Surface Mount Device (SMD) LED. This component is specifically engineered for applications requiring a compact, right-angle light source, with its primary target market being LCD backlighting modules. Its core advantages include compliance with environmental regulations, high brightness output from advanced semiconductor materials, and compatibility with modern automated assembly and soldering processes.

2. Technical Parameter Deep Dive

2.1 Absolute Maximum Ratings

The device's operational limits are defined at an ambient temperature (Ta) of 25°C. For the green LED (InGaN chip), the maximum continuous forward current is 20 mA, with a peak forward current of 100 mA permissible under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). Its power dissipation is rated at 76 mW. The yellow LED (AlInGaP chip) has a higher continuous forward current rating of 30 mA, a peak of 80 mA, and a power dissipation of 75 mW. Both colors share a maximum reverse voltage of 5V. The operating temperature range is from -20°C to +80°C, with a wider storage range of -30°C to +100°C. The device can withstand infrared reflow soldering at 260°C for 5 seconds.

2.2 Electrical & Optical Characteristics

Measured at Ta=25°C and a test current (IF) of 5 mA, the key performance parameters are as follows. The luminous intensity (Iv) for the green LED has a minimum of 28.0 mcd, typical unspecified, and a maximum of 280.0 mcd. The yellow LED's luminous intensity ranges from a minimum of 7.1 mcd to a maximum of 71.0 mcd. Both LEDs feature a wide viewing angle (2θ1/2) of 130 degrees, typical. The green LED's typical peak emission wavelength (λP) is 530 nm, with a typical dominant wavelength (λd) of 528 nm and a spectral half-width (Δλ) of 35 nm. The yellow LED's corresponding values are 591 nm, 588 nm, and 15 nm, respectively. The forward voltage (VF) is typically 2.80V (max 3.20V) for green and 1.90V (max 2.30V) for yellow at 5 mA. The reverse current (IR) for both is a maximum of 10 μA at VR=5V.

2.3 Thermal Characteristics

The derating factor for the forward current is specified linearly from 25°C. For the green LED, the derating is 0.25 mA/°C, meaning the allowable DC forward current decreases by 0.25 mA for every degree Celsius above 25°C. For the yellow LED, the derating factor is 0.4 mA/°C. This is a critical parameter for ensuring long-term reliability and preventing thermal runaway in the application.

3. Binning System Explanation

The product is sorted into bins based on luminous intensity to ensure consistency in application brightness. For the green LED, bin codes range from N to S, with minimum intensities from 28.0 mcd (N) up to 180.0 mcd (S) and maximums from 45.0 mcd (N) up to 280.0 mcd (S). The yellow LED uses bin codes K through P, with minimums from 7.1 mcd (K) to 45.0 mcd (P) and maximums from 11.2 mcd (K) to 71.0 mcd (P). A tolerance of +/-15% is applied to each intensity bin. This system allows designers to select LEDs with predictable brightness levels for their specific needs.

4. Performance Curve Analysis

While specific graphical curves are not detailed in the provided text, the parameters given allow for inference of key performance trends. The forward voltage (VF) values indicate the IV characteristic curve for each color. The difference in VF (2.80V for green vs. 1.90V for yellow at 5mA) is significant for circuit design, especially when driving both colors from a common voltage source. The spectral half-width data (35nm for green, 15nm for yellow) suggests the yellow LED has a more monochromatic, narrower emission spectrum compared to the broader green emission. The derating factors directly describe the negative temperature dependence of the maximum allowable forward current.

5. Mechanical & Packaging Information

The device conforms to an EIA standard package outline. It is a side-looking (right-angle) package, meaning the primary light emission is parallel to the mounting plane, which is ideal for edge-lighting applications like LCD backlights. The lens material is specified as water clear. The pin assignment is clearly defined: Cathode 1 (C1) is for the yellow AlInGaP chip, and Cathode 2 (C2) is for the green InGaN chip. The component is supplied packaged in 8mm tape on 7-inch diameter reels, compatible with automatic pick-and-place equipment. Detailed dimensional drawings for the package and the recommended soldering pad layout are included in the full datasheet to guide PCB design.

6. Soldering & Assembly Guide

6.1 Reflow Soldering Profiles

Two suggested infrared (IR) reflow profiles are provided: one for normal (tin-lead) solder process and one for Pb-free solder process. The key parameters for the Pb-free process, which uses SnAgCu solder paste, include a preheat stage and a peak temperature condition. The device is confirmed to be compatible with both infrared and vapor phase reflow soldering processes.

6.2 Cleaning

Cleaning must be performed with care. Unspecified chemical liquids should not be used as they may damage the LED package. If cleaning is necessary, it is recommended to immerse the LED in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute.

6.3 Storage Conditions

For optimal shelf life and solderability, LEDs removed from their original, moisture-protective packaging should undergo IR reflow soldering within one week. For longer storage outside the original packaging, they should be kept in a sealed container with desiccant or in a nitrogen ambient. If stored unpackaged for more than a week, a bake-out at approximately 60°C for at least 24 hours is recommended prior to assembly to remove absorbed moisture and prevent "popcorning" during reflow.

