LTW-420DS4 White LED Datasheet - 5mm T-1 Package - 3.2V Forward Voltage - 120mW Power Dissipation - English Technical Document

1. Product Overview

The LTW-420DS4 is a white light-emitting diode (LED) designed for through-hole mounting on printed circuit boards (PCBs). It is offered in the popular T-1 (5mm) diameter package with a water-clear lens, making it suitable for a wide range of indicator and illumination applications. The device utilizes InGaN (Indium Gallium Nitride) technology to produce white light.

1.1 Core Advantages

The primary advantages of this LED include its compliance with RoHS (Restriction of Hazardous Substances) directives, indicating it is a lead-free product. It offers high luminous efficiency with relatively low power consumption, making it energy-efficient. The device is designed for compatibility with integrated circuits due to its low current requirements. Its through-hole design allows for versatile mounting on PCBs or panels, providing mechanical stability.

1.2 Target Markets and Applications

This LED is targeted at various electronics sectors. Key application areas include computer peripherals for status indication, communication equipment, consumer electronics, home appliances, and industrial control systems. Its primary function is to serve as a status indicator or a source of low-level illumination in these devices.

2. Technical Parameter Deep Dive

This section provides a detailed, objective analysis of the LED's key electrical, optical, and thermal characteristics as defined in the datasheet.

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. They are not intended for normal operation.

• Power Dissipation (Pd): 120 mW maximum. This is the total power the LED package can dissipate as heat.
• DC Forward Current (IF): 30 mA continuous. Exceeding this current increases the risk of thermal runaway and reduced lifespan.
• Peak Forward Current: 100 mA, but only under pulsed conditions (duty cycle ≤ 1/10, pulse width ≤ 10ms). This is useful for brief, high-intensity flashes.
• Operating Temperature Range (TA): -30°C to +85°C. The LED is guaranteed to function within this ambient temperature range.
• Storage Temperature Range (Tstg): -40°C to +100°C.
• Lead Soldering Temperature: 260°C for a maximum of 5 seconds, measured 2.0mm from the LED body. This is critical for assembly process control.

2.2 Electrical & Optical Characteristics (TA=25°C)

These are the typical performance parameters under standard test conditions.

• Luminous Intensity (Iv): Ranges from a minimum of 1150 mcd to a typical 2200 mcd and a maximum of 5500 mcd at a forward current (IF) of 20 mA. The actual intensity is binned (classified), and a ±15% tolerance is applied to the guaranteed value. The Iv bin code is marked on the packing bag.
• Viewing Angle (2θ1/2): 45 degrees. This is the full angle at which the luminous intensity drops to half of its value at the center (0 degrees). A 45-degree angle provides a relatively wide beam suitable for general indication.
• Forward Voltage (VF): Ranges from 2.8V (min) to 3.2V (typ) to 3.8V (max) at IF=20mA. The forward voltage is also binned, with a measurement allowance of ±0.1V.
• Reverse Current (IR): Maximum 10 μA at a reverse voltage (VR) of 5V. It is explicitly noted that the device is not designed for reverse operation; this parameter is for test purposes only.
• Chromaticity Coordinates (x, y): Typical values are x=0.29, y=0.28 at IF=20mA, derived from the CIE 1931 chromaticity diagram. The specific hue is also binned into defined regions on this diagram.

2.3 Thermal Characteristics

The derating factor for DC forward current is specified as linear from 30°C at a rate of 0.45 mA/°C. This means that for every degree Celsius the ambient temperature rises above 30°C, the maximum allowable continuous forward current must be reduced by 0.45 mA to prevent exceeding the maximum junction temperature and power dissipation limits. For example, at an ambient temperature of 70°C, the maximum DC current would be derated to approximately 30 mA - (0.45 mA/°C * (70-30)°C) = 12 mA.

3. Binning System Explanation

The LED's key parameters are sorted into bins to ensure consistency within a production lot and allow designers to select parts matching specific requirements.

3.1 Luminous Intensity (Iv) Binning

LEDs are classified into three intensity bins: QR (1150-1900 mcd), ST (1900-3200 mcd), and UV (3200-5500 mcd). A ±15% tolerance applies to the bin limits.

