LTD-5221AJF LED Display Datasheet - 0.56-inch Digit Height - AlInGaP Yellow Orange - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTD-5221AJF is a high-performance, seven-segment alphanumeric display module designed for applications requiring clear, bright numeric readouts with low power consumption. Its primary function is to provide a highly legible display for digital instruments, consumer electronics, and industrial control panels.

The core advantage of this device lies in its utilization of Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor material for the LED chips. This material system is renowned for its high luminous efficiency and excellent color purity in the red to yellow-orange spectrum. The display features a light gray face and white segment color, which contributes to a high contrast ratio, making the characters easily readable even under various ambient lighting conditions.

This display is categorized as a low-current device, specifically tested and selected for optimal performance at low drive currents. It is engineered to deliver excellent character appearance, high brightness, and a wide viewing angle, ensuring visibility from multiple perspectives. The solid-state construction offers inherent reliability and long operational life, making it suitable for applications where durability is critical.

1.1 Core Features and Target Applications

The key features that define this product include a 0.56-inch (14.22 mm) digit height, which offers a good balance between size and readability. The segments are continuous and uniform, providing a clean and professional aesthetic. Its low power requirement is a significant benefit for battery-operated or energy-sensitive devices.

The device is categorized for luminous intensity, meaning units are binned or sorted based on their light output, allowing for consistency in brightness across multiple displays in a single product. This is crucial for applications like multi-digit panel meters or scoreboards.

Typical target markets and applications include portable test equipment, medical devices, automotive dashboards (for auxiliary displays), home appliance controls, point-of-sale terminals, and industrial timer/counter displays. Its reliability and performance make it a preferred choice for both consumer and professional-grade electronics.

2. Technical Parameter Deep-Dive Analysis

The electrical and optical characteristics of the LTD-5221AJF are specified under standard test conditions at an ambient temperature (TA) of 25°C. A detailed understanding of these parameters is essential for proper circuit design and ensuring long-term reliability.

2.1 Absolute Maximum Ratings

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

• Power Dissipation per Segment: 70 mW. This is the maximum power that can be safely dissipated by a single LED segment without causing overheating.
• Peak Forward Current per Segment: 90 mA. This is allowed only under pulsed conditions (0.1ms pulse width, 1/10 duty cycle), such as in multiplexed driving schemes, to achieve higher instantaneous brightness.
• Continuous Forward Current per Segment: 25 mA at 25°C. This current derates linearly at a rate of 0.33 mA/°C as the ambient temperature rises above 25°C. This derating is crucial for thermal management.
• Reverse Voltage per Segment: 5 V. Exceeding this voltage in reverse bias can damage the LED's PN junction.
• Operating & Storage Temperature Range: -35°C to +85°C. This wide range ensures functionality in harsh environments.
• Solder Temperature: The device can withstand a soldering temperature of 260°C for 3 seconds at a point 1/16 inch (approx. 1.6mm) below the seating plane.

2.2 Electrical & Optical Characteristics

These parameters describe the device's performance under normal operating conditions.

• Average Luminous Intensity (Iv): Ranges from 320 μcd (min) to 700 μcd (typical) at a forward current (IF) of 1 mA. This exceptionally low drive current highlights its efficiency. The intensity is measured using a filter that mimics the human eye's photopic response (CIE curve).
• Forward Voltage per Segment (VF): Typically 2.6 V, with a maximum of 2.6 V at IF=20 mA. The minimum is 2.05 V. This parameter is vital for designing the current-limiting circuitry.
• Peak Emission Wavelength (λp): 611 nm. This is the wavelength at which the emitted light intensity is highest, defining the yellow-orange color.
• Dominant Wavelength (λd): 605 nm. This is the wavelength perceived by the human eye, closely related to the color point.
• Spectral Line Half-Width (Δλ): 17 nm. This indicates the color purity; a narrower width means a more saturated, pure color.
• Reverse Current per Segment (IR): Maximum 100 μA at a reverse voltage (VR) of 5V.
• Luminous Intensity Matching Ratio (Iv-m): 2:1 maximum. This specifies the maximum allowable ratio between the brightest and dimmest segments within a single digit when driven under the same conditions (IF=1mA), ensuring uniformity.

