LTST-C195TBKGKT Dual Color SMD LED Datasheet - Blue & Green - 20mA & 30mA Forward Current - English Technical Document

1. Product Overview

The LTST-C195TBKGKT is a dual-color, surface-mount device (SMD) 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 blue emission and an AlInGaP (Aluminum Indium Gallium Phosphide) chip for green emission. This configuration allows for the creation of multiple colors or status indicators from a single component footprint.

Key advantages of this LED include its compliance with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product. It is packaged on 8mm tape wound onto 7-inch diameter reels, making it fully compatible with high-speed automated pick-and-place assembly equipment. The device is also designed to be compatible with common soldering processes, including infrared (IR) and vapor phase reflow.

2. Technical Parameters Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended for extended periods.

• Power Dissipation: Blue Chip: 76 mW, Green Chip: 75 mW (at Ta=25°C).
• Peak Forward Current: Blue: 100 mA, Green: 80 mA. This is specified under pulsed conditions (1/10 duty cycle, 0.1ms pulse width) to handle brief current surges.
• DC Forward Current: The maximum continuous forward current is 20 mA for the blue chip and 30 mA for the green chip.
• Current Derating: The maximum allowable DC forward current decreases linearly with increasing ambient temperature. The derating factor is 0.25 mA/°C for blue and 0.4 mA/°C for green, starting from 25°C.
• Reverse Voltage: Both chips have a maximum reverse voltage rating of 5V. Continuous operation under reverse bias is prohibited.
• Temperature Range: Operating: -20°C to +80°C. Storage: -30°C to +85°C.
• Soldering Temperature Tolerance: The device can withstand wave or infrared soldering at 260°C for 5 seconds, and vapor phase soldering at 215°C for 3 minutes.

2.2 Electrical & Optical Characteristics

These are typical performance parameters measured at an ambient temperature of 25°C under specified test conditions.

• Luminous Intensity (Iv): Measured at a forward current (IF) of 20mA.
  • Blue: Minimum 28.0 mcd, Typical value not specified, Maximum 180 mcd.
  • Green: Minimum 18.0 mcd, Typical value not specified, Maximum 112 mcd.
• Viewing Angle (2θ1/2): The full angle at which luminous intensity is half the axial value. Typical for both colors is 130 degrees, indicating a wide viewing pattern.
• Peak Wavelength (λP): The wavelength at which the emitted optical power is greatest. Typical: Blue: 468 nm, Green: 574 nm.
• Dominant Wavelength (λd): The single wavelength perceived by the human eye that defines the color. Typical: Blue: 470 nm, Green: 571 nm.
• Spectral Bandwidth (Δλ): The width of the emission spectrum at half its maximum power. Typical: Blue: 25 nm, Green: 15 nm.
• Forward Voltage (VF): Measured at IF=20mA.
  • Blue: Typical 3.4V, Maximum 3.8V.
  • Green: Typical 2.0V, Maximum 2.4V.
• Reverse Current (IR): Maximum 10 µA for both chips when a reverse voltage (VR) of 5V is applied.
• Capacitance (C): Typical 40 pF for the green chip (measured at VF=0V, f=1MHz). Not specified for blue.

3. Binning System Explanation

To ensure consistency in applications, LEDs are sorted (binned) based on their measured luminous intensity. The LTST-C195TBKGKT uses separate bin codes for its blue and green chips.

3.1 Blue Chip Intensity Bins

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

3.2 Green Chip Intensity Bins

• Bin M: 18.0 - 28.0 mcd
• Bin N: 28.0 - 45.0 mcd
• Bin P: 45.0 - 71.0 mcd
• Bin Q: 71.0 - 112.0 mcd

A tolerance of +/-15% is applied to the intensity range of each bin. This system allows designers to select LEDs with predictable brightness levels for their specific application needs.

4. Performance Curve Analysis

The datasheet references typical performance curves which are essential for understanding device behavior under varying conditions. While the specific graphs are not reproduced in the text, they typically include:

• Relative Luminous Intensity vs. Forward Current: Shows how light output increases with current, usually in a near-linear relationship until saturation.
• Forward Voltage vs. Forward Current: Demonstrates the diode's I-V characteristic, crucial for designing current-limiting circuits.
• Relative Luminous Intensity vs. Ambient Temperature: Illustrates the decrease in light output as junction temperature rises, highlighting the importance of thermal management.
• Spectral Distribution: Graphs showing the relative power emitted across different wavelengths, centered around the peak and dominant wavelengths.

These curves are vital for predicting performance in real-world applications where temperature and drive current may vary.

5. Mechanical & Packaging Information

The device conforms to a standard EIA package outline. Key dimensional notes include:

• All dimensions are provided in millimeters, with a default tolerance of ±0.10 mm unless otherwise specified.
• The lens is water clear.
• Pin Assignment: The dual-color functionality is achieved through a 4-pin configuration.
  • Pins 1 and 3 are assigned to the Blue (InGaN) chip.
  • Pins 2 and 4 are assigned to the Green (AlInGaP) chip.
• The datasheet includes detailed package dimension drawings, suggested soldering pad layout dimensions, and tape & reel packaging drawings to guide PCB design and assembly.

