LTD-3812SW-P LED Display Datasheet - 0.3-inch Digit Height - White Color - 5mA Forward Current - English Technical Document

1. Product Overview

The LTD-3812SW-P is a surface-mount device (SMD) designed as a dual-digit numeric display. Its primary function is to provide clear, high-visibility numeric readouts in electronic equipment. The core technology is based on InGaN (Indium Gallium Nitride) white LED chips mounted on a sapphire substrate. This combination yields a display with a black face and white segments, offering excellent contrast for easy readability.

1.1 Key Features and Advantages

The display is engineered for performance and reliability in modern electronics. Its feature set addresses common requirements for indicator and display applications.

• Digit Size: Features a 0.3-inch (7.62 mm) character height, making it suitable for applications where space is limited but readability is crucial.
• Optical Quality: Offers continuous, uniform segments for a consistent visual appearance, high brightness, and a wide viewing angle.
• < strong>Efficiency and Reliability: Requires low power to operate and is built with solid-state reliability, ensuring long service life.
• Standardization: Devices are categorized (binned) for luminous intensity and chromaticity, allowing for consistent performance in batch production.
• Environmental Compliance: The package is lead-free and compliant with RoHS (Restriction of Hazardous Substances) directives.

2. Technical Specifications Deep Dive

This section provides a detailed, objective analysis of the device's operational limits and performance characteristics under defined conditions.

2.1 Absolute Maximum Ratings

These values represent the stress limits beyond which permanent damage to the device may occur. Operation at or near these limits is not recommended for reliable performance.

• Power Dissipation per Segment: 35 mW maximum.
• Peak Forward Current per Segment: 50 mA (under pulsed conditions: 1/10 duty cycle, 0.1ms pulse width).
• Continuous Forward Current per Segment: 10 mA at 25°C. This rating derates linearly at 0.11 mA/°C as ambient temperature (Ta) increases above 25°C.
• Temperature Ranges: Operating and storage temperature range is -35°C to +105°C.
• Soldering Tolerance: The device can withstand iron soldering at 260°C for 3 seconds, with the iron tip positioned at least 1/16 inch below the seating plane.

2.2 Electrical and Optical Characteristics

These are the typical performance parameters measured at an ambient temperature (Ta) of 25°C and a forward current (IF) of 5 mA, which is the standard test condition.

• Luminous Intensity (IV): Ranges from a minimum of 71 mcd to a maximum of 165 mcd per chip. The intensity is measured using a sensor-filter combination that approximates the photopic (CIE) eye-response curve.
• Chromaticity Coordinates (x, y): Defined on the CIE 1931 chromaticity diagram. The typical values provided are x=0.294 and y=0.286, indicating a white point.
• Forward Voltage (VF): Per chip, typically between 2.7V and 3.2V at 5mA.
• Reverse Current (IR): Maximum of 100 µA at a reverse voltage (VR) of 5V. This parameter is for test purposes only; the LED is not designed for continuous reverse bias operation.
• Luminous Intensity Matching: The ratio of intensity between segments in a similar lit area is 2:1 or better, ensuring uniform appearance.
• Cross Talk: Specified to be ≤ 2.5%, minimizing unwanted illumination of adjacent off segments.

2.3 Electrostatic Discharge (ESD) Sensitivity

Like most semiconductor devices, these LEDs are susceptible to damage from electrostatic discharge. The datasheet strongly recommends standard ESD prevention practices: using grounded wrist straps or anti-static gloves, ensuring all workstations and equipment are properly grounded, and employing ionizers to neutralize static charges that may accumulate on the plastic package during handling.

3. Binning System Explanation

To ensure consistency, the LEDs are sorted into bins based on key parameters. This allows designers to select parts with tightly grouped characteristics for their application.

3.1 Forward Voltage (VF) Binning

LEDs are categorized into bins (3 through 7) based on their forward voltage drop at 5mA. Each bin has a 0.1V range (e.g., Bin 3: 2.70V-2.80V, Bin 4: 2.80V-2.90V), with a tolerance of ±0.1V within each bin. This helps in designing stable current-drive circuits.

3.2 Luminous Intensity (IV) Binning

The luminous output is binned using codes like Q11, Q12, R11, etc. Each bin defines a specific range of millicandela (mcd) output at 5mA (e.g., Q11: 71.0-81.0 mcd, R21: 146.0-165.0 mcd). The tolerance for luminous intensity within a bin is ±15%.

3.3 Hue (Chromaticity) Binning

The color of the white light is precisely controlled through hue bins (S1-2, S2-2, S3-1, etc.). Each bin is defined by a quadrilateral area on the CIE 1931 chromaticity diagram, specifying the allowable range of x and y coordinates. The tolerance for the chromaticity coordinates (x, y) within a bin is ±0.01. A diagram in the datasheet visually maps these bins.

