LTC-2621JR LED Digital Tube Datasheet - 0.28 Inch Character Height - Super Bright Red - 2.6V Forward Voltage - Low Power Consumption - Technical Documentation

1. Product Overview

LTC-2621JR is a compact, dual-digit, seven-segment light-emitting diode (LED) digital display module. Its primary function is to provide clear, easily readable numerical output in a wide range of electronic devices and instrumentation. Its core technology is based on AlInGaP (aluminum indium gallium phosphide) semiconductor material, which is engineered to produce ultra-high brightness red light with high luminous efficiency. The device is characterized by low operating current, making it suitable for battery-powered or energy-sensitive applications where minimizing power consumption is crucial. The digital tube features a gray panel with white segment design to enhance contrast and readability under various lighting conditions.

1.1 Core Advantages

• Low Power Consumption Requirements:Designed specifically for operation at extremely low forward current, the segment codes can be effectively driven with currents as low as 1 mA. This significantly reduces the overall power consumption of the system.
• High brightness and high contrast:Utilizing AlInGaP technology, it provides high luminous intensity, ensuring excellent visibility. The gray panel/white segment code design further enhances the contrast.
• Excellent character appearance:Features continuous, uniform segment digits (0.28 inch/7.0 mm character height) for consistent and professional numeric display.
• Wide viewing angle:Provides clear visibility from a wide range of viewing angles, which is crucial for user interfaces.
• Solid-State Reliability:As an LED-based device, it offers longer service life, shock resistance, and reliability compared to mechanical or other display technologies.
• Graded by luminous intensity:Devices are graded or classified based on their light output, enabling better consistency in applications requiring uniform brightness across multiple displays.

2. In-depth Analysis of Technical Parameters

This section provides a detailed and objective analysis of the key electrical and optical parameters defined in the datasheet. Understanding these parameters is crucial for proper circuit design and ensuring optimal display performance.

2.1 Absolute Maximum Ratings

These ratings define the stress limits that may cause permanent damage to the device. Operation outside these limits is not guaranteed and should be avoided.

• Power consumption per segment:Maximum 70 mW. This limit is determined by the heat dissipation capability of the LED chip. Exceeding this value may lead to thermal runaway and failure.
• Peak forward current per segment:Maximum 100 mA, but only under pulse conditions (1/10 duty cycle, 0.1 ms pulse width). This rating is applicable for multiplexing or brief overdrive scenarios, not for continuous DC operation.
• Continuous forward current per segment:Maximum 25 mA at 25°C. This current linearly derates at a rate of 0.33 mA/°C when the ambient temperature (Ta) exceeds 25°C. For example, at 85°C, the maximum allowable continuous current is approximately: 25 mA - ((85°C - 25°C) * 0.33 mA/°C) = ~5.2 mA. This derating is crucial for thermal management.
• Reverse voltage per segment:Maximum 5 V. The reverse breakdown voltage of an LED is relatively low. Applying a reverse voltage exceeding this value may cause immediate catastrophic failure of the PN junction.
• Operating and storage temperature range:-35°C to +85°C. This device is suitable for the industrial temperature range.
• Welding Temperature:Maximum 260°C, up to 3 seconds, measured 1.6 mm below the mounting plane. This is the standard reflow soldering temperature profile guideline, designed to prevent damage to the plastic package and internal bonding wires.

2.2 Electrical and Optical Characteristics

These are typical operating parameters measured at Ta=25°C. Designers should use these values for circuit calculations.

• Average luminous intensity (I_V):At I_FCurve):
• Peak Emission Wavelength (λ_p):At I_F= 20 mA, 639 nm (typical). This is the wavelength at which the optical power output is maximum. It defines the color of "Ultra High Brightness Red".
• Spectral Line Half-Width (Δλ):At I_FAt I_F = 20 mA, 20 nm (typical). This measures the spectral purity or bandwidth of the emitted light. A value of 20 nm is typical for AlInGaP red LEDs, indicating relatively pure color.
• Dominant Wavelength (λ_D)_d):At I_FAt I_F = 20 mA, 631 nm (typical). This is the single wavelength that most closely matches the color perceived by the human eye. It is slightly shorter than the peak wavelength.
• Forward Voltage per Segment (V_F)_F):At I_FAt I_F = 20 mA, 2.0 V (min), 2.6 V (typical). This is the voltage drop when the LED is conducting. It is crucial for calculating the series resistor value. The typical 2.6V is higher than standard GaAsP red LEDs, which is characteristic of AlInGaP technology.
• Each reverse current (I_R):At V_R= 5 V, 100 μA (maximum). This is the small leakage current that flows when the LED is reverse-biased at its maximum rated value.
• Luminous intensity matching ratio (I_V-m):2:1 (maximum). This parameter specifies the maximum allowable ratio between the brightest and darkest segments within a single device or between devices. A ratio of 2:1 means the brightness of the darkest segment must not be less than half that of the brightest segment, thereby ensuring uniformity.

