Side View SMD LED 57-21 Series Datasheet - Package Dimensions 2.0x1.25x0.7mm - Forward Voltage 2.0V - Luminous Intensity 51mcd - Yellow Green Color - English Technical Document

1. Product Overview

The 57-21 series represents a family of side-viewing surface-mount device (SMD) light-emitting diodes (LEDs). These components are designed for applications where space is constrained and a wide viewing angle is required. The series is available in several colors, including the specific yellow-green variant detailed in this document, which utilizes an AlGaInP (Aluminum Gallium Indium Phosphide) semiconductor chip material.

The core advantages of this series stem from its package design. It incorporates a wide viewing angle, typically 120 degrees, which is achieved through an optimized inter-reflector design. This feature significantly enhances light coupling efficiency, making these LEDs particularly suitable for use with light pipes, a common component in backlighting assemblies. Furthermore, their low forward current requirement (20mA for typical operation) makes them ideal for battery-powered or other power-sensitive portable electronic equipment.

The target market and primary applications include office automation (OA) equipment, backlighting for full-color liquid crystal displays (LCDs), automotive interior lighting, and as replacements for conventional indicator bulbs or small fluorescent lamps in various electronic devices.

2. In-Depth Technical Parameter Analysis

2.1 Absolute Maximum Ratings

These ratings define the limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• Reverse Voltage (V_R): 5V. Exceeding this voltage in reverse bias can cause junction breakdown.
• Forward Current (I_F): 25mA DC. The continuous DC current should not surpass this value.
• Peak Forward Current (I_FP): 60mA. This is permissible only under pulsed conditions with a duty cycle of 1/10 at 1kHz.
• Power Dissipation (P_d): 60mW. This is the maximum allowable power loss within the device.
• Operating & Storage Temperature: Ranges from -40°C to +85°C (operating) and -40°C to +100°C (storage).
• Electrostatic Discharge (ESD): Withstands 2000V per the Human Body Model (HBM), indicating a moderate level of ESD robustness for handling.
• Soldering Temperature: Compatible with reflow soldering at 260°C for 10 seconds or hand soldering at 350°C for 3 seconds.

2.2 Electro-Optical Characteristics

These parameters are measured at a standard test condition of an ambient temperature (T_a) of 25°C and a forward current (I_F) of 20mA.

• Luminous Intensity (I_v): The typical value is 51 millicandelas (mcd), with a minimum of 32 mcd. A tolerance of ±11% applies to the luminous intensity.
• Viewing Angle (2θ_1/2): 120 degrees. This is the full angle at which the luminous intensity drops to half of its peak value.
• Peak Wavelength (λ_p): 575 nanometers (nm). This is the wavelength at which the spectral power distribution is maximum.
• Dominant Wavelength (λ_d): 573 nm. This is the single wavelength perceived by the human eye as the color of the light, with a tight tolerance of ±1 nm.
• Spectral Bandwidth (Δλ): 20 nm. This indicates the range of wavelengths emitted, centered around the peak wavelength.
• Forward Voltage (V_F): Typically 2.0V, ranging from a minimum of 1.7V to a maximum of 2.4V at 20mA, with a tolerance of ±0.1V.
• Reverse Current (I_R): Maximum of 10 microamperes (μA) when a reverse voltage of 5V is applied.

3. Binning System Explanation

The product utilizes a three-code binning system to categorize variations in key parameters, allowing designers to select LEDs with consistent performance for their application.

• CAT (Luminous Intensity Rank): This code groups LEDs based on their measured luminous intensity output.
• HUE (Dominant Wavelength Rank): This code categorizes the LEDs according to their precise dominant wavelength, ensuring color consistency.
• REF (Forward Voltage Rank): This code sorts the LEDs by their forward voltage drop at the test current.

These codes are printed on the product packaging and reel labels, enabling precise matching during the assembly process for applications requiring uniform brightness or color.

