LTC-2621JR LED Display Datasheet - 0.28-inch Digit Height - Super Red Color - 2.6V Forward Voltage - Low Power - English Technical Document

1. Product Overview

The LTC-2621JR is a compact, dual-digit, seven-segment light-emitting diode (LED) display module. Its primary function is to provide clear, legible numeric output in a wide range of electronic devices and instrumentation. The core technology is based on AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material, which is engineered to produce a super red color with high luminous efficiency. The device is characterized by its low current operation, making it suitable for battery-powered or energy-conscious applications where minimizing power draw is critical. The display features a gray face and white segment color, which enhances contrast and readability under various lighting conditions.

1.1 Core Advantages

• Low Power Requirement: Engineered for operation at very low forward currents, with segments designed to be driven effectively at currents as low as 1 mA. This significantly reduces overall system power consumption.
• High Brightness & Contrast: Utilizes AlInGaP technology to deliver high luminous intensity, ensuring excellent visibility. The gray face/white segment design further improves contrast ratios.
• Excellent Character Appearance: Features continuous, uniform segments (0.28-inch/7.0 mm digit height) for consistent and professional-looking numeric characters.
• Wide Viewing Angle: Provides clear visibility from a broad range of angles, which is essential for user interfaces.
• Solid-State Reliability: As an LED-based device, it offers long operational life, shock resistance, and reliability compared to mechanical or other display technologies.
• Categorized for Luminous Intensity: Devices are binned or categorized based on their light output, allowing for better consistency in applications requiring uniform brightness across multiple displays.

2. Technical Parameter Deep-Dive

This section provides a detailed, objective analysis of the key electrical and optical parameters specified 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 beyond which permanent damage to the device may occur. Operation outside these limits is not guaranteed and should be avoided.

• Power Dissipation per Segment: 70 mW maximum. This limit is determined by the LED chip's ability to dissipate heat. Exceeding this can lead to thermal runaway and failure.
• Peak Forward Current per Segment: 100 mA maximum, but only under pulsed conditions (1/10 duty cycle, 0.1 ms pulse width). This rating is for multiplexing or brief overdrive scenarios, not for continuous DC operation.
• Continuous Forward Current per Segment: 25 mA maximum at 25°C. This current derates linearly at 0.33 mA/°C as ambient temperature (Ta) increases above 25°C. For example, at 85°C, the maximum allowable continuous current would be approximately: 25 mA - ((85°C - 25°C) * 0.33 mA/°C) = ~5.2 mA. This derating is critical for thermal management.
• Reverse Voltage per Segment: 5 V maximum. LEDs have a low reverse breakdown voltage. Applying a reverse voltage greater than this can cause immediate and catastrophic failure of the PN junction.
• Operating & Storage Temperature Range: -35°C to +85°C. The device is rated for industrial temperature ranges.
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds, measured 1.6 mm below the seating plane. This is a standard reflow soldering profile guideline to prevent damage to the plastic package and internal wire bonds.

2.2 Electrical & Optical Characteristics

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

• Average Luminous Intensity (I_V): 200 μcd (Min), 600 μcd (Typ) at I_F = 1 mA. This is the key brightness parameter at the recommended low-current operating point. The wide range (200-600) indicates the device is binned; designers must account for this variation or specify a bin for consistent brightness.
• Peak Emission Wavelength (λ_p): 639 nm (Typ) at I_F = 20 mA. This is the wavelength at which the optical power output is maximum. It defines the \"super red\" color.
• Spectral Line Half-Width (Δλ): 20 nm (Typ) at I_F = 20 mA. This measures the spectral purity or bandwidth of the emitted light. A value of 20 nm is typical for AlInGaP red LEDs and indicates a relatively pure color.
• Dominant Wavelength (λ_d): 631 nm (Typ) at I_F = 20 mA. This is the single wavelength perceived by the human eye that best matches the color of the LED. It is slightly shorter than the peak wavelength.
• Forward Voltage per Segment (V_F): 2.0 V (Min), 2.6 V (Typ) at I_F = 20 mA. This is the voltage drop across the LED when conducting. It is crucial for calculating series resistor values. The typical 2.6V is higher than standard GaAsP red LEDs, which is characteristic of AlInGaP technology.
• Reverse Current per Segment (I_R): 100 μA (Max) at V_R = 5 V. This is the small leakage current that flows when the LED is reverse-biased at its maximum rating.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max). This specifies the maximum allowable ratio between the brightest and dimmest segment within a single device or between devices. A ratio of 2:1 means the dimmest segment can be no less than half as bright as the brightest, ensuring uniformity.

3. Binning System Explanation

The datasheet indicates the device is \"Categorized for Luminous Intensity.\" This refers to a binning process.