4. Mechanical and Package Information

4.1 Package Dimensions

The device conforms to a specific SMD footprint. All critical dimensions are provided in millimeters, with a general tolerance of ±0.25 mm unless otherwise specified. The datasheet also includes notes on acceptable cosmetic defects, such as limits on foreign material, ink contamination, bubbles within segments, bending of the reflector, and plastic pin burrs.

4.2 Pin Configuration and Circuit Diagram

The LTD-3812SW-P is a common anode display. The internal circuit diagram shows the interconnection of the LED segments for three digits (though the device is a dual-digit display, the pinout suggests a design compatible with a triple-digit footprint). The pin connection table clearly lists the function of each of the 10 pins: for example, Pin 1 is the common anode for Digit 1, Pin 2 is the cathode for segments D2 & D3, and so on. Pin 10 is noted as \"No Connection.\"

5. Soldering and Assembly Guidelines

5.1 SMT Soldering Instructions

The device is intended for reflow soldering processes. Critical parameters are specified to prevent thermal damage.

• Reflow Process Limit: The device can withstand a maximum of two reflow soldering cycles. The assembly must be allowed to cool to normal temperature between the first and second cycle.
• Reflow Profile: Recommended pre-heat temperature is 120-150°C for a maximum of 120 seconds. The peak temperature during reflow must not exceed 260°C.
• Hand Soldering: If using a soldering iron, the tip temperature should not exceed 300°C, and contact time should be limited to 3 seconds maximum.

5.2 Recommended Soldering Pattern

A land pattern (footprint) design is provided to guide PCB layout. This includes the recommended pad geometry and a cutout area, which is crucial for proper solder joint formation and preventing solder bridging.

6. Packaging Specification

The components are supplied on tape-and-reel packaging for automated assembly. Detailed dimensions for the packing reel and the carrier tape are provided, including reel diameter, tape width, pocket spacing, and leader/trailer lengths. A diagram indicates the direction for pulling the tape during feeder setup.

7. Application Notes and Design Considerations

7.1 Typical Application Scenarios

The LTD-3812SW-P is ideal for applications requiring compact, reliable numeric displays. This includes consumer electronics (e.g., microwave ovens, air conditioners, audio equipment), industrial instrumentation (panel meters, control readouts), automotive interior displays (where temperature and other statuses are shown), and medical device interfaces.

7.2 Design Considerations

• Current Driving: Always use a constant current driver or a current-limiting resistor in series with each common anode or segment cathode. The design must respect the absolute maximum continuous current rating and implement proper derating with temperature.
• Multiplexing: As a common anode display with separate segment cathodes, it is well-suited for multiplexed drive circuits, which reduce the number of required microcontroller I/O pins.
• ESD Protection: Incorporate ESD protection diodes on PCB lines connected to the display pins, especially if the display is user-accessible.
• Thermal Management: Ensure the PCB layout provides adequate thermal relief, especially if operating near maximum ratings or in high ambient temperatures.

8. Technical Comparison and Differentiation

Compared to older technologies like red GaAsP LEDs or vacuum fluorescent displays (VFDs), the InGaN-based white LED offers superior brightness, wider viewing angles, lower power consumption, and longer lifetime. Within its category, the LTD-3812SW-P's key differentiators are its specific 0.3-inch digit height, the precise binning for intensity and color, its RoHS-compliant construction, and the detailed specification for SMT assembly compatibility.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the derating curve for forward current?
A: The derating curve (0.11 mA/°C above 25°C) is critical for reliability. As the LED's junction temperature rises, its ability to dissipate heat decreases. Derating the current prevents thermal runaway and ensures the junction temperature stays within safe limits, preserving luminous output and lifespan.

Q: Why are there bins for chromaticity?
A: The manufacturing process for white LEDs involves phosphor conversion, which can lead to slight variations in the exact shade of white. Binning groups LEDs with nearly identical color coordinates. This is essential in multi-digit or multi-device applications to avoid visually distracting color mismatches between adjacent displays or segments.

Q: Can I drive this display with a 3.3V microcontroller pin directly?
A: No. The forward voltage (VF) of the LED chips is typically 2.7-3.2V. Connecting a 3.3V supply directly to an anode (through a resistor) might barely light the LED inefficiently or not at all, depending on the actual VF. A proper driver circuit is needed to provide adequate voltage and regulate current.

10. Operational Principles

The device operates on the principle of electroluminescence in a semiconductor p-n junction. When a forward voltage exceeding the diode's threshold is applied (anode positive relative to cathode), electrons and holes recombine in the active region (InGaN quantum wells), releasing energy in the form of photons. The primary light from the InGaN chip is in the blue spectrum. A phosphor coating on the chip absorbs a portion of this blue light and re-emits it as yellow light. The mixture of the remaining blue light and the converted yellow light is perceived by the human eye as white light.