LTW-270TLA SMD LED Datasheet - Side View - White Light - 10mA - 3.4V Max - English Technical Document

1. Product Overview

The LTW-270TLA is a surface-mount device (SMD) light-emitting diode (LED) engineered specifically for side-emitting illumination applications. Its primary design purpose is to serve as a backlight source for liquid crystal display (LCD) panels, where light needs to be directed laterally across the light guide plate. The device utilizes an InGaN (Indium Gallium Nitride) semiconductor material to produce white light. It is packaged in a standard EIA-compliant format, supplied on 8mm tape mounted on 7-inch diameter reels, making it fully compatible with high-speed automated pick-and-place assembly equipment and standard infrared (IR) reflow soldering processes. The product is compliant with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product.

2. Technical Parameter Deep Dive

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. Key parameters include a maximum power dissipation of 70 mW at an ambient temperature (Ta) of 25°C. The absolute maximum DC forward current is 20 mA. For pulsed operation, a peak forward current of 100 mA is permissible under specific conditions: a 1/10 duty cycle and a pulse width of 0.1 ms. The device can withstand a maximum reverse voltage of 5V, but continuous operation under reverse bias is prohibited. The operating temperature range is from -20°C to +80°C, while the storage temperature range is wider, from -55°C to +105°C. A critical rating for assembly is the infrared soldering condition, which must not exceed 260°C for 10 seconds.

2.2 Electrical & Optical Characteristics

These are the typical performance parameters measured at Ta=25°C and a forward current (IF) of 10 mA, which is the standard test condition. The luminous intensity (Iv) has a minimum of 45 mcd and a typical maximum of 180 mcd. The viewing angle (2θ1/2) is very wide, typically 130 degrees, which is beneficial for achieving uniform backlighting. The forward voltage (VF) ranges from a minimum of 2.8V to a maximum of 3.4V at the test current. The reverse current (IR) is very low, with a maximum of 10 μA when a reverse voltage (VR) of 5V is applied. The chromaticity coordinates, which define the white point color on the CIE 1931 diagram, are typically x=0.31 and y=0.32. It is important to note that a tolerance of ±0.01 should be applied to these chromaticity coordinates. Proper electrostatic discharge (ESD) precautions, such as using grounded wrist straps, are mandatory during handling to prevent damage.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTW-270TLA uses a three-dimensional binning system covering Forward Voltage (VF), Luminous Intensity (IV), and Hue (color coordinates).

3.1 Forward Voltage (VF) Binning

LEDs are classified into three VF bins (2, 3, 4) based on their voltage drop at IF=10 mA. Bin 2 covers 2.80V to 3.00V, Bin 3 covers 3.00V to 3.20V, and Bin 4 covers 3.20V to 3.40V. A tolerance of ±0.1V is applied to each bin.

3.2 Luminous Intensity (IV) Binning

The light output is binned into three categories: P (45.0-71.0 mcd), Q (71.0-112.0 mcd), and R (112.0-180.0 mcd). A tolerance of ±15% is applicable to each intensity bin.

3.3 Hue (Color) Binning

The white color point is precisely controlled through hue bins defined on the CIE 1931 chromaticity diagram. The specified bins are A0, B3, B4, B5, B6, and C0, each representing a specific quadrilateral region on the x,y coordinate plane. A tolerance of ±0.01 applies to the coordinates within each bin. This system allows designers to select LEDs with tightly matched color characteristics for applications requiring uniform white appearance.

4. Mechanical & Packaging Information

4.1 Package Dimensions

The LED comes in a standard SMD package. The detailed mechanical drawing shows all critical dimensions, including body length, width, height, and the placement of the cathode identifier. All dimensions are in millimeters, with a standard tolerance of ±0.10 mm unless otherwise specified. The side-looking lens geometry is a key feature that directs light output parallel to the mounting plane.

4.2 Tape and Reel Packaging

The components are supplied on embossed carrier tape with a width of 8mm. The tape is wound onto a standard 7-inch (178mm) diameter reel. Each reel contains 4000 pieces. The packaging follows ANSI/EIA 481-1-A-1994 specifications. Important notes include: empty pockets are sealed with cover tape, a minimum order quantity of 500 pieces is accepted for remainders, and a maximum of two consecutive missing components is allowed per reel.

4.3 Suggested Solder Pad Layout & Polarity

A recommended land pattern (solder pad footprint) for PCB design is provided to ensure reliable soldering and proper mechanical alignment. The document also indicates the suggested soldering direction relative to the tape feed to optimize the placement process. Clear polarity marking (cathode identification) on the component must be matched with the corresponding pad on the PCB.

5. Soldering & Assembly Guidelines

5.1 Reflow Soldering Profile

A detailed suggested infrared reflow profile is provided. Key parameters include a pre-heat temperature between 150°C and 200°C, a pre-heat time up to 120 seconds maximum, a peak body temperature not exceeding 260°C, and a time at this peak temperature limited to 10 seconds maximum. The LED should not be subjected to more than two reflow cycles under these conditions. It is emphasized that the optimal profile depends on the specific PCB design, solder paste, and oven, so board-level characterization is recommended.

