LTD-5221AJF LED Digital Tube Datasheet - 0.56 Inch Character Height - AlInGaP Yellow Orange - 2.6V Forward Voltage - Technical Documentation

1. Product Overview

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

The core advantage of this device lies in its LED chips, which utilize Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material. This material system is renowned for its high luminous efficiency and excellent color purity within the red to yellow-orange spectral range. The display features a light gray panel with white segment colors, contributing to high contrast and easy character readability under various ambient lighting conditions.

This display is classified as a low-current device, specifically tested and screened for optimal performance under low drive currents. Its design aims to deliver excellent character appearance, high brightness, and a wide viewing angle, ensuring clear visibility from multiple perspectives. The solid-state construction provides inherent reliability and a long operational life, making it suitable for applications demanding high durability.

1.1 Core Features and Target Applications

The key features defining this product include a 0.56-inch (14.22 mm) character height, achieving a good balance between size and readability. Its segment codes are continuous and uniform, presenting a clean and professional aesthetic. Its low power requirement is a significant advantage for battery-powered or energy-sensitive devices.

The device is classified by luminous intensity, meaning units are binned or screened based on their light output to ensure brightness consistency among multiple displays within a single product. This is crucial for applications such as multi-digit panel meters or scoreboards.

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

2. In-depth Analysis of Technical Parameters

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

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device and are not applicable to normal operating conditions.

• Power dissipation per segment:70 mW. This is the maximum power that a single LED segment can safely dissipate without causing overheating.
• Peak forward current per segment:90 mA. This is only allowed under pulse conditions (0.1 ms pulse width, 1/10 duty cycle), for example in multiplexed drive schemes, to achieve higher instantaneous brightness.
• Continuous forward current per segment:25 mA at 25°C. This current is linearly derated at a rate of 0.33 mA/°C when the ambient temperature exceeds 25°C. This derating is crucial for thermal management.
• Reverse voltage per segment:5 V. Exceeding this voltage under reverse bias may damage the PN junction of the LED.
• Operating and storage temperature range:-35°C to +85°C. This wide range ensures functionality in harsh environments.
• Soldering temperature:The device can withstand a peak temperature of 260°C for 3 seconds at 1/16 inch (approximately 1.6 mm) below the mounting plane.

2.2 Electrical and Optical Characteristics

These parameters describe the performance of the device under normal operating conditions.

• Average luminous intensity (Iv):At a forward current (IF) of 1 mA, the range is from 320 μcd (minimum) to 700 μcd (typical). This extremely low drive current highlights its high efficiency. Intensity measurement is performed using a filter that simulates the human eye's photopic vision response (CIE curve).
• Forward voltage (VF) per segment:The typical value is 2.6 V, with a maximum of 2.6 V at IF=20 mA. The minimum value is 2.05 V. This parameter is crucial for designing current limiting circuits.
• Peak emission wavelength (λp):611 nm. This is the wavelength at which the emission intensity is highest, defining the yellow-orange color.
• Dominant Wavelength (λd):605 nm. This is the wavelength perceived by the human eye and is closely related to the color point.
• Spectral line half-width (Δλ):17 nm. This indicates color purity; a narrower width means the color is more saturated and purer.
• Reverse current per segment (IR):At a reverse voltage (VR) of 5V, the maximum is 100 μA.
• Luminous intensity matching ratio (Iv-m):Maximum 2:1. This parameter specifies the maximum allowable ratio between the brightest and darkest segments within a single digit under the same driving conditions (IF=1mA) to ensure uniformity.

3. Grading and Classification System

The datasheet clearly states that the device is "classified by luminous intensity". This implies the existence of a grading process.

3.1 Luminous Intensity Grading

Although this document does not provide specific binning codes, the actual operation involves testing each display or each batch of LEDs and grouping them (binning) 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 of all digits in multi-digit display applications. When consistency is a key design requirement, designers must consult the manufacturer's specific binning documentation for available codes and specifications.

4. Performance Curve Analysis

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

4.1 Typical Curve Interpretation

Although no specific plots are provided in the given text, standard curves for such devices typically include:

• Forward Current vs. Forward Voltage (I-V Curve):This nonlinear 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 a constant-current driver. The "knee point" of this curve is typically around the common VF value.
• Luminous Intensity vs. Forward Current (I-L Curve):This graph shows how light output increases with drive current. It is typically linear within a certain range but may saturate at extremely high currents. The curve confirms high efficiency at low currents (as shown by the 1mA test point of Iv).
• Luminous Intensity vs. Ambient Temperature:This curve illustrates the thermal derating of light output. As temperature increases, LED efficiency decreases, leading to reduced luminous intensity at the same drive current. This reinforces the importance of current derating as specified in the Absolute Maximum Ratings.
• Spectral Distribution Curve:This graph will display the relative intensity of emitted light at different wavelengths around the 611 nm peak, with a width defined by the 17 nm FWHM parameter.

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

5. Mechanical and Packaging Information

5.1 Package Dimensions and Tolerances

The physical outline and key dimensions of the device are provided in the drawing (referenced but not shown). All dimensions are in millimeters, with a standard tolerance of ±0.25 mm (0.01 in) unless otherwise specified in feature-specific notes. This information is critical for PCB layout, ensuring proper pad and aperture design, and mechanical integration into the final product enclosure.

5.2 Pin Connections and Internal Circuitry

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

• Configuration:Common anode. This means the anodes of all LEDs for each digit are internally connected together. 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:This 18-pin device assigns specific pins to the cathodes for segments A-G and the decimal point (D.P.) of digit 1 and digit 2, as well as to two common anode pins (one for each digit). Pin 1 is marked as "No Connection" (N.C.).
• Decimal point:The datasheet specifies a "right decimal point", indicating the position of the decimal point relative to the digit.

