LTL-R42FSFAD LED Lamp Datasheet - T-1 Diameter - Amber Diffused Lens - 2.0V Typ - 52mW - English Technical Document

1. Product Overview

The LTL-R42FSFAD is a through-hole mounted LED lamp designed for status indication and signaling applications across a broad range of electronic equipment. It belongs to the category of discrete, radial-leaded indicator LEDs, commonly used where direct PCB mounting and high visibility are required.

1.1 Core Advantages and Product Positioning

This device is engineered for straightforward integration into circuit board assemblies. Its primary advantages include a low power consumption profile coupled with high luminous efficiency, making it suitable for both battery-powered and line-operated devices. The product is constructed as a lead-free component and is fully compliant with RoHS (Restriction of Hazardous Substances) directives, aligning with modern environmental and regulatory standards for electronic manufacturing.

1.2 Target Market and Application Scope

The LED is targeted at applications requiring reliable, long-life visual indicators. Its design flexibility, offered through various intensity and viewing angle specifications, makes it applicable in several key sectors:

• Communication Equipment: Status lights on routers, modems, switches, and other network hardware.
• Computer Peripherals: Power, activity, and mode indicators on external drives, hubs, and input devices.
• Consumer Electronics: Indicator lights on audio/video equipment, home appliances, and personal gadgets.
• Home Appliances: Operational status indicators on white goods and other household devices.

2. Technical Parameter Deep-Dive Analysis

A comprehensive understanding of the electrical and optical parameters is crucial for reliable circuit design and ensuring consistent performance.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed and should be avoided for reliable long-term performance.

• Power Dissipation (Pd): 52 mW maximum. This is the total power the LED package can dissipate as heat.
• DC Forward Current (IF): 20 mA maximum continuous current.
• Peak Forward Current: 60 mA, permissible only under pulsed conditions (duty cycle ≤ 1/10, pulse width ≤ 10µs).
• Thermal Derating: The DC forward current must be derated linearly above 30°C ambient temperature at a rate of 0.27 mA/°C.
• Operating Temperature Range (TA): -30°C to +85°C.
• Storage Temperature Range (Tstg): -40°C to +100°C.
• Lead Soldering Temperature: 260°C for a maximum of 5 seconds, measured 2.0mm (0.079\") from the LED body.

2.2 Electrical & Optical Characteristics at TA=25°C

These are the typical and guaranteed performance parameters under standard test conditions.

• Luminous Intensity (Iv): Ranges from 38 mcd (minimum) to 180 mcd (maximum), with a typical value of 85 mcd at a forward current (IF) of 10 mA. A ±30% testing tolerance is applied to the bin limits.
• Viewing Angle (2θ1/2): 100 degrees. This wide viewing angle, characteristic of a diffused lens, ensures the LED is visible from a broad off-axis position.
• Dominant Wavelength (λd): Specified between 580 nm and 589 nm, with a typical value of 586 nm at IF=10mA. This places the emitted color in the amber/yellow region of the visible spectrum.
• Peak Emission Wavelength (λP): 588 nm, indicating the point of maximum spectral power output.
• Spectral Line Half-Width (Δλ): 15 nm, describing the spectral purity or bandwidth of the emitted light.
• Forward Voltage (VF): Ranges from 1.6V to 2.5V, with a typical value of 2.0V at IF=10 mA.
• Reverse Current (IR): 10 µA maximum when a reverse voltage (VR) of 5V is applied. It is critical to note that this device is not designed for operation under reverse bias; this test condition is for characterization only.

3. Bin Table Specification System

The product is sorted into performance bins to ensure consistency within a production lot. Designers can specify bins to meet tighter application requirements.

3.1 Luminous Intensity Binning

LEDs are categorized based on their measured luminous intensity at 10 mA.

• Bin BC: 38 mcd (Min) to 65 mcd (Max)
• Bin DE: 65 mcd (Min) to 110 mcd (Max)
• Bin FG: 110 mcd (Min) to 180 mcd (Max)
• Note: Tolerance on each bin limit is ±30%.

3.2 Dominant Wavelength Binning

LEDs are also sorted by their dominant wavelength to control color consistency.

• Bin H17: 580 nm (Min) to 584 nm (Max)
• Bin H18: 584 nm (Min) to 589 nm (Max)
• Note: Tolerance on each bin limit is ±1 nm.

