Dual Color SMD LED LTST-C155TBJSKT-5A Datasheet - Package 3.2x1.6x1.9mm - Blue/Yellow - Voltage 3.6V/2.4V - Power 76mW/75mW - English Technical Document

1. Product Overview

This document provides the complete technical specifications for a dual-color, surface-mount LED component. The device integrates two distinct semiconductor chips within a single package: an InGaN (Indium Gallium Nitride) chip for blue emission and an AlInGaP (Aluminum Indium Gallium Phosphide) chip for yellow emission. This configuration allows for the generation of two separate colors from one compact footprint, making it suitable for applications requiring status indication, backlighting, or decorative lighting in a space-constrained design. The component is designed to be compatible with automated pick-and-place assembly systems and standard reflow soldering processes, adhering to common industry packaging standards.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

The absolute maximum ratings define the limits beyond which permanent damage to the device may occur. For the blue chip, the maximum continuous DC 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 maximum power dissipation is 76 mW. The yellow chip has a slightly higher continuous current rating of 30 mA but a lower peak current rating of 80 mA and a power dissipation of 75 mW. Both chips share a maximum reverse voltage of 5V, though continuous operation at this voltage is not advised. The operational temperature range is specified from -20°C to +80°C, with a wider storage range of -30°C to +100°C. The device can withstand wave or infrared soldering at 260°C for 5 seconds, or vapor phase soldering at 215°C for 3 minutes.

2.2 Electrical & Optical Characteristics

Key performance parameters are measured at a standard test current of 5 mA and an ambient temperature of 25°C. The luminous intensity for both the blue and yellow chips has a minimum value of 4.50 millicandelas (mcd) and can range up to a maximum of 45.0 mcd, with typical values dependent on the specific bin code. The viewing angle (2θ1/2) is a wide 130 degrees for both colors, indicating a diffuse emission pattern. The blue chip's typical dominant wavelength is 470 nm (peaking at 468 nm) with a spectral half-width of 25 nm, characteristic of InGaN technology. The yellow chip's typical dominant wavelength is 589 nm (peaking at 591 nm) with a narrower 15 nm half-width, typical of AlInGaP. The forward voltage (VF) is typically 3.10V for blue (max 3.60V) and 2.00V for yellow (max 2.40V). Reverse current is limited to a maximum of 10 µA at 5V reverse bias.

3. Binning System Explanation

The product utilizes a binning system to categorize units based on their luminous intensity at the standard 5 mA test current. Both the blue and yellow chips share the same bin code structure. The bins are labeled J, K, L, M, and N. Bin J covers the intensity range from 4.50 mcd to 7.10 mcd. Bin K ranges from 7.10 mcd to 11.20 mcd. Bin L covers 11.20 mcd to 18.00 mcd. Bin M spans 18.00 mcd to 28.00 mcd. The highest output bin, N, includes devices from 28.00 mcd up to the maximum of 45.00 mcd. A tolerance of +/-15% is applied to the limits of each intensity bin. This system allows designers to select components with consistent brightness levels for their application, ensuring visual uniformity in multi-LED arrays.

4. Performance Curve Analysis

While specific graphical data is referenced in the source document (e.g., Figure 1 for peak emission, Figure 6 for viewing angle), typical performance curves for such devices would illustrate several key relationships. The current vs. voltage (I-V) curve would show the exponential relationship characteristic of a diode, with the turn-on voltage being higher for the blue InGaN chip (~3.1V) compared to the yellow AlInGaP chip (~2.0V). Luminous intensity vs. forward current (I-L) curves would demonstrate a near-linear increase in light output with current in the normal operating range, eventually saturating at higher currents due to thermal and efficiency droop. The intensity vs. temperature curve would typically show a decrease in output as junction temperature rises, with the derating factors provided (0.25 mA/°C for blue, 0.4 mA/°C for yellow) allowing for calculation of maximum current at elevated temperatures. The spectral distribution plot would show the narrow emission bands centered around the peak wavelengths.

5. Mechanical & Package Information

5.1 Package Dimensions and Polarity

The device conforms to an industry-standard surface-mount package outline. Key dimensions include a body length, width, and height. The pin assignment is clearly defined: for the part number LTST-C155TBJSKT-5A, pins 1 and 3 are assigned to the blue InGaN chip, while pins 2 and 4 are assigned to the yellow AlInGaP chip. This 4-pin configuration allows for independent electrical control of the two colors. The lens is water clear, which is optimal for maintaining the purity of the emitted colors without introducing tinting.

5.2 Recommended Solder Pad Layout

A suggested land pattern (solder pad design) for PCB layout is provided to ensure reliable solder joint formation during reflow. Adhering to these recommended dimensions helps prevent issues like tombstoning (component standing on end) or insufficient solder fillets, which are critical for mechanical strength and electrical connectivity in automated assembly.

6. Soldering & Assembly Guidelines

6.1 Reflow Soldering Profiles

Two suggested infrared (IR) reflow profiles are detailed: one for standard tin-lead (SnPb) solder process and one for lead-free (Pb-free) solder process, typically using SAC (Sn-Ag-Cu) alloys. The lead-free profile requires a higher peak temperature, as indicated. Both profiles include critical parameters: pre-heat temperature and duration, time above liquidus (TAL), peak temperature, and time within the critical temperature zone. Following these profiles is essential to prevent thermal shock to the LED package, which can cause internal delamination or chip damage, while ensuring proper solder reflow.