3. Binning and Categorization System

The datasheet explicitly states that the device is \"categorized for luminous intensity.\" This implies a binning process.

3.1 Luminous Intensity Binning

While specific bin codes are not provided in this document, the practice involves testing each display or batch of LEDs and sorting them into groups (bins) based on their measured light output at a standard test current (e.g., 1mA or 20mA). This allows manufacturers to purchase displays with a guaranteed minimum brightness or within a specific brightness range, ensuring visual consistency across all digits in a multi-digit display application. Designers must consult the manufacturer's specific binning documentation for available codes and specifications when consistency is a critical design requirement.

4. Performance Curve Analysis

The datasheet references \"typical electrical/optical characteristic curves,\" which are essential tools for understanding device behavior beyond the single-point data in the tables.

4.1 Interpretation of Typical Curves

Although the specific graphs are not rendered in the provided text, standard curves for such devices would typically include:

• Forward Current vs. Forward Voltage (I-V Curve): This non-linear curve shows the relationship between the voltage across the LED and the current flowing through it. It is crucial for selecting the appropriate current-limiting resistor or designing constant-current drivers. The \"knee\" of this curve is around the typical VF value.
• Luminous Intensity vs. Forward Current (I-L Curve): This graph shows how light output increases with drive current. It is generally linear over a range but may saturate at very high currents. The curve confirms the high efficiency at low currents (as evidenced by the 1mA test point for Iv).
• Luminous Intensity vs. Ambient Temperature: This curve demonstrates the thermal derating of light output. As temperature increases, the efficiency of the LED decreases, leading to lower luminous intensity for the same drive current. This reinforces the importance of the current derating specified in the absolute maximum ratings.
• Spectral Distribution Curve: This plot would show the relative intensity of light emitted across different wavelengths, centered around the 611 nm peak, with the width defined by the 17 nm half-width parameter.

Designers should use these curves to predict performance under non-standard conditions, such as different drive currents or operating temperatures.

5. Mechanical and Package Information

5.1 Package Dimensions and Tolerances

The device's physical outline and critical dimensions are provided in a drawing (referenced but not shown). All dimensions are in millimeters, with a standard tolerance of ±0.25 mm (0.01 inch) unless a specific feature note states otherwise. This information is critical for PCB layout, ensuring the footprint and cutouts are correctly designed, and for mechanical integration into the final product enclosure.

5.2 Pin Connection and Internal Circuit

The LTD-5221AJF is a two-digit, common anode display. The internal circuit diagram and pin connection table are essential for correct wiring.

• Configuration: Common Anode. This means the anodes of all LEDs for each digit are connected together internally. To illuminate a segment, its corresponding cathode pin must be driven low (connected to ground or a current sink) while the common anode for that digit is driven high (connected to VCC through a current-limiting resistor).
• Pinout: The 18-pin device has a specific assignment for the cathodes of segments A-G and the decimal point (D.P.) for both Digit 1 and Digit 2, along with the two common anode pins (one per digit). Pin 1 is marked as \"No Connection\" (N.C.).
• Decimal Point: The datasheet specifies \"Rt. Hand Decimal,\" indicating the position of the decimal point relative to the digits.

This common anode configuration is often preferred in microcontroller-based systems where I/O pins are better at sinking current (driving low) than sourcing it (driving high).

6. Soldering and Assembly Guidelines

The absolute maximum ratings provide the key soldering parameter: the device can withstand a peak temperature of 260°C for 3 seconds, measured 1.6mm below the seating plane. This aligns with typical lead-free reflow soldering profiles.