• Luminous Intensity Binning: After manufacture, LEDs are tested and sorted into different bins based on their measured light output at a standard test current (e.g., 1 mA or 20 mA). The LTC-2621JR's I_V range (200-600 μcd) likely encompasses several bins. Using LEDs from the same bin in a multi-digit or multi-unit application ensures consistent brightness across the display, which is critical for product aesthetics and readability. Designers can often specify a particular intensity bin code when ordering.
• Forward Voltage Binning: While not explicitly mentioned for this part, voltage binning is also common. Grouping LEDs by similar V_F can help in designing simpler, more uniform current-limiting networks, especially in parallel or multiplexed configurations.

4. Performance Curve Analysis

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

• Relative Luminous Intensity vs. Forward Current (I_V / I_F Curve): This graph would show how light output increases with current. For LEDs, the relationship is generally linear at lower currents but can saturate at higher currents due to thermal effects. The curve confirms the device's usability at very low currents (1 mA).
• Forward Voltage vs. Forward Current (V_F / I_F Curve): This exponential curve is critical for determining the dynamic resistance of the LED and for designing constant-current drivers. It shows the V_F increasing with I_F.
• Relative Luminous Intensity vs. Ambient Temperature: This curve demonstrates the thermal derating 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 across wavelengths, centered around 639 nm with a ~20 nm half-width. This defines the color characteristics.

5. Mechanical & Package Information

The LTC-2621JR comes in a standard dual-digit seven-segment LED package.

• Digit Height: 0.28 inches (7.0 mm).
• Package Dimensions: The datasheet includes a detailed dimensional drawing (not reproduced here). Key tolerances are ±0.25 mm (0.01\"), which is standard for this type of component. Designers must use these dimensions for PCB footprint design and panel cutouts.
• Pin Configuration: The device has a 16-pin configuration (some pins are \"No Connection\" or \"No Pin\"). It is a multiplex common anode type. The pinout is as follows:
  • Common Anodes: Pins 2 (Digit 1), 5 (Digit 2), 8 (Digit 3), and 13 (L1, L2, L3).
  • Segment Cathodes: Pins 1 (D), 3 (D.P.), 4 (E), 6 (C, L3), 7 (G), 12 (B, L2), 15 (A, L1), 16 (F).
  • Pins 9, 10, 11, 14 are noted as No Connection or No Pin.
• Internal Circuit Diagram: The datasheet shows the internal electrical connections. It confirms the common anode multiplex structure: all anodes for a given digit (and the optional LEDs L1-L3) are tied together internally, while the cathodes for each segment are separate. This allows the three digits to be controlled sequentially (multiplexed) using only one set of segment drivers.
• Polarity Identification: The package likely has a physical marker (a dot, notch, or beveled edge) to identify Pin 1. Correct orientation is essential to prevent damage during soldering and operation.

6. Soldering & Assembly Guidelines

Adherence to these guidelines is necessary to prevent thermal damage during the PCB assembly process.

• Reflow Soldering Profile: The maximum recommended condition is 260°C peak temperature for a maximum of 3 seconds. This is measured at 1.6 mm (1/16 inch) below the seating plane of the package (i.e., on the PCB). Standard lead-free reflow profiles typically fall within this limit, but the time above liquidus (TAL) should be controlled.
• Hand Soldering: If hand soldering is necessary, a temperature-controlled iron should be used. Contact time per pin should be minimized (typically < 3 seconds), and a heat sink (e.g., tweezers) can be used on the lead between the iron and the package body.
• Cleaning: Use only cleaning agents compatible with the LED's plastic lens material to avoid clouding or chemical damage.
• Storage Conditions: Store in a dry, anti-static environment within the specified temperature range (-35°C to +85°C). Moisture-sensitive devices should be kept in sealed bags with desiccant if they are not baked before use.

7. Application Suggestions

7.1 Typical Application Scenarios

• Portable Consumer Electronics: Digital multimeters, handheld test equipment, compact audio players, or fitness trackers where low power consumption is paramount.
• Industrial Instrumentation: Panel meters, process controllers, timer displays, and sensor readouts where reliability and wide temperature operation are required.
• Automotive Aftermarket Displays: Auxiliary gauges (voltmeters, clock) for interior use, though environmental sealing may be required.
• Home Appliances: Display for microwave ovens, coffee makers, or thermostats.
• Educational Kits: Ideal for electronics learning projects involving multiplexed displays and microcontroller interfacing.

7.2 Design Considerations

• Current Limiting: ALWAYS use series current-limiting resistors for each segment cathode line (or a constant-current driver). The resistor value is calculated using: R = (V_supply - V_F - V_{drop_driver}) / I_F. For a 5V supply, V_F of 2.6V, and desired I_F of 10 mA: R = (5 - 2.6) / 0.01 = 240 Ω. Use the maximum V_F from the datasheet for a conservative design.
• Multiplexing Drive: Since it's a common anode multiplex display, a microcontroller or driver IC must sequentially enable each digit's common anode (pins 2, 5, 8) while outputting the corresponding segment pattern on the cathode lines. The refresh rate must be high enough (>60 Hz) to avoid visible flicker.
• Peak Current in Multiplexing: When multiplexing N digits, the instantaneous current per segment during its ON time is typically N times the desired average current. For 3-digit multiplexing at an average of 3 mA per segment, the peak current would be ~9 mA. This must be checked against the Absolute Maximum Ratings (25 mA continuous, 100 mA pulsed).
• Viewing Angle: Position the display considering its wide viewing angle 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 & Differentiation

The LTC-2621JR differentiates itself in the market through specific technological choices.

