SMD3528 White LED Datasheet - Size 3.5x2.8mm - Voltage 3.2V - Power 0.108W - English Technical Document

1. Product Overview

The SMD3528 is a surface-mount white light-emitting diode (LED) designed for general lighting applications. This single-chip LED offers a compact footprint and is suitable for backlighting, indicator lights, and decorative lighting. The core advantage of this component lies in its standardized package size, which facilitates automated assembly processes and ensures compatibility with common PCB layouts. The target market includes consumer electronics, automotive interior lighting, and commercial signage manufacturers seeking reliable and cost-effective illumination solutions.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Electrical Characteristics

The LED's performance is characterized under standard test conditions (T_s=25°C). The key parameters define its operational limits and typical behavior.

2.1.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. Operation outside these limits is not advised.

• Forward Current (I_F): 30 mA (Continuous)
• Forward Pulse Current (I_FP): 60 mA (Pulse width ≤10ms, Duty cycle ≤1/10)
• Power Dissipation (P_D): 108 mW
• Operating Temperature (T_opr): -40°C to +80°C
• Storage Temperature (T_stg): -40°C to +80°C
• Junction Temperature (T_j): 125°C
• Soldering Temperature (T_sld): Reflow soldering at 200°C or 230°C for 10 seconds.

2.1.2 Typical Technical Parameters

These values represent the expected performance under normal operating conditions.

• Forward Voltage (V_F): 3.2 V (Typical), 3.6 V (Maximum) at I_F=20mA
• Reverse Voltage (V_R): 5 V
• Reverse Current (I_R): 10 μA (Maximum)
• Viewing Angle (2θ_1/2): 120° (Typical)

3. Binning System Explanation

The product is classified into bins to ensure color and brightness consistency within an application. The binning is defined by the product naming rule.

3.1 Model Number Structure

The model number T3200SL(C,W)A follows a specific coding system that defines its attributes. While the full code breakdown is provided in the source, key elements include the chip count (S for single small-power chip), package code (32 for 3528), and color code (C for Neutral White, W for Cool White).

3.2 Correlated Color Temperature (CCT) Binning

The white light is available in several standard CCT bins, each associated with a specific chromaticity region on the CIE diagram.

• 2725K ±145K (Bin: 27M5)
• 3045K ±175K (Bin: 30M5)
• 3985K ±275K (Bin: 40M5)
• 5028K ±283K (Bin: 50M5)
• 5665K ±355K (Bin: 57M7)
• 6530K ±510K (Bin: 65M7)

Note: Orders specify a minimum luminous flux bin, not a maximum. Products shipped may exceed the ordered flux value but will always adhere to the specified CCT chromaticity region.

3.3 Luminous Flux Binning

Flux is binned according to CCT and Color Rendering Index (CRI). The tables define minimum and typical values at 20mA. For example, a 70 CRI Neutral White (3700-5300K) LED has bins like B6 (7.0-7.5 lm min), B7 (7.5-8.0 lm min), B8 (8.0-8.5 lm min), and B9 (8.5-9.0 lm min). Higher CRI versions (80 and 90) have correspondingly lower flux bins due to the phosphor system trade-off.

3.4 Forward Voltage Binning

To aid in current matching for series connections, the forward voltage is also binned. Codes range from B (2.8-2.9V) to J (3.5-3.6V), with a measurement tolerance of ±0.08V.

3.5 Chromaticity Regions

Each CCT bin corresponds to an elliptical region on the CIE 1931 chromaticity diagram. The specification provides the center coordinates (x, y), the lengths of the semi-major (b) and semi-minor (a) axes, and the ellipse rotation angle (Φ). These ellipses are defined according to ANSI C78.377 standards (5-step or 7-step MacAdam ellipses), ensuring the light from LEDs within the same bin appears uniform in color to the human eye.

4. Performance Curve Analysis

4.1 Current-Voltage (I-V) Characteristic Curve

The forward voltage increases non-linearly with forward current. Designers must use this curve to select appropriate current-limiting resistors or driver circuits to ensure stable operation and prevent exceeding the maximum current rating.