3.2 Forward Voltage (VF) Binning

Voltage is binned in 0.2V steps from 2.8V to 3.8V, with codes 2E through 6E. This helps in designing consistent current drive circuits, especially when multiple LEDs are connected in parallel.

3.3 Hue (Chromaticity) Binning

The white color point is binned according to the CIE 1931 chromaticity coordinates. The datasheet defines eight primary hue ranks (A1, A2, B1, B2, C1, C2, D1, D2), each representing a specific quadrilateral area on the chromaticity diagram. A tolerance of ±0.01 is applied to each coordinate limit of these bins. This ensures color consistency among LEDs from the same hue bin.

4. Performance Curve Analysis

While the provided datasheet excerpt mentions typical curves, standard analysis would cover the following relationships, which are crucial for design.

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

An LED is a diode with an exponential I-V characteristic. The curve shows the relationship between the current flowing through the LED and the voltage across it. The \"knee\" voltage is around the typical VF (3.2V). Operating significantly above the knee voltage leads to a rapid increase in current, which must be controlled by an external current-limiting resistor or constant-current driver.

4.2 Luminous Intensity vs. Forward Current

This curve typically shows that luminous intensity increases with forward current, but not necessarily in a perfectly linear fashion, especially at higher currents where efficiency may drop due to heating. The datasheet's Iv rating is specified at 20mA, which is a common operating point.

4.3 Luminous Intensity vs. Ambient Temperature

The light output of an LED generally decreases as the junction temperature increases. Understanding this derating is essential for applications operating in high-temperature environments to ensure sufficient brightness is maintained.

5. Mechanical & Package Information

5.1 Outline Dimensions

The LED is in a T-1 (5mm) radial leaded package. The body diameter is approximately 5mm. The leads are designed for through-hole insertion. The holder/spacer material is specified as black nylon plastic, and the LED lens itself is white. A key mechanical note is that all dimensions have a tolerance of ±0.25mm unless otherwise stated.

5.2 Polarity Identification

For through-hole LEDs, polarity is typically indicated by lead length (the longer lead is the anode, positive) and/or a flat spot on the rim of the plastic lens (usually adjacent to the cathode, negative). The datasheet should be consulted for the specific marking of this model.

6. Soldering & Assembly Guidelines

Proper handling is critical to prevent damage.

6.1 Lead Forming

Leads must be bent at a point at least 3mm away from the base of the LED lens. The base of the lead frame must not be used as a fulcrum. Bending must be performed at room temperature and before the soldering process.

6.2 Soldering Process

Hand Soldering (Iron): Maximum temperature 350°C for a maximum of 3 seconds per lead. The soldering point must be no closer than 2mm from the base of the epoxy lens/bulb. Stress should not be applied to the leads while the LED is hot.
Wave Soldering: Recommended conditions include a pre-heat of up to 100°C for 60 seconds max, a solder wave temperature of 260°C max for 5 seconds max. The dipping position must be no lower than 2mm from the base of the epoxy bulb. Immersing the lens in solder must be avoided.
Important Note: Infrared (IR) reflow soldering is explicitly stated as not suitable for this through-hole type LED product. Excessive temperature or time can deform the lens or cause 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 longer storage outside the original pack, a sealed container with desiccant or a nitrogen ambient is recommended. If cleaning is necessary, alcohol-based solvents like isopropyl alcohol should be used.

7. Packaging & Ordering Information

7.1 Packaging Specification

The LEDs are packed in bags. Standard bag quantities are 1000, 500, 200, or 100 pieces. Ten of these bags are placed into an inner carton, totaling 10,000 pieces. Eight inner cartons are packed into an outer shipping carton, resulting in a total of 80,000 pieces per outer carton. The datasheet notes that in every shipping lot, only the final pack may be a non-full pack.

7.2 Labeling and Identification

The luminous intensity (Iv) bin code is marked on each packing bag, allowing users to identify the performance grade of the contents.

