LTC-4624JF LED Display Datasheet - 0.4-inch Digit Height - AlInGaP Yellow Orange - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-4624JF is a high-performance, triple-digit, seven-segment LED display module designed for applications requiring clear numeric readouts. Its primary function is to visually represent numerical data with high clarity and reliability. The core advantage of this device lies in its use of advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the LED chips, which provides superior luminous efficiency and color purity compared to older technologies like standard GaAsP. The target market includes industrial instrumentation, test and measurement equipment, point-of-sale systems, automotive dashboards (for aftermarket or secondary displays), and any embedded system where a compact, bright, and easy-to-interface numeric display is required.

2. Technical Specifications Deep Dive

2.1 Photometric and Optical Characteristics

The optical performance is central to the display's functionality. The device utilizes AlInGaP chips on a non-transparent GaAs substrate, emitting in the yellow-orange spectrum. The Average Luminous Intensity (Iv) is specified from a minimum of 200 µcd to a typical value of 650 µcd at a standard test current of 1mA. This high brightness, combined with a gray face and white segments, ensures excellent contrast and character appearance. The Peak Emission Wavelength (λp) is typically 611 nm, with a Dominant Wavelength (λd) of 605 nm, firmly placing the output in the yellow-orange region. The Spectral Line Half-Width (Δλ) is approximately 17 nm, indicating a relatively pure color emission. A Luminous Intensity Matching Ratio of 2:1 (max) ensures reasonable uniformity in segment brightness across the display.

2.2 Electrical Parameters

The electrical specifications define the operating boundaries and conditions for reliable use. The Forward Voltage per Segment (VF) has a typical value of 2.6V at a forward current (IF) of 20mA, with a maximum of 2.6V. The Reverse Voltage per Segment is rated at a maximum of 5V. The Continuous Forward Current per Segment is 25 mA at 25°C, with a derating factor of 0.33 mA/°C for ambient temperatures above 25°C. For pulsed operation, a Peak Forward Current of 90 mA is allowed under specific conditions (1/10 duty cycle, 0.1ms pulse width). The Reverse Current per Segment (IR) is a maximum of 100 µA at the full reverse voltage of 5V.

2.3 Thermal and Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. The Power Dissipation per Segment must not exceed 70 mW. The device is rated for an Operating Temperature Range of -35°C to +85°C, with an identical Storage Temperature Range. For assembly, the maximum Solder Temperature is 260°C for a maximum duration of 3 seconds, measured 1.6mm below the seating plane of the component. Adhering to these limits is crucial for long-term reliability.

3. Binning and Categorization System

The datasheet explicitly states that the device is Categorized for Luminous Intensity. This means the LEDs are sorted (binned) based on their measured light output at a standard test condition (likely IF=1mA). This allows designers to select parts with consistent brightness levels for their application, preventing noticeable variations in display intensity between different units or production batches. While the document does not detail specific bin codes, the practice ensures a minimum luminous intensity of 200 µcd is met.

4. Performance Curve Analysis

The datasheet includes a section for Typical Electrical / Optical Characteristic Curves. Although the specific curves are not detailed in the provided text, such graphs typically illustrate the relationship between forward current (IF) and forward voltage (VF), the relationship between luminous intensity (Iv) and forward current (IF), and how luminous intensity varies with ambient temperature. These curves are invaluable for designers to optimize drive current for desired brightness while managing power dissipation and understanding performance under non-standard temperature conditions.

5. Mechanical and Package Information

5.1 Physical Dimensions

The device features a digit height of 0.4 inches (10.0 mm). The package dimensions are provided in a detailed drawing with all measurements in millimeters. Tolerances are generally ±0.25 mm unless otherwise specified. This information is critical for PCB footprint design and ensuring proper fit within the end product's enclosure.

5.2 Pinout and Connection Diagram

The LTC-4624JF is a multiplex common anode display. It has 15 pins, though not all are used. The internal circuit diagram and pin connection table show how the three common anode pins (for Digit 1, Digit 2, and Digit 3) and the 14 segment cathodes (A, B, C, D, E, F, G, DP, and three separate LEDs L1, L2, L3) are arranged. A dedicated common anode pin (pin 14) exists for the separate LEDs (L1, L2, L3). This multiplexed design allows control of 3 digits and additional indicators with a reduced number of microcontroller I/O pins.

6. Soldering and Assembly Guidelines

The key guideline provided is the soldering temperature limit: a maximum of 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane. This is a standard reflow soldering parameter. It is crucial to follow the recommended reflow profile for lead-free soldering processes to prevent thermal damage to the LED chips or the plastic package. The device should be stored within its specified temperature range (-35°C to +85°C) in a dry environment prior to use.