4. Performance Curve Analysis

The datasheet provides several characteristic curves that illustrate device behavior under varying conditions.

• Relative Luminous Intensity vs. Forward Current: This curve shows how light output increases with current. It is generally linear in the normal operating range but will saturate at very high currents.
• Relative Luminous Intensity vs. Ambient Temperature: This graph demonstrates the thermal quenching effect common in LEDs, where luminous efficiency decreases as the junction temperature rises. The output typically declines as temperature increases from -40°C to +100°C.
• Forward Voltage vs. Forward Current: This is the standard I-V curve for a diode, showing the exponential relationship. The typical V_F of 2.0V is read from this curve at 20mA.
• Forward Current Derating Curve: This crucial graph specifies the maximum allowable continuous forward current as a function of the ambient temperature. As temperature rises, the maximum current must be reduced to prevent overheating and ensure reliability.
• Radiation Pattern: A polar diagram visually represents the 120-degree viewing angle, showing the angular distribution of light intensity.
• Spectrum Distribution: A plot of relative intensity versus wavelength, centered at 575nm with a 20nm bandwidth, confirming the yellow-green color point.

5. Mechanical and Packaging Information

5.1 Package Dimensions

The LED features a compact side-view SMD package. Key dimensions (in millimeters, with a general tolerance of ±0.1mm unless specified) include a body length of approximately 2.0mm, a width of 1.25mm, and a height of 0.7mm. Detailed drawings show the anode and cathode pad locations, overall shape, and recommended footprint for PCB layout.

5.2 Polarity Identification

The component has a marked polarity. The cathode is typically indicated by a visual marker such as a notch, a dot, or a green tint on the corresponding side of the lens or package. Correct orientation is essential during assembly.

5.3 Reel and Tape Packaging

The LEDs are supplied on embossed carrier tape for automated pick-and-place assembly. The tape width, pocket pitch, and dimensions are specified. Each reel contains 2000 pieces. The reel itself has defined flange and hub dimensions. The packaging includes moisture-resistant measures: the reels are sealed inside an aluminum moisture-proof bag along with a desiccant and a humidity indicator card to protect the devices from ambient moisture during storage and transport.

6. Soldering and Assembly Guidelines

Reflow Soldering: The device is rated for lead-free reflow soldering profiles with a peak temperature of 260°C for up to 10 seconds. It is critical to follow the recommended temperature ramp-up, soak, and cool-down rates to prevent thermal shock and ensure reliable solder joints.

Hand Soldering: If manual soldering is necessary, the iron tip temperature should not exceed 350°C, and contact time should be limited to 3 seconds per pad. Use a low-power iron and avoid applying excessive mechanical stress.

Storage Conditions: To maintain solderability, the devices should be stored in their original moisture-barrier bags below 30°C and 60% relative humidity. Once the bag is opened, the components should be used within a specified time frame (typically 168 hours at factory conditions) or baked according to standard IPC/JEDEC guidelines before reflow.

7. Packaging and Ordering Information

The standard ordering unit is a reel of 2000 pieces. The product label on the reel provides essential information including the Part Number (PN), Customer Part Number (CPN), quantity (QTY), lot number (LOT NO), and the three critical binning codes: CAT, HUE, and REF. The label also indicates RoHS and Pb-free compliance.

8. Application Recommendations

8.1 Typical Application Scenarios

• LCD Backlighting: The side-view geometry and wide angle make it perfect for edge-lighting thin LCD panels in mobile phones, tablets, and instrument clusters.
• Light Pipe Illumination: The optimized light coupling efficiently injects light into acrylic or polycarbonate light guides for status indicators or symbolic backlighting.
• Portable Device Indicators: Low current consumption is ideal for battery-powered devices like Bluetooth headsets, remote controls, and handheld medical devices.
• Automotive Interior Lighting: Can be used for backlighting buttons, switches, and small displays on dashboards and center consoles.