8. Application Recommendations

8.1 Typical Application Circuits

An LED is a current-operated device. To ensure uniform brightness when multiple LEDs are connected in parallel, it is strongly recommended to use a individual current-limiting resistor in series with each LED (Circuit A in the datasheet). Connecting LEDs directly in parallel without individual resistors (Circuit B) is discouraged, as small variations in the forward voltage (VF) between LEDs can cause significant differences in current sharing and, consequently, brightness. The resistor value can be calculated using Ohm's Law: R = (Vsupply - VF) / IF, where VF is the typical or maximum forward voltage from the datasheet, and IF is the desired operating current (e.g., 20mA).

8.2 Design Considerations

• Current Drive: Always use a current-limiting mechanism (resistor or driver).
• Thermal Management: Adhere to power dissipation and current derating rules, especially in high ambient temperatures or enclosed spaces.
• Optical Design: The 45-degree viewing angle is suitable for wide viewing. For more focused light, external lenses or reflectors may be needed.
• PCB Layout: Ensure the hole spacing matches the LED's lead spacing. Provide adequate clearance around the LED body for the 3mm lead bend radius and the 2mm soldering clearance.

9. Technical Comparison & Differentiation

Compared to older technologies like incandescent bulbs, this LED offers vastly superior power efficiency, longer lifetime, and faster switching speeds. Within the LED market, its key differentiators are its specific combination of package (5mm T-1 through-hole), white color, defined intensity and voltage bins, and a 45-degree viewing angle. It is positioned as a general-purpose indicator LED rather than a high-power illumination source.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this LED directly from a 5V supply?
A: No. You must use a series resistor. For example, with a typical VF of 3.2V and a desired IF of 20mA, the resistor value would be (5V - 3.2V) / 0.02A = 90 Ohms. A standard 91 or 100 Ohm resistor would be suitable.

Q: What does the \"±15% tolerance\" on luminous intensity mean?
A: It means the actual measured intensity of an LED from a given bin (e.g., ST bin: 1900-3200 mcd) could be 15% higher or lower than the nominal bin limits. This is a production variation allowance.

Q: Why is lead bending at least 3mm from the body so important?
A: Bending closer to the body creates excessive mechanical stress on the internal wire bonds and the epoxy encapsulation, which can lead to immediate breakage or latent failures over time.

Q: Can I use this LED for outdoor applications?
A: The datasheet states it is good for indoor and outdoor signs. However, for harsh outdoor environments, additional design considerations are needed for waterproofing, UV resistance of external materials, and wider temperature cycling.

11. Practical Use Case Example

Scenario: Designing a status indicator panel for a network router. The panel requires 10 bright white LEDs to indicate power, network activity, and port status. The designer selects the LTW-420DS4 from the UV intensity bin for high visibility. A 5V rail is available on the PCB. The calculation for the series resistor is performed using the maximum VF (3.8V) to ensure the current never exceeds 20mA even with worst-case parts: R = (5V - 3.8V) / 0.02A = 60 Ohms. A 62 Ohm, 1/4W resistor is chosen for each LED. The PCB layout places the LEDs with 2.54mm (0.1\") lead spacing, and the holes are positioned to allow a 5mm bend radius for the leads after insertion. During assembly, a wave soldering process is used with the specified temperature and time profiles, ensuring the solder wave does not contact the LED body.

12. Operating Principle Introduction

An LED is a semiconductor p-n junction diode. When a forward voltage is applied, electrons from the n-type material recombine with holes from the p-type material within the active region. This recombination process releases energy in the form of photons (light). The color (wavelength) of the emitted light is determined by the energy bandgap of the semiconductor material. White LEDs are typically created by using a blue InGaN LED chip coated with a phosphor layer. The blue light from the chip excites the phosphor, which then emits yellow light. The combination of blue and yellow light is perceived by the human eye as white.

13. Technology Trends

The general trend in LED technology is toward higher efficiency (more lumens per watt), higher power density, and better color rendering. For indicator-type LEDs like the LTW-420DS4, trends include miniaturization (smaller packages like 0402 or 0201 surface-mount devices), integration of current-limiting resistors within the package, and the development of LEDs with wider viewing angles or specific beam patterns. The underlying material science continues to improve, yielding more consistent color points and longer operational lifetimes. The move toward RoHS and other environmental compliance standards is now a baseline requirement for electronic components.