LTC-4724JS LED Digital Tube Datasheet - 0.4 Inch Character Height - AlInGaP Yellow Light - 2.6V Forward Voltage - 40mW Power Consumption - Technical Documentation

1. Product Overview

LTC-4724JS is a compact, high-performance three-digit seven-segment digital display module, specifically designed for applications requiring clear numeric readouts. Its primary function is to visually display three digits (0-9) and the corresponding decimal points through independent LED segments. This device is designed for integration into various electronic systems where space efficiency, readability, and reliability are key considerations.

Its core technology utilizes Aluminum Indium Gallium Phosphide (AlInGaP) semiconductor material to manufacture the LED chips. This material system is renowned for its high efficiency and excellent performance in the yellow to red spectral regions. The chips are fabricated on an opaque Gallium Arsenide (GaAs) substrate, which helps direct the light output forward, thereby enhancing brightness and contrast. The display features a gray panel with white segment markings, providing a high-contrast background that improves character legibility under various lighting conditions.

The display employs a common-cathode configuration with dynamic scanning. Compared to static driving methods, this design significantly reduces the number of required driver pins. Instead of requiring a dedicated pin for each segment of each digit, it connects the cathodes of each digit together and controls them sequentially (dynamic scanning), while the anodes for each segment type (A-G, DP) are shared across all digits. This makes it particularly suitable for microcontroller systems with limited I/O pins.

2. In-depth Technical Parameter Analysis

2.1 Photometric and Optical Characteristics

Optical performance is the core of display functionality. Key parameters are measured under standardized test conditions, typically at an ambient temperature (Ta) of 25°C.

• Average luminous intensity (I_V):This parameter defines the perceived brightness of a single segment. At a test current (I_F) of 1mA, the typical value is 650 µcd (microcandelas), with a minimum guaranteed value of 200 µcd. This wide range indicates the existence of a classification or binning process for luminous intensity, which is common in LED manufacturing to ensure a minimum performance level.
• Peak Emission Wavelength (λ_p):Measured under conditions of I_F=20mA, the typical peak wavelength is 588 nanometers (nm). This places its emitted light strictly within the yellow region of the visible spectrum.
• Dominant Wavelength (λ_d):This value is 587 nm, very close to the peak wavelength. The dominant wavelength is the single wavelength that best represents the perceived color of the light and is crucial for applications with strict color requirements.
• Spectral line half-width (Δλ):The typical value is 15 nm. This parameter indicates the spectral purity or bandwidth of the emitted light. As shown in this example, the relatively narrow half-width is characteristic of AlInGaP LEDs, contributing to the generation of saturated, pure yellow.
• Luminous intensity matching ratio (I_V-m):Wannan rabo ya ƙayyade cewa bai wuce 2:1 ba, yana bayyana bambancin haske da aka yarda tsakanin sassa daban-daban a cikin allon nuni iri ɗaya. Rabon 2:1 yana nufin cewa hasken mafi haske bai kamata ya wuce sau biyu na hasken mafi duhu ba a ƙarƙashin yanayin tuƙi iri ɗaya, don tabbatar da daidaiton bayyanar.

Duk ma'aunin ƙarfin haske ana yin su ta amfani da haɗakar firikwensin haske da matatar da aka daidaita don kusantar da daidaitaccen lanƙwasa amsa na gani na CIE (Kwamitin Duniya na Haskakawa), don tabbatar da cewa sakamakon ma'auni ya dace da fahimtar gani na ɗan adam.

2.2 Electrical Characteristics and Absolute Maximum Ratings

Adhering to these limits is crucial for device longevity and preventing catastrophic failure.

• Continuous forward current per segment:At 25°C, the maximum permissible continuous DC current through any single LED segment is 25 mA. Above this temperature, the rating must be linearly derated by 0.33 mA for every 1°C increase in ambient temperature.
• Peak forward current per segment:For pulsed operation, higher currents are permissible. Under conditions of a 1/10 duty cycle and a pulse width of 0.1 ms, the peak current can reach 60 mA. This is useful in dynamic scanning schemes to achieve higher instantaneous brightness during brief on-times.
• Power dissipation per segment:The maximum power dissipated as heat for a single segment is 40 mW. This value is calculated as the forward voltage (V_F) multiplied by the forward current (I_F). Exceeding this limit risks overheating and damaging the semiconductor junction.
• Forward voltage (V_F):At a drive current of 20 mA, the typical forward voltage drop of an LED segment is 2.6V, with a minimum of 2.05V. This parameter is crucial for designing the current limiting circuit in the driver.
• Reverse voltage per segment:The maximum reverse bias voltage that can be applied to an LED segment is 5V. Exceeding this value may cause immediate and irreversible damage to the LED due to junction breakdown.
• Reverse current per segment (I_R):When a 5V reverse bias is applied, the leakage current is typically 100 µA or less.