6.1 Recommended Practices

• Reflow Soldering: Use a standard lead-free reflow profile with a peak temperature not exceeding 260°C. The time above liquidus (e.g., 217°C) should be controlled to minimize thermal stress on the plastic package and internal wire bonds.
• Hand Soldering: If hand soldering is necessary, use a temperature-controlled iron. Apply heat to the PCB pad, not directly to the display pin, and limit contact time to prevent overheating.
• Cleaning: Use cleaning solvents that are compatible with the display's plastic material to avoid discoloration or degradation.
• Storage: Store in a dry, anti-static environment within the specified temperature range (-35°C to +85°C) to prevent moisture absorption (which can cause \"popcorning\" during reflow) and electrostatic discharge damage.

7. Application Design Considerations

7.1 Driving Circuit Design

Designing the drive circuitry correctly is paramount for performance and longevity.

• Current Limiting: ALWAYS use a current-limiting resistor in series with each common anode (for static drive) or use a constant-current driver. The resistor value can be calculated using Ohm's Law: R = (Vcc - VF) / IF. For example, with a Vcc of 5V, a VF of 2.6V, and a desired IF of 10 mA: R = (5 - 2.6) / 0.01 = 240 Ω.
• Low-Current Operation: The device is characterized down to 1mA per segment. For ultra-low-power applications, driving at 1-2 mA can provide sufficient visibility while minimizing power consumption.
• Multiplexing: For multi-digit displays, multiplexing is standard. This involves sequentially enabling one digit's common anode at a time while presenting the segment data for that digit. The peak current rating (90 mA at 1/10 duty cycle) allows for higher pulsed currents to compensate for the reduced duty cycle, maintaining perceived brightness. The average current per segment must still respect the continuous current rating.
• Microcontroller Interface: For common anode displays, the microcontroller pins connected to segment cathodes should be configured as outputs. To turn a segment ON, set the corresponding pin to LOW. To turn it OFF, set it to HIGH (or high-impedance if possible). The common anode pins are typically driven by external transistors (e.g., PNP BJTs or P-channel MOSFETs) capable of sourcing the total digit current.

7.2 Thermal Management

While LEDs are efficient, they still generate heat. The 0.33 mA/°C derating factor for continuous current must be considered in the design. If the display is expected to operate in a high ambient temperature environment (e.g., inside a sealed enclosure or near other heat sources), the maximum allowable continuous current must be reduced accordingly. Ensure adequate ventilation or heatsinking if driving at or near the maximum rated current.

8. Technical Comparison and Differentiation

The LTD-5221AJF's primary differentiation lies in its material technology and low-current optimization.

• vs. Traditional GaAsP or GaP LEDs: AlInGaP technology offers significantly higher luminous efficiency and better temperature stability, resulting in brighter displays with more consistent color over temperature and lifetime.
• vs. Standard Brightness LEDs: This device is specifically \"tested and selected\" for low-current performance. Many standard seven-segment displays are characterized at 20mA; this one guarantees performance at 1mA, making it superior for battery-critical applications.
• vs. Blue/Green/White LED Displays: The yellow-orange color (605-611 nm) offers excellent visibility and is often considered less straining on the eyes in low-light conditions compared to shorter wavelength colors. It also typically has a higher luminous efficacy than early blue or white LEDs.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display directly from a 3.3V microcontroller pin without a current-limiting resistor?
A: No. You must always use a current-limiting mechanism (resistor or constant-current driver). Even if Vcc (3.3V) is close to VF (2.05-2.6V), the lack of a resistor would allow excessive current to flow, potentially damaging both the LED and the microcontroller pin.

Q: What is the difference between \"Peak Emission Wavelength\" and \"Dominant Wavelength\"?
A: Peak wavelength (λp=611nm) is the physical peak of the emitted light spectrum. Dominant wavelength (λd=605nm) is the wavelength of a pure monochromatic light that would appear to have the same color as the LED to a human observer. They are often close but not identical.

