LTST-S320TGKT SMD LED Datasheet - Side Looking - 3.2x2.0x1.1mm - 3.2V - 76mW - Green - English Technical Document

1. Product Overview

The LTST-S320TGKT is a high-performance, side-looking surface-mount device (SMD) light-emitting diode (LED). It utilizes an advanced Indium Gallium Nitride (InGaN) semiconductor chip to produce bright green light. This component is specifically designed for applications where illumination from the side of the component is required, rather than from the top. Its compact EIA-standard package and tape-and-reel packaging make it ideal for high-volume, automated assembly processes common in modern electronics manufacturing.

Key advantages of this LED include its compliance with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product. It features a water-clear lens that maximizes light output and a tin-plated lead frame for excellent solderability. The device is fully compatible with infrared (IR) reflow soldering processes, which is the standard for assembling surface-mount technology (SMT) boards. Its design ensures compatibility with automatic pick-and-place equipment, streamlining the production line.

2. Technical Specifications Deep Dive

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operating the LED under these conditions is not recommended. The maximum power dissipation is 76 milliwatts (mW) at an ambient temperature (Ta) of 25°C. The DC forward current should not exceed 20 mA continuously. For pulsed operation, a peak forward current of 100 mA is permissible under a strict 1/10 duty cycle with a pulse width of 0.1 milliseconds. The device can operate within an ambient temperature range of -20°C to +80°C and can be stored in temperatures from -30°C to +100°C.

2.2 Electro-Optical Characteristics

Measured at a standard test condition of Ta=25°C and a forward current (IF) of 20 mA, the LED exhibits its core performance metrics. The luminous intensity (Iv) has a typical value of 150 millicandelas (mcd), with a minimum specified value of 71.0 mcd. This parameter quantifies the perceived brightness of the light emitted. The viewing angle (2θ1/2), defined as the full angle at which the intensity drops to half of its axial value, is 130 degrees, providing a wide beam pattern suitable for side illumination.

The spectral characteristics are defined by the peak emission wavelength (λP) of 530 nanometers (nm) and a dominant wavelength (λd) of 525 nm. The spectral line half-width (Δλ) is 35 nm, indicating the purity of the green color. Electrically, the forward voltage (VF) typically measures 3.2 volts, with a range from 2.8V to 3.6V. The reverse current (IR) is guaranteed to be 10 microamperes (μA) or less when a reverse voltage (VR) of 5V is applied, though the device is not designed for reverse-bias operation.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into bins based on key parameters. This allows designers to select parts that meet specific tolerance requirements for their application.

3.1 Forward Voltage Binning

Forward voltage is binned in 0.2V steps. Bin codes D7, D8, D9, and D10 correspond to voltage ranges of 2.80-3.00V, 3.00-3.20V, 3.20-3.40V, and 3.40-3.60V, respectively, each with a tolerance of ±0.1V.

3.2 Luminous Intensity Binning

Luminous intensity is categorized into bins Q, R, and S. Bin Q covers 71.0-112.0 mcd, Bin R covers 112.0-180.0 mcd, and Bin S covers 180.0-280.0 mcd. A tolerance of ±15% applies within each bin.

3.3 Dominant Wavelength Binning

The dominant wavelength, which defines the perceived color, is binned as AP (520.0-525.0 nm), AQ (525.0-530.0 nm), and AR (530.0-535.0 nm). The tolerance for each bin is ±1 nm.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Figure 1 for spectral distribution, Figure 5 for viewing angle), their typical behavior can be described. The relationship between forward current (IF) and forward voltage (VF) is exponential, characteristic of a diode. The luminous intensity is approximately proportional to the forward current within the recommended operating range. The peak wavelength may exhibit a slight negative shift (towards shorter wavelengths) with increasing current and a positive shift (towards longer wavelengths) with increasing junction temperature. Understanding these trends is crucial for designing stable and consistent lighting systems.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED conforms to a standard SMD footprint. Key dimensions include a body length, width, and height. The datasheet provides a detailed mechanical drawing with all critical measurements, including lead spacing and overall size, essential for PCB (Printed Circuit Board) land pattern design.

5.2 Polarity Identification and Pad Layout

The component has a clear polarity marking, typically a notch or a dot on the package, indicating the cathode. The datasheet includes a suggested soldering pad dimension drawing to ensure proper solder joint formation and mechanical stability. It also recommends the optimal orientation for the soldering process to prevent tombstoning (where one end lifts off the pad).

6. Soldering and Assembly Guidelines

6.1 IR Reflow Soldering Profile

The device is qualified for lead-free (Pb-free) soldering processes. A suggested reflow profile is provided, adhering to JEDEC standards. Key parameters include a pre-heat zone (150-200°C), a controlled ramp-up, a peak temperature not exceeding 260°C, and a time above 260°C limited to a maximum of 10 seconds. The total pre-heat time should be 120 seconds maximum. This profile must be carefully characterized for the specific PCB assembly to ensure reliability.

6.2 Hand Soldering

If hand soldering is necessary, extreme care must be taken. The soldering iron tip temperature should not exceed 300°C, and the contact time with any lead should be limited to 3 seconds maximum. This should be performed only once to prevent thermal damage to the epoxy package and the semiconductor die.