2.3 Thermal and Environmental Specifications

• Operating Temperature Range:The device is specified for normal operation within an ambient temperature range of -35°C to +85°C. Performance outside this range is not guaranteed.
• Storage temperature range:The device can be stored non-operationally within the same -35°C to +85°C range.
• Soldering temperature:During the assembly process, the device can withstand a maximum soldering temperature of 260°C for a maximum duration of 3 seconds, measured at a point 1.6mm below the package mounting plane. This is crucial for wave soldering or reflow soldering processes.

3. Grading and Classification System

The datasheet clearly states that the device is "classified by luminous intensity." This implies a post-production sorting (binning) process. Although this excerpt does not provide specific binning codes, typical classification for such displays involves grouping units based on their measured luminous intensity under standard test currents. This ensures customers receive displays with a consistent minimum brightness level. For I_VThe specified minimum (200 µcd) and typical (650 µcd) values define the boundaries for this classification. Designers should note that brightness variations may exist within the specified 2:1 matching ratio and across different intensity bins, which could affect system calibration for uniform brightness across multiple displays.

4. Performance Curve Analysis

The datasheet references "Typical Electrical/Optical Characteristic Curves," which are crucial for detailed design work. Although specific graphs are not provided in the text, based on standard LED characteristics, these curves typically include:

• Forward Current vs. Forward Voltage (I-V Curve):This nonlinear curve shows the relationship between the voltage applied across the LED and the resulting current. It is crucial for designing constant current drivers, as a small change in voltage can cause a large change in current (and thus brightness). The curve's knee region near the typical V_F(2.6V at 20mA) is the normal operating area.
• Luminous Intensity vs. Forward Current (I-L Curve):This graph shows how the light output increases with the drive current. It is typically linear within a certain range but saturates at very high currents due to thermal effects and efficiency droop._VThe 1mA test point and the 20mA point for other parameters provide two key references for this curve.
• Luminous Intensity vs. Ambient Temperature:The light output of an LED typically decreases as the junction temperature increases. For applications operating over a wide temperature range, this curve is crucial to ensure readability is maintained even at high temperatures.
• Spectral Distribution:A plot of relative intensity versus wavelength, showing a peak at ~588 nm and a narrow half-width of 15 nm, confirms pure yellow light emission.

5. Mechanical and Packaging Information

5.1 Physical Dimensions and Tolerances

The package drawing provides critical mechanical data for PCB layout and enclosure design. All dimensions are in millimeters. The general tolerance for unspecified dimensions is ±0.25 mm (equivalent to ±0.01 inches). Designers must incorporate these tolerances into their mechanical designs to ensure proper assembly. The drawing will detail the overall length, width, and height of the display module, the spacing between digits, segment dimensions, and the position and diameter of mounting pins.

5.2 Pin Configuration and Connection Diagram

The pin connection table is an interface map between the internal circuit and the external world. The LTC-4724JS employs a 15-pin arrangement (several of which are marked as "No Connection" or "No Pin").

• Common Cathode:Pins 1, 5, 7, and 14 are cathode connections. Pin 1 corresponds to digit 1, pin 5 corresponds to digit 2, pin 7 corresponds to digit 3, and pin 14 is the common cathode for the left-side decimal points (L1, L2, L3). This configuration enables a dynamic scanning scheme.
• Segment Anode:The remaining pins (2, 3, 4, 6, 8, 11, 12, 15) are anodes for specific segments: A, B, C, D, E, F, G, and DP (decimal point). As shown in the internal circuit diagram, segment C and G share connections with the left-side decimal point L3 and the common point, respectively.