The specific bin codes for intensity and wavelength are marked on each packing bag, allowing for traceability and selective use in manufacturing.

4. Performance Curve Analysis

While specific graphical data is referenced in the datasheet, the typical relationships are described below based on standard LED physics and the provided parameters.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The LED exhibits a non-linear I-V characteristic typical of a diode. The forward voltage (VF) has a specified range of 1.6V to 2.5V at 10 mA. This curve is essential for designing the current-limiting circuitry. The voltage will increase slightly with current and decrease with rising junction temperature for a given current.

4.2 Luminous Intensity vs. Forward Current

The luminous intensity (Iv) is approximately proportional to the forward current (IF) over a significant operating range. The specified Iv values are given at IF=10mA. Operating at the maximum continuous current of 20 mA will yield higher light output, but designers must ensure the power dissipation (Pd) limit is not exceeded, considering the resulting forward voltage.

4.3 Temperature Dependence

LED performance is temperature-sensitive. The luminous intensity typically decreases as the junction temperature increases. The datasheet provides a derating factor for current (0.27 mA/°C above 30°C) to manage thermal effects. The forward voltage also has a negative temperature coefficient.

5. Mechanical & Packaging Information

5.1 Outline Dimensions

The LED conforms to the T-1 (3mm) diameter package standard. Key dimensional notes include:

• All dimensions are in millimeters (inches provided for reference).
• Standard tolerance is ±0.25mm (0.010\") unless otherwise specified.
• The maximum protrusion of resin under the flange is 1.0mm (0.04\").
• Lead spacing is measured at the point where the leads emerge from the package body.

5.2 Polarity Identification

Through-hole LEDs typically use lead length or a flat spot on the lens flange to indicate polarity. The longer lead is usually the anode (positive), and the shorter lead is the cathode (negative). The flat spot on the flange is often adjacent to the cathode. Designers must consult the physical sample or detailed drawing for the specific marker used on this component.

6. Soldering & Assembly Guidelines

Proper handling is critical to prevent damage during the assembly process.

6.1 Lead Forming

If leads need to be bent, the bend must be made at a point at least 3mm from the base of the LED lens. The base of the lead frame must not be used as a fulcrum. All forming must be completed before the soldering process and at normal ambient temperature.

6.2 Soldering Process

A minimum clearance of 2mm must be maintained between the base of the lens and the soldering point. Immersing the lens in solder must be avoided.

• Soldering Iron: Maximum temperature 350°C for a maximum of 3 seconds (one time only).
• Wave Soldering: Pre-heat to a maximum of 120°C for up to 100 seconds. Solder wave temperature maximum 260°C for a maximum of 5 seconds.
• Critical Note: Infrared (IR) reflow soldering is explicitly stated as NOT a suitable process for this through-hole type LED lamp. Excessive temperature or time can cause lens deformation or catastrophic failure.

6.3 Storage and Cleaning

For storage, the ambient should not exceed 30°C or 70% relative humidity. LEDs removed from their original packaging should be used within three months. For cleaning, only alcohol-based solvents like isopropyl alcohol should be used if necessary.

7. Packaging and Ordering Information

7.1 Packing Specifications

The LEDs are packaged in bulk quantities:

• Primary packing: 1000, 500, 200, or 100 pieces per anti-static packing bag.
• Secondary packing: 10 packing bags are placed into an inner carton (total 10,000 pcs per inner carton, assuming 1000pc bags).
• Tertiary packing: 8 inner cartons are packed into an outer shipping carton (total 80,000 pcs per outer carton). The last pack in a shipping lot may be a non-full pack.

8. Application Design Recommendations

8.1 Drive Circuit Design

LEDs are current-operated devices. To ensure uniform brightness when driving multiple LEDs, a series current-limiting resistor is mandatory for each LED or each parallel string. The recommended circuit (Circuit A) uses a resistor in series with each LED. Avoid directly connecting multiple LEDs in parallel without individual resistors (Circuit B), as small variances in forward voltage (VF) can cause significant current imbalance and uneven brightness.

The series resistor value (R) can be calculated using Ohm's Law: R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the LED forward voltage (use max value for reliability), and IF is the desired forward current.

8.2 Electrostatic Discharge (ESD) Protection

The LED can be damaged by electrostatic discharge. Precautions must be taken during handling and assembly:

• Use a grounded wrist strap or anti-static gloves.
• Ensure all equipment, workstations, and storage racks are properly grounded.
• Use an ionizer to neutralize static charge that may accumulate on the plastic lens.