6. Soldering & Assembly Guide

6.1 Reflow Soldering Profiles

Two suggested infrared (IR) reflow 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 designed for use with Sn-Ag-Cu (SAC) solder paste. Adherence to these time-temperature profiles is critical to prevent thermal damage to the LED package or internal wire bonds.

6.2 Cleaning

Unspecified chemical cleaners should be avoided as they may damage the LED package. If cleaning is necessary, immersion in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is recommended.

6.3 Storage Conditions

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

7. Packaging & Ordering Information

• The LEDs are supplied on 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels.
• Standard reel quantity is 4000 pieces.
• A minimum packing quantity of 500 pieces is available for remainder lots.
• The packaging follows ANSI/EIA-481-1-A standards. Empty pockets in the tape are sealed with a cover tape.
• The maximum allowable number of consecutive missing components on a reel is two.

8. Application Suggestions

8.1 Typical Application Scenarios

This dual-color LED is suitable for a wide range of applications including status indicators, backlighting for small displays, decorative lighting, panel illumination, and consumer electronics where space is at a premium and multi-color indication is beneficial.

8.2 Design Considerations & Drive Method

Critical: LEDs are current-operated devices. To ensure uniform brightness when driving multiple LEDs in parallel, a current-limiting resistor must be placed in series with each LED. This compensates for minor variations in the forward voltage (Vf) characteristic between individual devices. Driving LEDs in parallel without individual resistors (Circuit B in the datasheet) can lead to significant brightness differences and potential current hogging by the LED with the lowest Vf.

8.3 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge. Precautions must be taken during handling and assembly:

• Use a grounded wrist strap or anti-static gloves.
• Ensure all workstations, tools, and equipment are properly grounded.
• Follow standard ESD control procedures to prevent latent or catastrophic damage.

9. Technical Comparison & Differentiation

The primary differentiation of the LTST-C195TBKGKT lies in its dual-chip, 4-pin design within a standard SMD footprint. This offers significant space savings compared to using two separate single-color LEDs. The use of InGaN for blue and AlInGaP for green provides high efficiency and good color purity for each channel. The wide 130-degree viewing angle makes it suitable for applications requiring broad visibility.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive the blue and green chips simultaneously at their maximum DC current?
A: No. The power dissipation ratings (76mW blue, 75mW green) and thermal design of the package must be considered. Simultaneous operation at max current may exceed the total package power handling capability or cause excessive junction temperature rise, leading to reduced lifetime or failure. Derating with temperature must be applied.

Q: Why is the forward voltage different for the blue and green chips?
A: This is due to the fundamental material properties of InGaN and AlInGaP semiconductors. The bandgap energy of InGaN is higher, requiring a higher voltage to achieve the same current flow, which correlates to the higher typical Vf of 3.4V for blue versus 2.0V for green.

Q: What does the bin code on the reel label mean for my design?
A: The bin code indicates the guaranteed minimum and maximum luminous intensity for the LEDs on that reel. For consistent brightness across a product line, specify and use LEDs from the same intensity bin. Mixing bins may result in visible brightness variations.

11. Practical Design Case Study

Scenario: Designing a compact status indicator for a device that needs to show "Standby" (Green), "Active" (Blue), and "Fault" (alternating Blue/Green).
Implementation: A single LTST-C195TBKGKT can fulfill all three states. A microcontroller with two GPIO pins can independently control the blue and green channels via simple transistor switches or dedicated LED driver ICs. Individual current-limiting resistors must be calculated for each channel based on the desired drive current and the supply voltage, using the typical Vf values (3.4V for Blue, 2.0V for Green) as a starting point for calculation, while ensuring the circuit can accommodate the maximum Vf. This design saves PCB space and component count compared to a two-LED solution.

12. Operating Principle Introduction

Light emission in an LED is a phenomenon called electroluminescence. When a forward voltage is applied across the p-n junction of a semiconductor chip (exceeding its bandgap voltage), electrons and holes are injected into the junction region. These charge carriers recombine, releasing energy in the form of photons (light). The color (wavelength) of the emitted light is determined by the bandgap energy of the semiconductor material. InGaN materials are used for shorter wavelengths (blue, violet, green), while AlInGaP materials are used for longer wavelengths (red, orange, yellow, green). The "water clear" lens does not color the light but helps in shaping the beam and protecting the chip.

13. Technology Trends

The development of SMD LEDs like this device is driven by trends towards miniaturization, higher efficiency, and greater integration in electronics. The use of materials like InGaN and AlInGaP represents mature, high-efficiency technology platforms. Ongoing research focuses on improving quantum efficiency (more light out per electrical power in), achieving higher power densities in smaller packages, enhancing color rendering, and developing novel packaging techniques for better thermal management and reliability. The integration of multiple chips or even microcontrollers within a single package ("smart LEDs") is also a growing trend for advanced lighting and indication applications.