3. Explanation of the Grading System

The datasheet indicates that the device is "graded by luminous intensity." This refers to a grading process.

• Luminous Intensity Binning:After manufacturing, LEDs are tested and sorted into different bins based on their light output measured at a standard test current (e.g., 1 mA or 20 mA). The I_Vrange (200-600 μcd) of the LTC-2621JR may encompass multiple bins. Using LEDs from the same bin in multi-digit or multi-unit applications ensures uniform brightness across the display, which is crucial for product aesthetics and readability. Designers can often specify a particular luminous intensity bin code when ordering.
• Forward Voltage Binning:Although not explicitly mentioned for this device, voltage binning is also common. Grouping LEDs with similar V_Ffacilitates simpler and more uniform current-limiting network design, especially in parallel or multiplexed configurations.

4. Performance Curve Analysis

The datasheet references "Typical Electrical/Optical Characteristic Curves." Although specific charts are not provided in the text, we can infer their typical content and importance.

• Relative Luminous Intensity vs. Forward Current Curve (I_V/ I_FCurve):This chart will show how light output increases with current. For LEDs, the relationship is typically linear at lower currents but may saturate at higher currents due to thermal effects. This curve confirms the device's usability at extremely low currents (1 mA).
• Forward Voltage vs. Forward Current curve (V_F/ I_FCurve):This exponential curve is crucial for determining the LED's dynamic resistance and designing constant-current drivers. It shows V_FWith I_F.
• Increase.Relative luminous intensity vs. ambient temperature curve:
• This curve illustrates the thermal derating characteristics of light output. For AlInGaP LEDs, luminous intensity typically decreases as temperature increases. This is a key consideration for applications operating in high-temperature environments.Spectral Distribution:

A graph showing the relative optical power at each wavelength, with a center wavelength of approximately 639 nm and a half-width of about 20 nm. This defines the color characteristics.

Mechanical and Packaging Information

• LTC-2621JR uses a standard dual-digit seven-segment LED package.Character Height:
• 0.28 inch (7.0 mm).Package Dimensions:
• The datasheet contains a detailed dimensional drawing (not copied here). The key tolerance is ±0.25 mm (0.01 inches), which is the standard tolerance for this type of component. Designers must use these dimensions for PCB pad design and panel cutouts.Pin Configuration:
  • The device adopts a 16-pin configuration (some pins are "no connect" or "no pin"). It is a multiplexed common anode type. The pin arrangement is as follows:
  • Common anode: Pin 2 (Digit 1), Pin 5 (Digit 2), Pin 8 (Digit 3), and Pin 13 (L1, L2, L3).
  • Segment cathode: Pin 1 (D), Pin 3 (D.P.), Pin 4 (E), Pin 6 (C, L3), Pin 7 (G), Pin 12 (B, L2), Pin 15 (A, L1), Pin 16 (F).
• Pins 9, 10, 11, 14 are marked as No Connection or No Pin.Internal circuit diagram:
• The datasheet shows the internal electrical connections. It confirms a common-anode multiplexed structure: all anodes for a given digit (and optionally LEDs L1-L3) are internally connected together, while the cathode for each segment is separate. This allows the three digits to be controlled sequentially (multiplexed) using only one set of segment drivers.Polarity Identification:

The package may have physical markings (a dot, notch, or bevel) to identify pin 1. Correct orientation is crucial to prevent damage during soldering and operation.