• AlInGaP vs. Traditional GaAsP/GaP: Older red LEDs used GaAsP or GaP substrates, which had lower efficiency and produced a more orange-red light. AlInGaP technology offers significantly higher luminous efficiency (more light output per mA), better color purity (saturated red at ~631-639 nm), and superior temperature stability. This translates to brighter displays 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 selected for excellent performance at very low currents (1 mA typ.), making it a specialist component for ultra-low-power designs.
• Gray Face/White Segment: This aesthetic choice improves contrast when the display is off (black/gray appearance) and enhances segment definition when lit, compared to all-black or all-gray packages.

9. Frequently Asked Questions (Based on Technical Parameters)

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

Yes, typically. The typical forward voltage (V_F) is 2.6V at 20 mA. At a lower drive current (e.g., 5-10 mA), V_F will be slightly lower (e.g., 2.4V). A 3.3V GPIO pin can directly sink current through a series resistor to turn on a segment. Calculation: For a GPIO pin sinking 5 mA with a V_F of 2.4V, the resistor value would be (3.3V - 2.4V) / 0.005A = 180 Ω. Ensure the microcontroller's total sink current capability is not exceeded.

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

The range represents the binning spread. To ensure consistency, you have two options: 1) Design your circuit to work adequately across the entire range (e.g., ensure readability at the minimum 200 μcd). 2) Specify a tighter luminous intensity bin code when ordering components for production, ensuring all units in your batch have similar output. Consult the manufacturer's full binning documentation.

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

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

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

For a multiplexed design with N digits, M segments lit per digit on average, and a peak segment current I_peak, the approximate average power is: P_avg ≈ N * (M / 7) * I_peak * V_F * (1/N) = (M / 7) * I_peak * V_F. The (1/N) factor comes from the duty cycle of multiplexing. Example: Displaying \"88.8\" (M=7 segments) with I_peak=10 mA and V_F=2.6V: P_avg ≈ (7/7) * 0.01 * 2.6 = 0.026 W or 26 mW for the entire 3-digit display.

10. Design-in Case Study

Scenario: Designing a low-power, 3-digit battery-operated digital thermometer.

• Microcontroller: A low-power MCU running at 3.3V with GPIO pins capable of sinking 10 mA.
• Drive 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). Seven other GPIO pins drive the segment cathodes through current-limiting resistors.
• Current Setting: Target an average segment current of 2 mA for good visibility and long battery life. With 3-digit multiplexing, the peak current per segment will be ~6 mA. Using V_F = 2.5V (estimated at 6 mA), and a driver saturation voltage of 0.2V, the series resistor value is: R = (3.3V - 2.5V - 0.2V) / 0.006A ≈ 100 Ω.
• Software: The MCU timer triggers an interrupt at 180 Hz (60 Hz per digit * 3 digits). In the interrupt service routine, it turns off the previous digit's anode, updates the segment pattern for the next digit, and then turns on the new digit's anode.
• Result: The display consumes less than 15 mW, provides flicker-free readability, and leverages the LTC-2621JR's optimized low-current performance to maximize battery runtime.

11. Technology Principle Introduction

The 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 active region of the semiconductor, releasing energy in the form of photons (light). The specific composition of the AlInGaP layers determines the bandgap energy, which directly defines the wavelength (color) of the emitted light—in this case, red at ~639 nm. The light is emitted through the top of the chip, shaped by the plastic package lens to form the uniform segments. The common anode multiplex configuration is an internal wiring scheme that reduces the number of required external driver pins from (7 segments + 1 DP) * 3 digits = 24 down to 7 segment lines + 3 digit lines = 10, plus a few for optional LEDs, making it much more practical to interface with microcontrollers.

12. Technology Trends

While the LTC-2621JR represents a mature and reliable technology, the broader display landscape is evolving. The trend in informational displays is moving towards higher integration and flexibility. Organic LED (OLED) and micro-LED displays offer self-emissive, high-contrast, and flexible form factors. For simple numeric readouts, however, traditional segmented LED displays remain highly competitive due to their extreme simplicity, robustness, low cost, high brightness, and wide operating temperature range. The specific trend within this segment is towards even lower power consumption, higher efficiency materials (like improved AlInGaP or InGaN for other colors), and the integration of driver electronics (like I2C or SPI interfaces) directly into the display module, reducing external component count and simplifying design. The LTC-2621JR's focus on ultra-low-current operation aligns well with the enduring demand for energy-efficient components in portable and IoT devices.