4.2 Relative Luminous Flux vs. Forward Current

The light output increases with current but will eventually saturate. Operating significantly above the recommended 20mA test current may lead to reduced efficiency and accelerated lumen depreciation due to increased junction temperature.

4.3 Spectral Power Distribution (SPD)

The relative spectral energy curve shows the emission spectrum of the white LED, which is a combination of blue light from the semiconductor chip and broader yellow/red light from the phosphor coating. The curve shifts slightly with changes in CCT: warmer whites (2600-3700K) have more energy in the longer (red) wavelengths, while cooler whites (5000-10000K) have a more prominent blue peak.

4.4 Junction Temperature vs. Relative Spectral Energy

As the junction temperature rises, the efficiency of the phosphor and the chip itself can change, potentially causing a shift in the SPD and a slight change in perceived color (chromaticity shift) and a decrease in light output. Proper thermal management is crucial for maintaining consistent performance.

5. Mechanical and Package Information

5.1 Package Dimensions

The SMD3528 package has nominal dimensions of 3.5mm in length and 2.8mm in width. The exact dimensional drawing with tolerances is provided: .X dimensions have a tolerance of ±0.10mm, and .XX dimensions have a tolerance of ±0.05mm.

5.2 Pad Layout and Stencil Design

A recommended land pattern (footprint) for PCB design is supplied, along with a corresponding stencil pattern for solder paste application. Adhering to these recommendations ensures reliable solder joint formation during reflow.

5.3 Polarity Identification

The component has a cathode mark (typically a green line, notch, or other marking on the package) to indicate polarity. Correct orientation is essential for circuit operation.

6. Soldering and Assembly Guidelines

6.1 Moisture Sensitivity and Baking

The SMD3528 LED is classified as moisture-sensitive according to IPC/JEDEC J-STD-020C. If the original moisture barrier bag is opened and the components are exposed to ambient humidity, they must be baked before reflow soldering to prevent "popcorning" or internal damage during the high-temperature process.

• Baking Condition: 60°C for 24 hours.
• Post-Baking: Components should be soldered within 1 hour or stored in a container with <20% relative humidity.
• Do Not bake at temperatures above 60°C.

6.2 Reflow Soldering Profile

The LED can withstand standard reflow soldering profiles with a peak temperature of 200°C or 230°C for a maximum of 10 seconds. The specific profile (ramp-up rate, soak time, peak temperature, cooling rate) should be optimized for the entire assembly but must stay within these limits.

6.3 Storage Conditions

• Unopened Package: Store at 5-30°C, humidity <85%.
• Opened Package: Store at 5-30°C, humidity <60%. For long-term storage of opened packages, it is strongly recommended to use a sealed container with desiccant or a nitrogen atmosphere to prevent moisture absorption.

7. Packaging and Ordering Information

7.1 Packaging Specification

The LEDs are typically supplied on tape and reel for automated pick-and-place machines. The specific reel size, pocket count, and tape width conform to industry standards (e.g., EIA-481).

7.2 Ordering Model Number

The complete model number, such as T3200SLWA, must be specified to obtain the desired combination of attributes: package (3528), chip type, color (Cool White), and internal code. Contacting the manufacturer is necessary for non-standard combinations of flux and CCT.

8. Application Suggestions

8.1 Typical Application Scenarios

• Backlighting: For LCD panels in appliances, industrial controls, and automotive dashboards.
• General Indicator Lights: Status indicators on electronic devices.
• Decorative Lighting: Accent lighting in consumer products.
• Signage and Channel Letters: Low-power illumination for indoor signs.

8.2 Design Considerations

• Current Driving: Always use a constant current driver or a current-limiting resistor. Do not connect directly to a voltage source.
• Thermal Management: Although low-power, ensure the PCB has adequate thermal relief, especially when operating at or near the maximum current. High ambient temperatures will reduce light output and lifespan.
• Optical Design: The 120° viewing angle provides wide illumination. For focused beams, secondary optics (lenses) are required.
• Binning for Consistency: For applications requiring uniform appearance, specify tight CCT and flux bins. Using LEDs from different bins in the same product may result in visible color or brightness differences.