6.2 Storage and Handling

LEDs are sensitive to moisture absorption. If removed from their original moisture-barrier packaging, they should undergo reflow soldering within one week. For longer storage outside the original bag, they must be stored in a dry environment, such as a sealed container with desiccant or a nitrogen desiccator. If stored unpackaged for more than a week, a baking procedure (e.g., 60°C for 24 hours) is recommended prior to soldering to drive out absorbed moisture and prevent "popcorning" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable. Harsh or unspecified chemicals can damage the epoxy lens or package material, leading to discoloration, cracking, or reduced light output.

7. Packaging & Ordering Information

The components are supplied packaged in 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Each reel contains 3000 pieces. The tape pockets are sealed with a protective top cover tape. For production efficiency, the packaging follows industry standards (ANSI/EIA 481-1-A), ensuring compatibility with standard automated tape feeders. A minimum packing quantity of 500 pieces is specified for remainder orders. Quality control allows for a maximum of two consecutive missing components in the tape.

8. Application Recommendations

8.1 Typical Application Circuits

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 or each color channel within the dual LED. The provided circuit diagram (Circuit A) shows this configuration: a resistor in series with the LED. Connecting LEDs directly in parallel without individual resistors (Circuit B) is not recommended, as slight variations in the forward voltage (Vf) characteristic between individual LEDs will cause significant current imbalance, leading to uneven brightness and potential over-current in some devices.

8.2 Electrostatic Discharge (ESD) Protection

The semiconductor chips inside the LED are susceptible to damage from electrostatic discharge. Proper ESD control measures must be implemented during handling and assembly. This includes the use of grounded wrist straps, anti-static mats, and ensuring all equipment is properly grounded. The device should be handled in an ESD-protected area.

8.3 Application Scope and Limitations

This LED is designed for use in ordinary electronic equipment such as consumer electronics, office equipment, and communication devices. It is not specifically designed or qualified for applications where high reliability is critical to safety, such as aviation, transportation control, medical life-support systems, or safety devices. For such applications, components with appropriate reliability qualifications must be selected.

9. Technical Comparison & Differentiation

The key differentiating feature of this component is the integration of two distinct color chips (blue and yellow) in one standard SMD package. Compared to using two separate single-color LEDs, this saves PCB space, reduces component count, and simplifies pick-and-place assembly. The use of InGaN for blue and AlInGaP for yellow represents standard, high-efficiency semiconductor technologies for these respective colors, offering good brightness and stability. The wide 130-degree viewing angle provides a diffuse light pattern suitable for panel indication where viewing from oblique angles is required.

10. Frequently Asked Questions (FAQ)

Q: Can I drive both the blue and yellow chips simultaneously at their maximum current?

A: No. The power dissipation ratings (76 mW for blue, 75 mW for yellow) and thermal derating must be considered. Driving both chips at their max DC current (20mA for blue, 30mA for yellow) simultaneously would generate significant heat. The actual permissible currents depend on the PCB's ability to dissipate heat (thermal management) and the ambient temperature. Calculations using the derating factors are necessary.

Q: What is the difference between peak wavelength and dominant wavelength?

A: Peak wavelength (λP) is the wavelength at which the spectral power distribution is maximum. Dominant wavelength (λd) is derived from the CIE chromaticity diagram and represents the single wavelength of a pure monochromatic light that would match the perceived color of the LED. It is the parameter most closely related to human color perception.

Q: Why is a current-limiting resistor necessary even if my power supply is voltage-regulated?

A: An LED's forward voltage has a tolerance and varies with temperature. A voltage source connected directly would attempt to deliver whatever current is needed to achieve that voltage across the diode, which could be excessively high and destroy the LED. The series resistor provides a linear, predictable relationship between supply voltage and LED current, stabilizing the operation.

11. Practical Design Case Study

Consider a design for a dual-status indicator on a network router. A single LTST-C155TBJSKT-5A LED can show blue for "power on/network active" and yellow for "data activity." The microcontroller GPIO pins would control two separate driver circuits. For the blue channel, with a 5V supply (Vcc) and a target current of 10 mA (well below the 20mA max for margin), the series resistor value is calculated as R = (Vcc - Vf_blue) / I = (5V - 3.1V) / 0.01A = 190 Ohms. A standard 200 Ohm resistor would be selected. A similar calculation for the yellow channel at 15 mA: R = (5V - 2.0V) / 0.015A = 200 Ohms. This design uses minimal board space, provides clear, bright indications, and is easily assembled.

12. Operating Principle Introduction

Light Emitting Diodes (LEDs) are semiconductor p-n junction devices that emit light through a process called electroluminescence. 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 a standard diode, this energy is released as heat. In an LED, the semiconductor material (like InGaN or AlInGaP) has a direct bandgap, meaning this energy is released primarily as photons (light). The wavelength (color) of the emitted light is determined by the bandgap energy of the semiconductor material, as described by the equation E = hc/λ, where E is the energy bandgap, h is Planck's constant, c is the speed of light, and λ is the wavelength.

13. Technology Trends

The field of optoelectronics continues to advance with trends focusing on several key areas. Efficiency improvements are ongoing, with research into new material structures (like quantum wells and nanowires) and substrates to reduce internal losses and increase light extraction. Miniaturization remains a driver, pushing packages to smaller footprints and lower profiles while maintaining or improving optical performance. There is also a strong trend towards higher reliability and longer operational lifetimes, especially for applications in automotive lighting and general illumination. Furthermore, the integration of multiple functions, such as combining LEDs with sensors or driver ICs in a single package (system-in-package or SiP), is an area of active development to provide more value and simplify end-system design.