8.2 Design Considerations

• Current Limiting: Always use a series resistor or constant current driver to limit the forward current to the desired value (e.g., 20mA for typical brightness). Calculate the resistor value using R = (V_supply - V_F) / I_F.
• Thermal Management: While power dissipation is low, ensure adequate PCB copper area or thermal vias under the LED pads, especially in high ambient temperature environments or when driving near maximum ratings, to help dissipate heat and maintain performance and longevity.
• ESD Protection: Implement standard ESD precautions during handling and assembly. Consider adding transient voltage suppression (TVS) diodes or other protection on sensitive lines if the LED is connected to external interfaces.

9. Technical Comparison and Differentiation

Compared to standard top-view SMD LEDs, the key differentiator of the 57-21 series is its side-viewing form factor, which enables lighting from the edge of a PCB. Compared to other side-view LEDs, its advantages include the specific AlGaInP technology for high-efficiency yellow-green light, a very wide 120-degree viewing angle optimized for light pipes, and clearly defined binning for color and intensity consistency. The combination of low V_F and good luminous intensity results in high luminous efficacy for its class.

10. Frequently Asked Questions (FAQs)

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λ_p) is the physical peak of the emitted light spectrum. Dominant wavelength (λ_d) is the single wavelength that would produce the same color perception to the human eye. For LEDs, λ_d is often the more relevant specification for color matching.

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, potentially destroying it instantly. A series resistor or active current regulator is mandatory.

Q: How does ambient temperature affect performance?
A: As temperature increases, the forward voltage (V_F) decreases slightly, but the luminous intensity drops more significantly (thermal quenching). The derating curve must be followed for maximum current. High temperatures also accelerate long-term degradation.

Q: What do the CAT, HUE, and REF codes mean for my design?
A: If your application requires uniform appearance (e.g., a row of status lights), you should specify tight bins for HUE (color) and CAT (brightness). For simple on/off indicators, standard bins may be sufficient. The REF code helps in designing consistent current drive circuits.

11. Practical Design and Usage Examples

Example 1: Mobile Phone Keypad Backlighting
A designer uses four 57-21 series LEDs placed along the edge of a PCB underneath a translucent keypad. The wide 120-degree viewing angle ensures even illumination across all keys. The LEDs are driven in series with a constant current of 18mA (slightly below typical to extend battery life and reduce heat) using a dedicated LED driver IC that includes PWM dimming control from the phone's main processor.

Example 2: Industrial Panel Indicator
In a factory control panel, a red 57-21 LED (from the same series family) is paired with a custom-molded acrylic light pipe to bring an "Error" status indicator from a densely packed PCB to a front-panel label. The side-view package fits perfectly in the constrained space behind the panel. The designer selects LEDs from a single HUE bin to ensure the red color matches other indicators on the panel.

12. Technology Principle Introduction

This LED is based on AlGaInP semiconductor technology. When a forward voltage is applied across the p-n junction, electrons and holes are injected into the active region where they recombine. In AlGaInP materials, this recombination releases energy in the form of photons (light) with wavelengths in the yellow, orange, red, and green spectrum, depending on the exact composition of the alloy. The yellow-green color (573nm dominant wavelength) is achieved by carefully controlling the ratios of aluminum, gallium, indium, and phosphorus during crystal growth. The emitted light is then shaped and directed by the epoxy lens and internal reflector structure of the package to achieve the desired viewing angle.

13. Industry Trends and Developments

The trend in SMD indicator LEDs continues towards higher efficiency (more light output per mA), improved color consistency through tighter binning, and increased miniaturization while maintaining or improving optical performance. There is also a growing demand for higher reliability grades, especially for automotive and industrial applications, which may involve extended temperature ranges and more stringent reliability testing. The side-view form factor remains essential for backlighting increasingly thin consumer electronics and automotive displays. Furthermore, integration with onboard control, such as incorporating a chip resistor or a simple IC for constant current operation within the package, is an emerging trend to simplify circuit design.