Q: The matching ratio is 2:1. Does this mean one segment could be twice as bright as another?
A: Yes, the specification allows for this maximum variation under identical test conditions. For most applications, this variation is not perceptibly objectionable. If extreme uniformity is required, consult the manufacturer for tighter binning options or consider using displays from the same production lot.

Q: Can I use this display in an outdoor application?
A: The operating temperature range (-35°C to +85°C) supports many outdoor environments. However, direct exposure to sunlight and weather requires conformal coating on the PCB and a protective window over the display to prevent UV degradation of the plastic and moisture ingress. The high contrast of the light gray/white face helps with sunlight readability.

10. Practical Design and Usage Examples

10.1 Case Study: Portable Multimeter Display

In a handheld digital multimeter, power efficiency is critical. The LTD-5221AJF can be driven at 1-2 mA per segment in a multiplexed configuration. A microcontroller with integrated LED driver segments can control 2-4 digits efficiently. The wide viewing angle allows the user to read measurements from various angles, and the high contrast ensures readability in both dim lab settings and brighter environments. The low forward voltage also helps maximize battery life when using a 3V or 4.5V battery supply.

10.2 Case Study: Industrial Timer/Counter

For a panel-mounted industrial timer, reliability and visibility are key. The solid-state reliability of the LED display surpasses older technologies like vacuum fluorescent displays (VFDs) in terms of shock/vibration resistance and lifetime. The AlInGaP material's stability ensures the display color and brightness do not shift significantly over years of continuous operation. The common anode configuration simplifies interface with industrial PLC digital output modules that often have common grounding schemes.

11. Technology Principle Introduction

The LTD-5221AJF is based on Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor technology grown on a non-transparent Gallium Arsenide (GaAs) substrate. This material system allows for the precise engineering of the semiconductor's bandgap by adjusting the ratios of Al, In, Ga, and P. A larger bandgap corresponds to shorter wavelength (higher energy) light emission. The composition used here creates a bandgap that results in the emission of photons in the yellow-orange region (around 611 nm) when electrons recombine with holes across the PN junction under forward bias.

The \"non-transparent GaAs substrate\" is significant. Early red LEDs used a transparent GaP substrate, but AlInGaP layers are lattice-matched better to GaAs. The substrate itself absorbs some of the generated light, but modern chip designs use techniques like distributed Bragg reflectors (DBRs) or wafer bonding to transparent substrates (like GaP) in higher-end devices to improve light extraction efficiency. The fact that this datasheet mentions a non-transparent substrate indicates a standard, cost-effective chip design.

12. Technology Trends and Context

While this specific datasheet is from 2000, the underlying AlInGaP technology remains highly relevant for red, orange, and yellow LEDs due to its efficiency and color stability. However, the broader display landscape has evolved.

• Trend towards Integration: Modern applications often use dot-matrix OLED or LCD displays for greater flexibility in showing text and graphics. However, seven-segment LEDs remain unbeaten for simple, high-brightness, low-cost numeric readouts where customization is not needed.
• Efficiency Improvements: Ongoing research in AlInGaP materials and chip design (like thin-film flip-chip designs) continues to push the luminous efficacy (lumens per watt) higher, allowing for even brighter displays at lower currents or reduced heat generation.
• Color Mixing: For full-color applications, red AlInGaP LEDs are combined with Indium Gallium Nitride (InGaN) blue and green LEDs. The yellow-orange variant like the LTD-5221AJF finds its niche in monochromatic applications where its specific color and high efficiency are desired.
• Driver Integration: A modern trend is the integration of the LED display with the driver IC in a single package or module, simplifying design and reducing component count, though potentially at a higher unit cost.

In summary, the LTD-5221AJF represents a mature, optimized solution for a specific and enduring application need: reliable, bright, low-power numeric display.