The internal circuit diagram visually demonstrates this dynamic scanning architecture, showing how the three digit cathodes and the shared segment anodes are interconnected. Understanding this diagram is crucial for developing correct software timing and hardware drive circuits.

6. Welding and Assembly Guide

The absolute maximum rating for soldering temperature (260°C for 3 seconds, measured 1.6mm below the seating plane) provides clear guidance for the assembly process. This rating is compatible with standard lead-free reflow temperature profiles (peak temperature typically around 245-250°C). For wave soldering, the time pins are in contact with molten solder must be controlled to stay within this limit. It is recommended to follow IPC guidelines for through-hole component soldering. Preheating is advised to minimize thermal shock. After soldering, the display should be allowed to cool gradually. Proper ESD (Electrostatic Discharge) handling procedures should always be followed during assembly to prevent damage to the sensitive LED junctions.

7. Application Suggestions and Design Considerations

7.1 Typical Application Scenarios

LTC-4724JS yana dacewa da aikace-aikace daban-daban waɗanda ke buƙatar nuni na lamba mai ƙarfi, mai haske, kuma amintacce. Amfanin gama-gari sun haɗa da:

• Kayan aikin gwaji da aunawa:Digital multimeters, frequency counters, power supplies, inda ƙudurin lamba 3 ya isa (misali nuna 0-999).
• Industrial Control and Instrumentation:Panel meters for temperature, pressure, speed, or counting.
• Consumer Electronics:Audio equipment (amplifier volume display), kitchen appliances (timer, temperature reading).
• Automotive aftermarket:The datasheet claims "wide viewing angle" and "high contrast". The grey panel/white segments enhance contrast. For optimal viewing, the display should be mounted perpendicular to the primary viewing direction. High brightness (typical 650 µcd) is beneficial under high ambient light conditions.

7.2 Key Design Considerations

• Drive Circuit:A dynamic scanning drive circuit is required. This typically involves a microcontroller or a dedicated display driver IC, which can sink current for the common cathodes (usually via transistors) and source current from the segment anodes. Current-limiting resistors must be provided for each segment anode (which may be shared if constant-current drivers are used) to set I_Fto a safe value, typically between 10-20 mA, to balance brightness and lifespan.
• Dynamic scanning frequency:The refresh rate must be high enough to avoid visible flicker, typically above 60 Hz. For three-digit displays, each digit is illuminated for approximately one-third of the cycle time. The peak current can be set higher (up to the 60mA pulse rating) to compensate for the reduced duty cycle and maintain average brightness.
• Power supply:The forward voltage requirement (approximately 2.6V) implies that the system power supply must provide a voltage higher than this value to leave margin for the voltage drop across the current-limiting resistor and the drive circuit. A common 5V power supply is both convenient and reliable.
• Viewing Angle and Contrast:The datasheet claims a "wide viewing angle" and "high contrast." The gray face/white segments enhance contrast. For optimal viewing, the display should be mounted perpendicular to the primary viewing direction. In high-ambient-light conditions, the high brightness (650 µcd typ.) is beneficial.
• Thermal Management:Although the power consumption per segment is low, the cumulative heat generated when multiple segments are illuminated simultaneously (especially at higher currents) should be considered. Adequate ventilation in the enclosure is recommended, particularly when operating near the upper temperature limit.

8. Technical Comparison and Differentiation

The key differentiating factors for the LTC-4724JS lie in its material technology and packaging. Compared to older technologies like standard GaP or GaAsP LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in higher brightness at the same drive current. The resulting yellow color is also more saturated and pure. Compared to contemporary alternatives, its 0.4-inch character height provides a specific balance between size and readability. The dynamic scanning common-cathode design is standard for multi-digit displays, but the specific pinout and internal circuitry (including the shared cathode for the left decimal point) are unique to this model and must be matched by the driving software. The luminous intensity classification provides a degree of quality control that may not be present in all displays.