9. Technical Comparison

The SMD3528 is a legacy package that has been largely superseded by more efficient packages like the 2835 and 3030. Its primary differentiation lies in its widespread availability, low cost, and extensive historical use in designs. Compared to newer packages, it generally has lower luminous efficacy (lumens per watt) and may have a larger thermal resistance. However, for cost-sensitive applications or direct replacements in existing products, it remains a viable option.

10. Frequently Asked Questions (Based on Technical Parameters)

10.1 What is the difference between the CCT bins (e.g., 27M5 vs. 30M5)?

The number (27, 30) refers to the nominal correlated color temperature divided by 100 (e.g., 2700K, 3000K). The letter/number combination (M5, M7) refers to the size of the chromaticity ellipse on the CIE diagram, with M7 representing a larger allowable color variation than M5. A tighter bin (M5) ensures better color consistency.

10.2 Can I drive this LED at 30mA continuously?

While the absolute maximum rating is 30mA, the typical test condition and most performance data are specified at 20mA. Operating at 30mA will produce more light but will also generate significantly more heat, potentially reducing lifespan and causing chromaticity shift. It is advisable to design for a lower operating current (e.g., 15-20mA) for reliability and efficiency.

10.3 Why is baking necessary, and how do I know if my LEDs need it?

The plastic package can absorb moisture from the air. During reflow soldering, this moisture turns to steam rapidly, potentially causing delamination or cracks. Check the humidity indicator card inside the moisture barrier bag immediately upon opening. If the card shows a humidity level higher than the specified threshold (e.g., 10% or 30%, depending on the sensitivity level), or if the bag has been open for an extended period in a humid environment, baking is required.

10.4 How do I interpret the luminous flux bin code (e.g., B7)?

The flux bin code (A9, B1, B2... B9) defines a range of minimum luminous flux values. For example, a B7 bin for a 70 CRI Neutral White LED guarantees a minimum flux of 7.5 lumens at 20mA, with a typical value up to 8.0 lumens. The actual shipped parts will be at or above the minimum value for that bin.

11. Practical Design Case

11.1 Designing a Constant Current LED Array

Consider designing a light panel using 20 SMD3528 LEDs in a series-parallel configuration. To ensure uniform brightness, LEDs from the same CCT and flux bin should be used. If the chosen bin has a typical V_F of 3.2V at 20mA, and a 24V DC power supply is available, you could arrange 10 LEDs in series (10 * 3.2V = 32V, which exceeds 24V). A better configuration might be 5 strings of 4 LEDs in series. Each string would drop approximately 12.8V (4 * 3.2V). A current-limiting resistor for each string would be calculated as R = (V_supply - V_string) / I_F = (24V - 12.8V) / 0.020A = 560 Ω. The power dissipated in each resistor would be P = I²R = (0.02)² * 560 = 0.224W, so a 0.25W or 0.5W resistor is recommended. This design provides redundancy (if one LED fails open, only its string goes out) and helps manage voltage tolerances across the LEDs.

12. Principle Introduction

A white SMD LED operates on the principle of electroluminescence in a semiconductor material, combined with phosphor conversion. A chip, typically made of indium gallium nitride (InGaN), emits blue light when forward biased. This blue light is partially absorbed by a layer of phosphor material (e.g., yttrium aluminum garnet doped with cerium, YAG:Ce) coated on or around the chip. The phosphor absorbs the blue photons and re-emits light across a broad spectrum in the yellow region. The mixture of the remaining blue light and the converted yellow light is perceived by the human eye as white. The exact ratio of blue to yellow light, controlled by the phosphor composition and thickness, determines the correlated color temperature (CCT) of the emitted white light.

13. Development Trends

The general trend in LED technology is toward higher efficacy (more lumens per watt), improved color rendering, and higher reliability at lower cost. For packages in this size category, the industry has largely migrated to the 2835 package footprint, which often offers better thermal performance and higher light output in a similarly sized envelope. There is also a continuous drive to improve the phosphor systems for higher Color Rendering Index (CRI) values, especially R9 (saturated red), and to achieve more consistent color over angle and temperature. Furthermore, the integration of LEDs with intelligent drivers and controls for tunable white (adjustable CCT) is a growing application trend, though this typically requires multi-chip packages.