7. Packaging & Ordering Information

The standard packaging is 3000 pieces per 7-inch reel. The tape and reel specifications follow ANSI/EIA 481-1-A-1994. Empty component pockets on the carrier tape are sealed with a top cover tape. There is a maximum allowance of two consecutive missing components in the tape. For order quantities that are not multiples of a full reel, a minimum packing quantity of 500 pieces is specified for remainder quantities. The part number LTST-S326TGKSKT-5A follows the manufacturer's internal coding system, which typically encodes package type, color, and bin information.

8. Application Recommendations

8.1 Typical Application Scenarios

The primary and explicitly stated application for this side-looking LED is LCD panel backlighting, where its right-angle emission efficiently couples light into the panel's light guide. Its dual-color capability (green/yellow) can be used for status indicators, multi-color backlighting effects, or in applications requiring specific chromaticity points achievable by mixing these two primary colors.

8.2 Design Considerations

Drive Method: LEDs are current-operated devices. To ensure uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use a current-limiting resistor in series with each individual LED (Circuit Model A). Driving multiple LEDs in parallel directly from a voltage source without individual resistors (Circuit Model B) is discouraged, as slight variations in the forward voltage (VF) characteristics between LEDs can lead to significant differences in current and, consequently, brightness.

Electrostatic Discharge (ESD): The LED is sensitive to electrostatic discharge. Precautions must be taken during handling and assembly: use grounded wrist straps or anti-static gloves, ensure all equipment and work surfaces are properly grounded, and consider using ionizers to neutralize static charges in the work environment.

9. Technical Comparison & Differentiation

This device differentiates itself through its combination of features: a dual-color chip in a single side-looking package. This saves PCB space compared to using two separate LEDs. The use of Ultra Bright InGaN (for green) and AlInGaP (for yellow) chips indicates a focus on high efficiency and luminous output. Its compatibility with automated placement and standard reflow processes (including Pb-free) makes it suitable for high-volume, modern electronics manufacturing. The wide 130-degree viewing angle is optimized for backlighting applications where even illumination is required.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive the green and yellow LEDs simultaneously at their maximum DC current?
A: No. The Absolute Maximum Ratings are for each chip independently. Driving both at 20mA (green) and 30mA (yellow) simultaneously would exceed the package's overall thermal design limits. The total power dissipation must be considered based on the actual forward voltages and currents used.

Q: Why is the forward voltage different for the two colors?
A: The forward voltage is a fundamental property of the semiconductor material's bandgap. InGaN (green) has a larger bandgap than AlInGaP (yellow), resulting in a higher forward voltage required to achieve the same current.

Q: How do I interpret the luminous intensity bin codes?
A: Select the bin code that guarantees your minimum required brightness. For example, if your design needs at least 100 mcd from the green LED, you must specify bin R (112.0-180.0 mcd) or higher. The typical value is not guaranteed, only the min/max range for the selected bin.

Q: Is a heat sink required?
A: For operation at or near the maximum rated current, especially at elevated ambient temperatures, careful thermal management of the PCB is essential. The derating curve must be followed. For low-current operation (e.g., 5-10 mA), a standard PCB layout is usually sufficient.

11. Practical Design & Usage Case

Scenario: Designing a dual-status indicator for a portable device. The LTST-S326TGKSKT-5A can be used to show charging status: yellow for charging, green for fully charged. The designer would place the LED on the edge of the PCB, with its emission side facing a light guide or window in the housing. Two independent current-limiting circuits would be designed—one for the yellow anode (with a resistor calculated for Vsupply, VF_yellow~1.9V, and desired I_F), and one for the green anode (calculated for VF_green~2.8V). The common cathode would be connected to ground. The wide viewing angle ensures the indicator is visible from various angles. The designer must ensure the PCB pad layout matches the recommended pattern to achieve a reliable solder joint and proper alignment.

12. Technical Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor p-n junction devices that emit light through electroluminescence. When a forward voltage is applied, electrons and holes recombine in the active region, releasing energy in the form of photons. The color of the emitted light is determined by the bandgap energy of the semiconductor material. This device incorporates two different semiconductor chips within one package: an Indium Gallium Nitride (InGaN) chip for green emission and an Aluminum Indium Gallium Phosphide (AlInGaP) chip for yellow emission. The side-looking package is achieved through a specific mechanical design that orients the chip's primary light-emitting surface perpendicular to the package leads, directing light out the side of the component.

13. Industry Trends & Context

The development of this component aligns with several key trends in the optoelectronics industry. The move towards RoHS compliance and green products reflects global environmental regulations. The use of high-efficiency materials like InGaN and AlInGaP is driven by the continuous demand for higher brightness and lower power consumption in portable and display devices. Packaging innovations, such as side-looking formats, are crucial for enabling thinner and more compact end products, particularly in consumer electronics like smartphones, tablets, and laptops. Furthermore, compatibility with fully automated, high-speed SMT assembly lines is a fundamental requirement for cost-effective mass production. The inclusion of detailed soldering profiles, especially for Pb-free processes, highlights the industry's transition to more environmentally friendly manufacturing.