6. Soldering and Assembly Guide

• Adhering to these guidelines is necessary to prevent thermal damage during PCB assembly.Reflow soldering temperature profile:
• The recommended maximum condition is a peak temperature of 260°C for a maximum of 3 seconds. This is measured 1.6 mm (1/16 inch) below the package mounting plane (i.e., on the PCB). Standard lead-free reflow profiles are typically within this limit, but the time above liquidus (TAL) should be controlled.手工焊接：<如果必须进行手工焊接，应使用温控烙铁。每个引脚的接触时间应最小化（通常
• 3 seconds), and a heat sink (e.g., tweezers) can be used on the pin between the iron and the package body.Cleaning:
• Use only cleaners compatible with LED plastic lens materials to avoid fogging or chemical damage.Storage Conditions:

A cikin kewayon zafin jiki da aka kayyade (-35°C zuwa +85°C), a adana a cikin yanayi mai bushewa, mai hana tashin wutar lantarki. Ga na'urori masu kula da danshi, idan ba a gasa kafin amfani ba, a ajiye a cikin jakar da aka rufe tare da abin bushewa.

7. Application Suggestions

• 7.1 Typical Application ScenariosPortable Consumer Electronics:
• Digital multimeters, handheld test equipment, compact audio players, or fitness trackers, where low power consumption is critical.Industrial Instrumentation:
• Panel meters, process controllers, timer displays, and sensor readings, requiring reliability and a wide operating temperature range.Automotive Aftermarket Displays:
• Auxiliary gauges for interior (voltmeter, clock), but may require environmental sealing.Household Appliances:
• Displays for microwave ovens, coffee makers, or thermostats.Educational kit:

An ideal choice for e-learning projects involving multiplexed displays and microcontroller interfaces.

• 7.2 Design ConsiderationsCurrent Limiting:_{A series current-limiting resistor (or constant current driver) must be used for each segment cathode line. The formula for calculating the resistor value is: R = (V}Power Supply_F- V_{Driver voltage drop}) / I_F. For a 5V power supply, V_FIt is 2.6V, the desired I_Fis 10 mA: R = (5 - 2.6) / 0.01 = 240 Ω. For a conservative design, please use the maximum V_Fvalue from the datasheet.
• Multiplexing drive:由于它是共阳极多路复用显示器，微控制器或驱动器IC必须顺序使能每个数字位的共阳极（引脚2、5、8），同时在阴极线上输出相应的段码图案。刷新率必须足够高（>60 Hz）以避免可见闪烁。
• Peak current in multiplexing:When multiplexing N digits, the instantaneous current through each segment during its on-time is typically N times the desired average current. For 3-digit multiplexing, with an average segment current of 3 mA, the peak current is approximately ~9 mA. This must be checked against the absolute maximum ratings (25 mA continuous, 100 mA pulse).
• Viewing angle:Considering its wide viewing angle, position the display to ensure optimal readability for the end user.
• ESD Protection:LEDs are sensitive to electrostatic discharge. Implement standard ESD handling procedures during assembly.

8. Technical Comparison and Differentiation

LTC-2621JR achieves market differentiation through specific technical choices.

• AlInGaP vs. Traditional GaAsP/GaP:Older red LEDs use GaAsP or GaP substrates, which are less efficient and produce a more orange-red light. AlInGaP technology offers significantly higher luminous efficiency (more light output per mA), better color purity (saturated red around 631-639 nm), and superior temperature stability. This means displays are brighter with lower power consumption or longer battery life.
• Low Current Optimization:Many seven-segment displays are characterized at 20 mA. The LTC-2621JR is explicitly tested and screened for excellent performance at very low currents (typically 1 mA), making it a specialized component for ultra-low-power designs.
• Grey Panel/White Segment:This aesthetic choice enhances contrast when the display is off (black/grey appearance) and improves segment clarity when lit, compared to an all-black or all-grey package.

9. Frequently Asked Questions (Based on Technical Specifications)

9.1 Can I drive this display directly with a 3.3V microcontroller without a level shifter?

Kwa kawaida inawezekana. Katika 20 mA, voltage ya mbele ya kawaida (V_F) ni 2.6V. Katika mkondo wa chini wa kuendesha (kwa mfano 5-10 mA), V_Fitakuwa chini kidogo (kwa mfano 2.4V). Pini ya GPIO ya 3.3V inaweza kuwasha sehemu moja kwa moja kwa kuingiza mkondo kupitia upinzani uliosanidiwa. Hesabu: Kwa kuingiza mkondo wa 5 mA, V_FFor a 2.4V GPIO pin, the resistor value is (3.3V - 2.4V) / 0.005A = 180 Ω. Ensure the total sink current capability of the microcontroller is not exceeded.

