LTC-4624JR LED Display Datasheet - 0.4-inch Digit Height - Super Red (631nm) - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTC-4624JR is a compact, high-performance, triple-digit, seven-segment LED display module. Its primary application is in electronic equipment requiring clear, bright numeric readouts, such as test instruments, industrial control panels, point-of-sale terminals, and consumer appliances. The core advantage of this device lies in its use of AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the LED chips, which provides superior luminous efficiency and color purity in the red spectrum compared to older technologies like GaAsP. This results in excellent character appearance with high brightness and contrast, making the digits easily readable even under various ambient lighting conditions. The device is categorized for luminous intensity, allowing for consistent brightness matching in multi-display applications.

1.1 Key Features and Device Description

The display boasts several notable features that contribute to its reliability and performance. It has a 0.4-inch (10.0mm) digit height, providing a good balance between size and readability. The segments are continuous and uniform, ensuring a clean and professional appearance. It operates with a low power requirement, enhancing energy efficiency. The solid-state construction offers high reliability and long operational life. Furthermore, the package is lead-free, complying with RoHS (Restriction of Hazardous Substances) directives, making it suitable for modern electronic manufacturing.

The specific part number, LTC-4624JR, denotes a device with AlInGaP Super Red LED chips arranged in a multiplex common cathode configuration. It includes a right-hand decimal point for each digit. The visual design features a gray face with white segments, which maximizes contrast and improves readability.

2. Technical Parameters: In-Depth Objective Interpretation

2.1 Absolute Maximum Ratings

Understanding the absolute maximum ratings is crucial for ensuring the long-term reliability of the display. These ratings define the limits beyond which permanent damage may occur. The power dissipation per segment is rated at 70 mW. The peak forward current per segment is 90 mA, but this is only permissible under specific pulsed conditions: a 1/10 duty cycle and a 0.1ms pulse width. The continuous forward current per segment is 25 mA at 25°C, and it derates linearly at a rate of 0.33 mA/°C as the ambient temperature increases. This derating is essential for thermal management. The device is rated for an operating and storage temperature range of -35°C to +85°C. The solder reflow condition is specified as 260°C for 3 seconds at a distance of 1/16 inch (approximately 1.6mm) below the seating plane of the component on the PCB.

2.2 Electrical and Optical Characteristics

The electrical and optical characteristics are measured at a standard ambient temperature of 25°C. The average luminous intensity (Iv) ranges from a minimum of 200 µcd to a typical 650 µcd at a forward current (IF) of 1 mA. The peak emission wavelength (λp) is typically 639 nm, and the dominant wavelength (λd) is 631 nm at IF=20mA, placing it firmly in the super red color region. The spectral line half-width (Δλ) is 20 nm, indicating a relatively pure color. The forward voltage (VF) per LED chip is between 2.0V (min) and 2.6V (max) at 20mA. The reverse current (IR) per segment has a maximum of 100 µA at a reverse voltage (VR) of 5V. It is critically important to note that this reverse voltage rating is for test purposes only; continuous operation under reverse bias must be avoided in the application circuit. The luminous intensity matching ratio between segments in a similar light area is 2:1 maximum, ensuring visual uniformity. Additional notes specify that cross-talk between segments should be ≤2.5% and the forward voltage tolerance is ±0.1V.

3. Mechanical and Package Information

The display is provided in a standard through-hole DIP (Dual In-line Package) format. The package dimensions are detailed in the datasheet with all measurements in millimeters. Key tolerances include ±0.25mm for most dimensions and a pin tip shift tolerance of ±0.4mm. Quality control notes specify limits for foreign material on segments (≤10mil), bending of the reflector (≤1% of length), bubbles in segments (≤10mil), and ink contamination on the surface (≤20mil). For PCB design, a hole diameter of 1.0mm is recommended for the leads.

3.1 Pin Connection and Internal Circuit

The device has a 14-pin configuration, though not all positions are populated. It utilizes a multiplex common cathode architecture. The internal circuit diagram shows that each of the three digits shares its anode connection (common anode for digit 1, 2, and 3 on pins 1, 5, and 7 respectively). The segment cathodes (A-G and DP) are connected across digits. Additionally, there are separate cathodes for the right-side LEDs (L1, L2, L3) which share a common anode on pin 14. This multiplexing scheme reduces the number of required driver pins from 24 (3 digits * 8 segments) to 14, simplifying the interfacing circuitry. The pinout is as follows: Pin 1: Common Anode Digit 1; Pin 2: Cathode E; Pin 3: Cathode C, L3; Pin 4: Cathode D; Pin 5: Common Anode Digit 2; Pin 6: Cathode DP; Pin 7: Common Anode Digit 3; Pin 8: Cathode G; Pins 9,10,13: No Connection; Pin 11: Cathode B, L2; Pin 12: Cathode A, L1; Pin 14: Common Anode L1,L2,L3; Pin 15: Cathode F.

4. Application Guidelines and Design Considerations

4.1 Driving and Circuit Design

For optimal performance and longevity, several application cautions must be heeded. The display is intended for ordinary electronic equipment. Using a constant current drive method is strongly recommended over constant voltage driving. This ensures consistent luminous output regardless of variations in the forward voltage (VF) of individual LED chips within the display. The driving circuit must be designed to accommodate the full range of VF (2.0V to 2.6V) to guarantee the intended drive current is always delivered. The circuit must also incorporate protection against reverse voltages and transient voltage spikes during power-up or shutdown, as reverse bias can cause metal migration and lead to increased leakage or short circuits. The safe operating current should be derated based on the maximum expected ambient temperature in the end application, using the 0.33 mA/°C derating factor from the absolute maximum ratings.