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

6. Soldering and Assembly Guide

Absolute Maximum Ratings provide critical soldering parameters: The device can withstand a peak temperature of 260°C measured 1.6 mm below the mounting plane for 3 seconds. This aligns with typical lead-free reflow soldering temperature profiles.

6.1 Recommended Practices

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

7. Application Design Considerations

7.1 Driver Circuit Design

Proper design of the drive circuit is crucial for performance and lifespan.

• Current Limiting:It is essential to connect a current-limiting resistor in series with each common anode (for static driving) or use a constant current driver. The resistor value can be calculated using Ohm's Law: R = (Vcc - VF) / IF. For example, with Vcc at 5V, VF at 2.6V, and a desired IF of 10 mA: R = (5 - 2.6) / 0.01 = 240 Ω.
• Low Current Operation:The device's characteristic parameters are as low as 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 practice. This involves enabling the common anode of one digit at a time while presenting the segment data for that digit. The peak current rating (90 mA, 1/10 duty cycle) allows for higher pulse currents to compensate for the reduced duty cycle, thereby maintaining perceived brightness. The average current per segment must still adhere to the continuous current rating.
• Microcontroller Interface:For common anode displays, the microcontroller pins connected to the segment cathodes should be configured as outputs. To turn on a segment, set the corresponding pin low. To turn it off, set it high (or to high-impedance if possible). The common anode pin is typically driven by an external transistor (e.g., a PNP BJT or P-channel MOSFET) capable of supplying the full digit current.

7.2 Thermal Management

Although LEDs are efficient, they still generate heat. A continuous current derating factor of 0.33 mA/°C must be considered in the design. If the display is expected to operate in a high-temperature environment (e.g., inside a sealed enclosure or near other heat sources), the maximum allowable continuous current must be reduced accordingly. If driven near or at the maximum rated current, ensure adequate ventilation or heat sinking.

8. Technical Comparison and Differentiation

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

• Comparison with 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.
• Compared to standard brightness LEDs:This device is specifically "tested and screened" for low-current performance. Many standard seven-segment displays are characterized at 20mA; this device guarantees performance at 1mA, making it superior for battery-critical applications.
• Compared to blue/green/white LED displays:Yellow-orange (605-611 nm) offers excellent visibility and is generally considered less straining on the eyes under low-light conditions compared to shorter wavelength colors. It also typically provides higher luminous efficiency than earlier 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 using 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 will cause excessive current to flow, potentially damaging 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 emission spectrum. Dominant wavelength (λd=605nm) is the wavelength of a pure monochromatic light that appears to an observer to have the same color as the LED. They are typically close but not identical.

Q: The matching ratio is 2:1. Does this mean one segment could be up to twice as bright as another?
A: Yes, this specification allows for that maximum difference under identical test conditions. For most applications, this difference is not perceptually significant. If extremely high 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 for outdoor applications?
A: The operating temperature range (-35°C to +85°C) supports many outdoor environments. However, direct exposure to sunlight and weather requires conformal coating for the PCB and a protective window for the display to prevent plastic UV aging and moisture ingress. The high contrast of the light gray/white panel aids readability in sunlight.

10. Practical Design and Usage Examples

10.1 Case Study: Portable Multimeter Display

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

10.2 Case Study: Industrial Timer/Counter

For panel-mounted industrial timers, reliability and visibility are key. The solid-state reliability of LED displays surpasses older technologies like Vacuum Fluorescent Displays (VFD) in terms of shock/vibration resistance and lifespan. The stability of the AlInGaP material ensures that the display color and brightness do not shift significantly over years of continuous operation. The common anode configuration simplifies interfacing with industrial PLC digital output modules, which typically use a common ground scheme.

11. Introduction to Technical Principles

The LTD-5221AJF is based on Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor technology grown on an opaque Gallium Arsenide (GaAs) substrate. This material system allows for precise design 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 photon emission in the yellow-orange region (approximately 611 nm) when electrons recombine with holes across the PN junction under forward bias.

The "opaque GaAs substrate" is significant. Early red LEDs used transparent GaP substrates, but AlInGaP layers have better lattice matching with GaAs. The substrate itself absorbs some of the generated light, but in high-end devices, modern chip designs employ techniques such as Distributed Bragg Reflectors (DBR) or wafer bonding to transparent substrates (like GaP) to improve light extraction efficiency. This datasheet mentioning an opaque substrate indicates a standard, cost-effective chip design.

12. Technical Trends and Background

Although 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 field has evolved.

• Trend of Integration:Modern applications typically use dot-matrix OLED or LCD displays for greater flexibility in displaying text and graphics. However, for simple, high-brightness, low-cost numeric readout applications that do not require customization, seven-segment LEDs remain unmatched.
• Efficiency Improvement:Ongoing research on AlInGaP materials and chip designs (such as thin-film flip-chip designs) continuously drives improvements in luminous efficacy (lumens per watt), enabling brighter displays at lower currents or reduced heat generation.
• Color Mixing:For full-color applications, red AlInGaP LEDs are used in combination with indium gallium nitride (InGaN) blue and green LEDs. Yellow-orange variants like the LTD-5221AJF find their place in monochrome applications where their specific color and high efficiency are favored.
• Driver Integration:A modern trend is to integrate the LED display with the driver IC in a single package or module, simplifying design and reducing component count, although the unit cost may be higher.

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