9.2 Why is the luminous intensity given as a range (200-600 μcd)? How to ensure brightness consistency?

This range represents a binning distribution. To ensure consistency, you have two options: 1) Design your circuit to function correctly across the entire range (e.g., ensure readability even at the minimum 200 μcd). 2) Specify a tighter luminous intensity binning code when ordering components for production, ensuring all units in your batch have similar output. Please consult the manufacturer's complete binning documentation.

9.3 What is the purpose of the "L1, L2, L3" connections mentioned with some cathodes?

These are connections to optional, independent LED indicators (which may be small dots or icons) that are part of the same package but are electrically independent from the seven-segment digit. They share a common anode (pin 13) but have independent cathodes (pin 15/L1, 12/L2, 6/L3). They can be used for symbols such as a colon, decimal points for other digits, or status indicators.

9.4 How do I calculate the power consumption of my display design?

Ga ƙira mai sarrafa yawa tare da lambobi N, kowane lamba yana kunna sassan M a matsakaita, da madaidaicin igiyar ruwa I_Madaidaicina sarrafa yawa, matsakaicin matsakaicin ƙarfin wuta kusan: P_Average≈ N * (M / 7) * I_Madaidaici* V_F* (1/N) = (M / 7) * I_Madaidaici* V_F. (1/N) factor comes from the duty cycle of multiplexing. Example: Display "88.8" (M=7 segments), I_Madaidaici=10 mA, V_F=2.6V: P_Average≈ (7/7) * 0.01 * 2.6 = 0.026 W, meaning the entire 3-digit display consumes 26 mW.

10. Design Case Study

Scenario:Design a low-power, 3-bit battery-powered digital thermometer.

• Microcontroller:A low-power MCU operating at 3.3V, whose GPIO pins can sink 10 mA of current.
• Driving Method:Multiplexing. Three GPIO pins are configured as outputs to drive the common anodes (digits 1, 2, 3) via small NPN transistors or MOSFETs (to handle the combined segment current). Another seven GPIO pins drive the segment cathodes through current-limiting resistors.
• Current Setting:The target average segment current is 2 mA for good visibility and long battery life. Using 3-way multiplexing, the peak current per segment is approximately ~6 mA. Using V_F= 2.5V (estimated at 6 mA), with a driver saturation voltage drop of 0.2V, the series resistor value is: R = (3.3V - 2.5V - 0.2V) / 0.006A ≈ 100 Ω.
• Software:MCU timer triggers an interrupt at 180 Hz (60 Hz per digit * 3 digits). In the Interrupt Service Routine, it turns off the anode of the previous digit, updates the segment pattern for the next digit, and then turns on the anode of the new digit.
• Result:This display consumes less than 15 mW, provides flicker-free readability, and utilizes the LTC-2621JR's optimized low-current performance to maximize battery runtime.

11. Technical Principle Introduction

LTC-2621JR is based on solid-state lighting technology. Each segment contains one or more AlInGaP LED chips. When a forward voltage exceeding the diode's threshold is applied, electrons and holes recombine in the semiconductor active region, releasing energy in the form of photons (light). The specific composition of the AlInGaP layer determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, red at approximately 639 nm. Light is emitted from the top of the chip and shaped by the plastic package lens to form uniform segments. The common-anode multiplexing configuration is an internal wiring scheme that reduces the number of required external drive pins from (7 segments + 1 decimal point) * 3 digits = 24 to 7 segment lines + 3 digit lines = 10, plus a few pins for optional LEDs, making its interface with a microcontroller more practical.

12. Teknoloji Trendleri

While the LTC-2621JR represents a mature and reliable technology, the broader display landscape is evolving. The trend in information display is toward higher integration and flexibility. Organic LED (OLED) and micro-LED displays offer self-emission, high contrast, and flexible form factors. However, for simple numeric readouts, traditional segmented LED displays remain highly competitive due to their minimalism, ruggedness, low cost, high brightness, and wide operating temperature range. Specific trends within this segment are toward lower power consumption, more efficient materials (such as improved AlInGaP or InGaN for other colors), and the direct integration of driving electronics (like I2C or SPI interfaces) into the display module, thereby reducing external component count and simplifying design. The LTC-2621JR's focus on ultra-low current operation aligns well with the enduring demand for highly energy-efficient components in portable and IoT devices.