5.2 Hand Soldering

If hand soldering is necessary, it should be performed with a soldering iron tip temperature not exceeding 300°C. The contact time for each lead must be limited to a maximum of 3 seconds, and this should be done only once.

5.3 Cleaning

Cleaning after soldering should only be done if necessary. Only specified chemicals should be used: immersion in ethyl alcohol or isopropyl alcohol at normal temperature for less than one minute is recommended. The use of unspecified chemical liquids can damage the LED package.

6. Storage & Handling

Unopened Packaging: LEDs in their original moisture-proof barrier bag (with desiccant) should be stored at 30°C or less and 90% relative humidity or less. The shelf life under these conditions is one year.
Opened Packaging: Once the moisture barrier bag is opened, the storage environment must not exceed 30°C and 60% relative humidity. It is strongly recommended to complete the IR reflow process within one week of opening. For storage beyond one week, the LEDs should be placed in a sealed container with desiccant or in a nitrogen desiccator. If stored out of the original bag for more than a week, a bake-out at approximately 60°C for at least 20 hours is required before soldering to remove absorbed moisture and prevent \"popcorning\" damage during reflow.

7. Application Notes & Design Considerations

7.1 Target Applications

The primary application for the LTW-270TLA is as a side-firing light source in LCD backlight units (BLUs). Its wide viewing angle helps distribute light evenly into the edge of a light guide plate. It is suitable for ordinary electronic equipment including office automation devices, communication equipment, and household appliances.

7.2 Circuit Design

A current-limiting resistor is essential when driving the LED from a voltage source to set the desired forward current (e.g., 10 mA for testing, up to 20 mA maximum DC). The resistor value can be calculated using Ohm's Law: R = (V_source - VF_LED) / I_LED. The forward voltage (VF) used in the calculation should be the maximum value from the datasheet (3.4V) or the appropriate bin value to ensure the current never exceeds the absolute maximum rating under worst-case conditions.

7.3 Thermal Management

While the device itself has low power consumption, proper thermal design on the PCB is still important for long-term reliability, especially when operating at high ambient temperatures or near maximum current. The derating factor for DC forward current is 0.25 mA/°C above 25°C. This means the allowable continuous current decreases linearly as ambient temperature increases. Ensuring adequate copper area around the solder pads can help dissipate heat.

8. Technical Comparison & Selection Guidance

The key differentiator of the LTW-270TLA is its side-viewing lens geometry, which is distinct from top-view LEDs. When selecting an LED for edge-lit backlighting, a side-view type is mandatory. Designers must compare parameters like luminous intensity (to achieve target brightness), viewing angle (for uniformity), forward voltage (for driver design and power efficiency), and chromaticity bins (for color consistency across multiple LEDs). The wide 130-degree viewing angle is a significant advantage for backlighting. The detailed binning system allows for precise matching of electrical and optical characteristics in arrays, which is critical for preventing visible brightness or color gradients in the final display.

9. Frequently Asked Questions (FAQ)

Q: What is the difference between \"Typical\" and \"Max/Min\" values in the characteristics table?
A: \"Typical\" represents the expected average value under standard test conditions. \"Min\" and \"Max\" define the guaranteed performance limits for all devices; any unit will have a parameter value falling between its specified min and max.

Q: Can I drive this LED with a constant voltage source?
A: No. LEDs are current-driven devices. Their forward voltage has a tolerance and varies with temperature. Driving with a constant voltage (even the \"typical\" VF) can lead to excessive current and rapid failure. Always use a constant current driver or a voltage source with a series current-limiting resistor.

Q: Why is the bin code important?
A: The bin code (e.g., for VF, IV, Hue) tells you the specific performance subset of the LED. For production, ordering LEDs from the same bin ensures consistent brightness, color, and power consumption across all units in your product, which is vital for quality.

Q: How do I interpret the chromaticity diagram and bins?
A: The CIE 1931 diagram maps all perceivable colors. The (x,y) coordinates pinpoint the LED's white point. The bins (A0, B3, etc.) are predefined regions on this map. LEDs from the same bin will emit light of a very similar white color (e.g., cool white, neutral white).

10. Operational Principles & Technology

The LTW-270TLA is based on InGaN semiconductor technology. When a forward voltage exceeding the diode's junction potential is applied, electrons and holes recombine in the active region of the semiconductor, releasing energy in the form of photons (light). The specific composition of the InGaN layers determines the wavelength of the emitted light. To produce white light from a semiconductor that inherently emits blue light, a phosphor coating is typically applied over the blue LED chip. Part of the blue light is converted by the phosphor to longer wavelengths (yellow, red), and the mixture of blue and converted light is perceived by the human eye as white. The side-viewing package incorporates a molded lens that shapes and directs this emitted light laterally.