4.2 Thermal and Environmental Considerations

Exceeding the recommended operating current or temperature can lead to severe light output degradation or premature failure. Designers must ensure adequate heat dissipation in the application. Rapid changes in ambient temperature, especially in high-humidity environments, should be avoided as they can cause condensation on the display, potentially leading to electrical or optical issues. Mechanical stress on the display body should be avoided during assembly; unsuitable tools or methods must not be used.

4.3 Assembly and Interfacing Notes

If a decorative film or overlay is used, it is typically attached with pressure-sensitive adhesive. It is not recommended to let this film side be in close contact with a front panel or cover, as external force may cause it to shift. For applications using two or more displays in one set, it is recommended to use displays from the same luminous intensity BIN code to avoid noticeable differences in brightness (hue unevenness). If the end product requires the display to undergo drop or vibration testing, the specific test conditions should be evaluated in advance.

5. Storage and Handling

Proper storage is essential to maintain solderability and performance. The recommended storage conditions for the LED display in its original packaging are a temperature between 5°C and 30°C and a relative humidity below 60% RH. Storage outside these conditions may lead to oxidation of the component leads. It is advised to consume inventory promptly and avoid long-term storage of large quantities. If the moisture barrier bag has been opened for more than six months, a baking process of 60°C for 48 hours is recommended prior to assembly, with assembly to be completed within one week after baking.

6. Performance Curves and Binning System

The datasheet references typical electrical/optical characteristic curves, which would normally illustrate the relationship between forward current (IF) and luminous intensity (Iv), forward voltage (VF) vs. temperature, and the spectral distribution. These curves are vital for designers to predict performance under non-standard conditions. The device is categorized (binned) for luminous intensity. This means units are tested and grouped based on their measured light output at a standard test current. Using displays from the same bin in a multi-unit application ensures visual consistency. While the PDF excerpt does not detail wavelength or voltage binning, the tight specifications on dominant wavelength (631nm) and forward voltage tolerance (±0.1V) inherently provide a high degree of uniformity.

7. Technical Comparison and Differentiation

The primary differentiation of the LTC-4624JR lies in its use of AlInGaP technology for the red LEDs. Compared to older GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current, or equivalent brightness at lower power. It also provides a more saturated and pure red color (dominant wavelength ~631nm) compared to the often orangey-red hue of GaAsP. The multiplex common cathode design offers a pin-efficient interface compared to static drive displays, reducing microcontroller I/O or driver IC requirements. The gray face with white segments is a design choice that enhances contrast, making it preferable over all-red or low-contrast color schemes in many applications.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the \"L1, L2, L3\" pins mentioned in the pinout?
A: These are cathode pins for additional LEDs, likely positioned on the right side of each digit (e.g., for a colon in a clock display or other indicators). They share a common anode on pin 14 and can be controlled independently of the seven-segment digits.

Q: Can I drive this display with a 5V microcontroller using current-limiting resistors?
A: Yes, but careful calculation is needed. Assuming a VF of 2.6V (max) and a desired IF of 20mA, the required series resistor would be R = (5V - 2.6V) / 0.02A = 120 Ohms. You must ensure the microcontroller pin can sink or source the required multiplexed current. A dedicated driver IC (like a MAX7219 or HT16K33) is often a more robust solution.

Q: The absolute max continuous current is 25mA at 25°C but derates. What current should I use for reliable operation at 50°C?
A: Using the derating factor of 0.33 mA/°C: Temperature rise = 50°C - 25°C = 25°C. Current derating = 25°C * 0.33 mA/°C = 8.25 mA. Therefore, the maximum recommended continuous current at 50°C is 25 mA - 8.25 mA = 16.75 mA. Operating at or below this current ensures reliability.

Q: Why is reverse bias so strongly cautioned against?
A: Applying a reverse voltage (even the 5V used for the IR test) can cause electromigration of metal atoms within the semiconductor junction. Over time, this can create conductive paths, leading to increased leakage current or a permanent short circuit, rendering the segment inoperative.

9. Operating Principle

A seven-segment display is an assembly of seven LED bars (segments A through G) arranged in a figure-\"8\" pattern, plus an additional LED for a decimal point (DP). By selectively illuminating specific combinations of these segments, all decimal digits (0-9) and some letters can be formed. The LTC-4624JR integrates three such digit assemblies into one package. It uses a multiplexed common cathode design. In this scheme, all the anodes for the same segment across different digits are connected together internally. The cathodes for each digit are separate. To display a number, the microcontroller activates (drives high) the anodes for the segments that should be lit for the desired character on all digits. It then grounds (drives low) the cathode of the specific digit where that character should appear. This process is repeated rapidly for each digit (typically at a frequency >100Hz). Due to persistence of vision, all three digits appear to be lit simultaneously and continuously. This method drastically reduces the number of required control lines compared to individually wiring each of the 24 segments (3 digits * 8 segments).

10. Development Trends and Context

The LTC-4624JR represents a mature and reliable technology for through-hole numeric displays. The broader trend in display technology is moving towards surface-mount device (SMD) packages for automated assembly, higher density, and thinner profiles. For seven-segment displays, this means packages like SMD LEDs on a flexible PCB or chip-on-board (COB) designs. There is also a continuous drive towards higher efficiency LED materials, with AlInGaP being a standard for red/orange/yellow and InGaN for blue/green/white. While OLEDs and dot-matrix LCDs offer more graphical flexibility, seven-segment LED displays remain dominant in applications where high brightness, wide viewing angles, extreme temperature tolerance, and simple digital readouts are paramount, such as in industrial, automotive, and outdoor equipment. The principles of multiplexing and constant-current drive discussed for this device remain foundational for interfacing with most modern multi-digit LED displays, regardless of package type.