6.3 Cleaning and Storage

If cleaning is required after soldering, only specified alcohol-based solvents like isopropyl alcohol or ethyl alcohol should be used. Immersion should be at normal temperature for less than one minute. Unspecified chemicals can damage the package. For storage, unopened moisture-proof bags should be kept at ≤30°C and ≤90% Relative Humidity (RH). Once opened, LEDs should be stored at ≤30°C and ≤60% RH and used within one week. For longer storage out of the original bag, baking at 60°C for at least 20 hours before soldering is recommended to remove absorbed moisture and prevent \"popcorning\" during reflow.

7. Packaging and Ordering Information

The LEDs are supplied on 8mm wide embossed carrier tape wound onto 7-inch (178mm) diameter reels. Each reel contains 3000 pieces. The tape pockets are sealed with a protective top cover tape. Packaging follows ANSI/EIA-481 specifications. For remnant quantities, a minimum packing quantity of 500 pieces applies.

8. Application Notes and Design Considerations

8.1 Typical Application Scenarios

This side-looking LED is ideal for applications requiring edge-lighting or status indication from the side of a device. Common uses include backlighting for membrane switches, side illumination for LCD displays in handheld devices, status indicators on the bezels of consumer electronics (like routers, set-top boxes), and backlighting for symbols or text on front panels.

8.2 Circuit Design

A current-limiting resistor is mandatory when driving the LED from a voltage source. The resistor value (R) can be calculated using Ohm's Law: R = (V_supply - VF) / IF, where VF is the forward voltage of the LED (use max value for a conservative design) and IF is the desired forward current (e.g., 20 mA). Driving the LED with a constant current source is preferred for optimal brightness and color consistency, especially over temperature variations.

8.3 Thermal Management

Although the power dissipation is low, proper thermal design on the PCB is important for long-term reliability. Ensuring adequate copper area around the LED pads helps dissipate heat and maintains a lower junction temperature, which preserves luminous output and lifespan.

8.4 ESD (Electrostatic Discharge) Precautions

LEDs are sensitive to electrostatic discharge. Handling procedures should include the use of grounded wrist straps, anti-static mats, and conductive containers. All assembly equipment must be properly grounded.

9. Technical Comparison and Differentiation

The primary differentiator of this component is its side-emitting optical design, which is distinct from the more common top-emitting SMD LEDs. Compared to older technologies like AlGaInP (for red/yellow), the InGaN chip offers higher efficiency and brightness in the green/blue spectrum. The 130-degree viewing angle provides very wide illumination, which is advantageous for applications requiring light spread along a surface. Its compatibility with standard IR reflow processes places it in line with modern SMT assembly, unlike older through-hole LEDs which require wave soldering.

10. Frequently Asked Questions (FAQ)

Q: Can I drive this LED without a current-limiting resistor?
A: No. An LED is a current-driven device. Connecting it directly to a voltage source will cause excessive current to flow, instantly destroying it. Always use a series resistor or a constant-current driver.

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. λd is more relevant for color specification.

Q: Can I use this LED for continuous operation at 20mA?
A: Yes, 20mA is the recommended continuous DC forward current. However, ensure the ambient temperature and PCB thermal design allow the junction temperature to stay within safe limits to maintain specified performance and longevity.

Q: Why is storage condition so important for SMD LEDs?
A: The plastic epoxy package can absorb moisture from the air. During the high-temperature reflow soldering process, this trapped moisture can vaporize rapidly, creating internal pressure that can crack the package or delaminate the chip—a phenomenon known as \"popcorning.\" Proper storage and baking prevent this.

11. Practical Application Example

Scenario: Designing a side-lit status indicator for a wireless router. The LED needs to be mounted on the main PCB, which is assembled using a lead-free IR reflow process. The light should shine through a small window on the side of the router's plastic casing to indicate \"power on\" and \"network activity\" (blinking).

Implementation: The LTST-S320TGKT is selected for its side emission and green color. Two LEDs are placed near the edge of the PCB, aligned with the light pipes in the casing. The PCB land pattern is designed according to the datasheet's suggested pad dimensions. A 150Ω current-limiting resistor is calculated for a 5V supply (using VF_max=3.6V, IF=20mA: R = (5-3.6)/0.02 = 70Ω, a 150Ω provides a safer ~9mA). The microcontroller's GPIO pin drives the LED through this resistor. The assembly follows the specified reflow profile, and the finished product provides clear, wide-angle side illumination.

12. Technology Principle Introduction

This LED is based on InGaN semiconductor technology. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region. Their recombination releases energy in the form of photons (light). The specific composition of the Indium Gallium Nitride alloy in the quantum well structure determines the bandgap energy, and consequently, the wavelength (color) of the emitted light—in this case, green at around 530nm. The side-looking feature is achieved through the chip placement within the package and the shaping of the reflector cup and epoxy lens, which directs the primary light output laterally.

13. Industry Trends

The trend in SMD LEDs continues towards higher efficiency (more lumens per watt), smaller package sizes for higher density applications, and improved color consistency through tighter binning. There is also a growing emphasis on reliability under harsh conditions (higher temperature, humidity) for automotive and industrial applications. Furthermore, the integration of control electronics directly with the LED die (e.g., for addressable RGB LEDs) is a significant development, though for simple indicator LEDs like this one, the focus remains on cost-effectiveness, reliability, and compatibility with automated high-speed assembly lines.