8.3 Thermal Management Considerations

While the power dissipation is low, proper PCB layout can help. Ensure adequate spacing from other heat-generating components. Adhering to the current derating curve above 30°C ambient is essential for maintaining reliability, especially in enclosed or high-temperature environments.

9. Technical Comparison & Differentiation

The LTL-R42FSFAD differentiates itself within the through-hole indicator LED market through several key attributes. The use of an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for the 586nm amber chip offers higher efficiency and better temperature stability compared to older technologies like GaAsP. The diffused lens provides a very wide 100-degree viewing angle, making it superior for applications where the viewing position is not fixed directly in front of the LED. Its combination of a typical low forward voltage (2.0V) and clear binning structure for both intensity and wavelength provides designers with predictable performance and the ability to specify for color- or brightness-critical applications.

10. Frequently Asked Questions (FAQ)

10.1 Can I drive this LED at 20 mA continuously?

Yes, 20 mA is the maximum rated continuous DC forward current. However, you must ensure the power dissipation (Pd = VF * IF) does not exceed 52 mW. At 20 mA and a maximum VF of 2.5V, the power would be 50 mW, which is within the limit. Always consider the ambient temperature and apply derating if above 30°C.

10.2 What is the difference between dominant wavelength and peak wavelength?

Peak wavelength (λP) is the single wavelength where the spectral power output is highest. Dominant wavelength (λd) is a calculated value derived from the color coordinates on the CIE chromaticity diagram; it represents the single wavelength of a pure monochromatic light that would match the perceived color of the LED. For design purposes related to color, the dominant wavelength is typically the more relevant parameter.

10.3 Why is a series resistor necessary even if my power supply is current-limited?

A dedicated series resistor provides local, precise current regulation for each LED. It also offers protection against transient voltage spikes and helps balance current in parallel configurations. Relying solely on a global current-limited supply may not prevent current imbalance between LEDs due to VF variations.

11. Practical Design Case Study

Scenario: Designing a status panel with five uniform amber indicators, powered from a 5V DC rail in an environment with a maximum ambient temperature of 40°C.

Design Steps:

1. Current Selection: Target a forward current (IF) of 10 mA for a balance of brightness and longevity.
2. Thermal Derating: At 40°C (10°C above derating start), reduce max current: 20 mA - (10°C * 0.27 mA/°C) = 17.3 mA. Our 10 mA target is safe.
3. Resistor Calculation: Use maximum VF (2.5V) for reliability. R = (5V - 2.5V) / 0.01A = 250 Ω. The nearest standard value (e.g., 240 Ω or 270 Ω) can be used, recalculating the actual current.
4. Circuit Layout: Use the recommended Circuit A: one 240Ω resistor in series with each of the five LEDs, all connected between the 5V rail and ground.
5. Bin Specification: For uniform appearance, specify a single luminous intensity bin (e.g., DE) and a single dominant wavelength bin (e.g., H18) when ordering.
6. PCB Layout: Place LEDs with at least 3mm lead bend radius, ensure 2mm clearance from lens to solder pad, and follow ESD-safe assembly practices.

12. Operating Principle Introduction

The LTL-R42FSFAD operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's turn-on threshold is applied, electrons from the n-type AlInGaP semiconductor recombine with holes from the p-type region. This recombination event releases energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, amber at approximately 586 nm. The diffused epoxy lens surrounding the chip serves to scatter the light, broadening the viewing angle and softening the appearance of the tiny light source.

13. Technology Trends and Context

Through-hole LEDs like the LTL-R42FSFAD represent a mature and highly reliable technology. While surface-mount device (SMD) LEDs dominate new designs for their smaller footprint and suitability for automated pick-and-place assembly, through-hole LEDs maintain significant relevance. Their advantages include superior mechanical bond strength, easier manual prototyping and repair, often higher single-point luminous intensity, and better heat dissipation via the leads. The trend within this segment is towards higher efficiency materials (like AlInGaP used here), tighter performance binning for color and intensity consistency, and unwavering compliance with global environmental standards such as RoHS. They continue to be the preferred choice for applications requiring extreme durability, high visibility in harsh environments, or where through-hole mounting is mandated by design or legacy standards.