7. Application Suggestions

7.1 Typical Application Circuits

As a common anode, multiplexed display, it requires an external driver circuit. Typically, the common anode pins are connected to the collector (or drain) of PNP transistors (or P-channel MOSFETs) which are switched by a microcontroller. The segment cathode pins are connected to current-limiting resistors and then to the outputs of a sink-driver IC (like a 74HC595 shift register or a dedicated LED driver) or directly to microcontroller pins with sufficient current sink capability. The multiplexing is achieved by sequentially enabling one digit's common anode at a time while presenting the segment data for that digit, cycling through all digits rapidly enough to create a persistent image (typically >60 Hz).

7.2 Design Considerations

• Current Limiting: Essential to prevent exceeding the maximum continuous forward current (25mA/segment). Resistors must be calculated based on the supply voltage, LED forward voltage (VF), and desired current.
• Multiplexing Frequency: Must be high enough to avoid visible flicker. A refresh rate of 100-200 Hz per digit is common.
• Peak Current: In a multiplexed setup, the instantaneous current per segment during its brief on-time will be higher than the average current. Ensure the peak current does not exceed the 90mA rating for the chosen duty cycle.
• Viewing Angle: The wide viewing angle is beneficial for applications where the display may be viewed from off-center positions.
• ESD Protection: LEDs are sensitive to electrostatic discharge. Handle with appropriate ESD precautions during assembly.

8. Technical Comparison and Differentiation

The primary differentiator of the LTC-4624JF is its use of AlInGaP technology. Compared to traditional red GaAsP LEDs, AlInGaP offers significantly higher luminous efficiency, meaning brighter output for the same drive current, or the same brightness at lower power. It also provides better color saturation and stability over temperature and lifetime. The gray face/white segment design enhances contrast. Its 0.4-inch digit height offers a good balance between size and readability, fitting between smaller 0.3-inch and larger 0.5 or 0.56-inch displays.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the separate LEDs L1, L2, L3?
A: These are individual LED indicators, separate from the seven-segment digits. They can be used for status indicators, colons in a clock display, or other symbolic functions, providing additional functionality beyond just numbers.

Q: How do I calculate the current-limiting resistor value?
A: Use Ohm's Law: R = (V_supply - VF) / I_desired. For a 5V supply, a VF of 2.6V, and a desired current of 15mA: R = (5 - 2.6) / 0.015 = 160 Ohms. Use the nearest standard value (e.g., 150 or 180 Ohms).

Q: Can I drive this display without multiplexing?
A: Technically yes, by connecting all common anodes together and driving each segment cathode independently. However, this would require 11 drive lines (8 segments + DP + 3 LEDs) instead of the multiplexed scheme's reduced count, making it inefficient for microcontroller pin usage.

Q: What does \"categorized for luminous intensity\" mean for my design?
A: It ensures brightness consistency. For critical applications where uniform appearance is vital, you may specify a tighter bin code from the manufacturer if available. For most applications, the standard categorization is sufficient.

10. Practical Design and Usage Case

Case: Designing a Simple 3-Digit Voltmeter Readout. A microcontroller with an ADC measures a voltage. The firmware converts the reading to three BCD digits. A timer interrupt triggers a multiplexing routine at 150 Hz. The routine: 1) Turns off all digit anode drivers. 2) Outputs the segment pattern for Digit 1 to the cathode driver IC. 3) Enables the transistor for Digit 1's anode. 4) Waits a short time. 5) Repeats for Digits 2 and 3. The separate LEDs (L1, L2, L3) could be used to indicate measurement range (e.g., mV, V, Auto-range). The high brightness and contrast ensure readability under various lighting conditions in a lab or field setting.

11. Technology Principle Introduction

The core technology is the AlInGaP LED. AlInGaP is a III-V semiconductor compound where Aluminum, Indium, Gallium, and Phosphorus are combined in specific ratios to create a direct bandgap material that emits light in the red to yellow-green spectrum. The \"non-transparent GaAs substrate\" mentioned means the growth substrate absorbs some of the generated light, but the AlInGaP active layer itself is highly efficient. When a forward voltage is applied across the p-n junction, electrons and holes recombine, releasing energy in the form of photons. The specific composition determines the wavelength (color) of the emitted light, which in this case is yellow-orange.

12. Technology Trends and Context

While newer display technologies like OLED and high-resolution LCDs dominate consumer electronics, seven-segment LED displays remain highly relevant in industrial, commercial, and embedded contexts due to their extreme simplicity, robustness, high brightness, wide operating temperature range, and low cost for numeric-only applications. The trend within this segment is towards higher efficiency materials (like AlInGaP replacing GaAsP), smaller package sizes, lower operating voltages, and integration of driver circuitry. However, the fundamental multiplexed, common-anode architecture of modules like the LTC-4624JF has proven enduringly effective for decades due to its electrical and conceptual simplicity.