9. Frequently Asked Questions (Based on Technical Specifications)

• Q: Can I drive this display with a 3.3V microcontroller?A: It is possible, but requires careful design. Typical V_Fis 2.6V. Considering the small voltage drops across the driving transistor and the current-limiting resistor, the headroom from a 3.3V power supply may be very tight or insufficient, especially considering V_Ffluctuations. A 5V power supply is more reliable. You may need a level shifter or a driver IC powered by an independent 5V power rail.
• Q: Why is the peak current (60mA) higher than the continuous current (25mA)?A: If the duty cycle is low, the LED can withstand higher instantaneous current because the average power consumption and junction temperature remain within safe limits. This is used in dynamic scanning to achieve higher perceived brightness.
• Q: What is the purpose of the "No Connection" pin?A: They are likely mechanical placeholders to accommodate the standard 15-pin DIP (Dual In-line Package) package size. They provide physical stability during the soldering process but have no electrical function. Do not connect them to any circuit.
• Q: How to calculate the value of the current limiting resistor?A: Amfani da dokar Ohm: R = (V_{Power supply}- V_F- V_{Drive voltage drop}) / I_F. For a 5V power supply, V_Fis 2.6V, the drive voltage drop is 0.2V, the expected I_FFor 15mA: R = (5 - 2.6 - 0.2) / 0.015 = 146.7 Ω. A standard 150 Ω resistor is suitable. Be sure to verify the resistor's power dissipation: P = I²* R.

10. Practical Design and Usage Examples

Consider designing a simple 3-digit voltmeter using a microcontroller. The microcontroller's ADC reads the voltage, converts it to a number between 0 and 999, and needs to display it.

1. Hardware Interface:Configure three microcontroller I/O pins as outputs to control NPN transistors (or a transistor array) sinking current from the three digit cathode pins (1, 5, 7). Configure another eight I/O pins (or a shift register used to save pins) as outputs to source current through individual 150Ω current-limiting resistors to the eight segment anode pins (A, B, C, D, E, F, G, DP).
2. Software Routine:The main loop implements dynamic scanning. It turns off all digit cathodes. Then it sets the segment pattern (e.g., to display "5") on the anode pins for digit 1. Next, it enables (provides a ground path via a transistor) the cathode for digit 1. It waits for a short time (e.g., 2-3 milliseconds). Then it disables digit 1, sets the segment pattern for digit 2, enables the cathode for digit 2, waits, and repeats this process for digit 3. This cycle repeats continuously. The peak current per segment can be set to about 20mA. With a 1/3 duty cycle, the average current is about 6.7mA, well within the continuous rating.
3. Results:Due to the persistence of vision effect, all three digits appear to be lit simultaneously and steadily, displaying the measured voltage value.

11. Introduction to Technical Principles

LTC-4724JS is based on solid-state lighting technology using AlInGaP (aluminum indium gallium phosphide) semiconductors. When a forward voltage exceeding the diode's bandgap voltage is applied, electrons and holes are injected into the active region of the semiconductor structure. They recombine, releasing energy in the form of photons (light). The specific composition of the AlInGaP alloy determines the bandgap energy, which directly dictates the wavelength (color) of the emitted light—in this case, yellow (approximately 587-588 nm). The opaque GaAs substrate absorbs any backward-emitted light, improving overall efficiency by reducing internal reflections that do not contribute to effective forward light output. The seven-segment format is a standardized method for forming numeric characters by selectively illuminating seven independent bar-shaped LED segments (labeled A through G).

12. Technical Trends and Background

Ko da yake wannan takamaiman samfurin yana amfani da fasahar AlInGaP da ta kware, fagen nuni na LED gabaɗaya yana ci gaba da haɓaka. Abubuwan da ke faruwa sun haɗa da amfani da kayan aiki masu inganci (kamar InGaN don haske mai shuɗi/kore/fari), haɓaka ɗaurin guntu akan allon (COB) da na'urorin da aka ɗora a saman (SMD) don samun mafi girman yawa da ƙananan girma, da kuma haɗa direbobi da masu sarrafawa kai tsaye cikin na'urar nuni (nuni mai hankali). Duk da haka, don takamaiman aikace-aikacen da ke buƙatar tsantsar haske mai rawaya mai inganci a cikin daidaitaccen ɗaurin rami, nunin da ya dogara da AlInGaP (kamar LTC-4724JS) har yanzu shine amintaccen da tsada mai tsada. Sauƙinsu, ƙarfin su, da sauƙin haɗawa da na'urar sarrafawa ta asali, suna tabbatar da cewa suna ci gaba da kasancewa masu dacewa a yawancin ƙira na masana'antu da na mabukaci waɗanda ba sa buƙatar nunin zane na al'ada.