LTC-4727JR LED Display Datasheet - 0.4-inch Digit Height - Super Red - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-4727JR is a quadruple-digit, seven-segment LED display module designed for applications requiring clear, high-visibility numeric readouts. With a digit height of 0.4 inches (10.0 mm), it offers excellent readability from a distance. The device utilizes advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology to produce a super red color output. This material system, grown on a non-transparent GaAs substrate, is known for its high efficiency and stability. The display features a gray face and white segments, which work in tandem to provide high contrast, enhancing character legibility under various lighting conditions. Its primary target markets include industrial control panels, test and measurement equipment, point-of-sale systems, and other electronic devices where reliable and bright numeric indication is critical.

1.1 Key Features

• 0.4-inch (10.0mm) Digit Height: Provides large, easily readable characters.
• Continuous Uniform Segments: Ensures a consistent and professional visual appearance without gaps or irregularities in the lit segments.
• Low Power Requirement: Efficient design suitable for battery-powered or energy-conscious applications.
• Excellent Character Appearance: High contrast between the gray face and white segments delivers sharp, well-defined numerals.
• High Brightness & High Contrast: The AlInGaP chips produce intense super red light, visible even in brightly lit environments.
• Wide Viewing Angle: Allows the display to be read clearly from a broad range of positions.
• Solid-State Reliability: LEDs offer long operational life, shock resistance, and vibration tolerance compared to other display technologies.
• Categorized for Luminous Intensity: Devices are binned for consistent brightness levels, aiding in multi-display applications.
• Lead-Free Package (RoHS Compliant): Manufactured in accordance with environmental regulations restricting hazardous substances.

1.2 Device Identification

The part number LTC-4727JR specifically denotes a multiplex common cathode display with AlInGaP super red LEDs and a right-hand decimal point configuration. This naming convention helps designers quickly identify the electrical configuration and optical characteristics of the component.

2. Mechanical and Packaging Information

The physical dimensions of the LTC-4727JR are critical for proper integration into end-product designs. The package is a standard through-hole type with pins for mounting on a printed circuit board (PCB). All primary dimensions are provided in millimeters, with a general tolerance of ±0.25 mm unless otherwise specified. Key mechanical notes include allowances for pin tip shift, limits on foreign material or ink contamination on the segment surface, and maximum allowable bubble size within the segment area. A slight bending of the reflector is permissible up to 1% of its length. For optimal mechanical fit and reliable solder joints, a PCB hole diameter of 0.9 mm is recommended for the display pins.

3. Electrical Configuration and Pinout

3.1 Internal Circuit Diagram

The LTC-4727JR employs a multiplexed common cathode architecture. This means the cathodes of the LEDs for each digit are connected together internally, while the anodes for each segment (A through G, and DP) are shared across all four digits. This design significantly reduces the number of required driver pins from 32 (4 digits * 8 segments) to just 12, making it highly efficient for microcontroller interfacing.

3.2 Pin Connection Details

The 16-pin dual in-line package has the following pin assignments:
Pin 1: Common Cathode for Digit 1
Pin 2: Common Cathode for Digit 2
Pin 3: Anode for Segment D
Pin 4: Common Cathode for Segments L1, L2, L3 (likely for colons or other indicators)
Pin 5: Anode for Segment E
Pin 6: Common Cathode for Digit 3
Pin 7: Anode for Decimal Point (DP)
Pin 8: Common Cathode for Digit 4
Pin 9: No Connection
Pin 10: No Pin
Pin 11: Anode for Segment F
Pin 12: No Pin
Pin 13: Anode for Segment C and L3
Pin 14: Anode for Segment A and L1
Pin 15: Anode for Segment G
Pin 16: Anode for Segment B and L2
Pins 9, 10, and 12 are not connected or are missing, which is a common practice in display pinouts to standardize package size.

4. Ratings and Characteristics

4.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. They are specified at an ambient temperature (Ta) of 25°C.
Power Dissipation per Segment: 70 mW maximum.
Peak Forward Current per Segment: 90 mA, but only under pulsed conditions (1/10 duty cycle, 0.1 ms pulse width). This rating is for brief, high-current multiplexing.
Continuous Forward Current per Segment: 25 mA at 25°C. This current must be derated linearly by 0.33 mA for every degree Celsius above 25°C to prevent overheating.
Operating & Storage Temperature Range: -35°C to +85°C.
Solder Condition: The display can withstand wave or hand soldering where the solder is applied 1/16 inch (approx. 1.6 mm) below the seating plane for a maximum of 3 seconds at 260°C. The unit's body temperature must not exceed the maximum rating during assembly.

4.2 Electrical and Optical Characteristics

These are the typical operating parameters at Ta=25°C, which define the device's performance under normal use.
Average Luminous Intensity (Iv): Ranges from a minimum of 320 µcd to a typical 975 µcd per segment when driven at a forward current (IF) of 1 mA. This high brightness is a key feature.
Peak Emission Wavelength (λp): 639 nm, placing the output in the super red region of the spectrum.
Spectral Line Half-Width (Δλ): 20 nm, indicating the spectral purity of the emitted light.
Dominant Wavelength (λd): 631 nm, with a tight tolerance of ±1 nm, ensuring consistent color output across units.
Forward Voltage per Chip (VF): Typically 2.6V at IF=20 mA, with a range from 2.0V to 2.6V and a tolerance of ±0.1V. This parameter is crucial for driver circuit design.
Reverse Current per Segment (IR): Maximum of 100 µA when a reverse voltage (VR) of 5V is applied. Note that this is a test condition; continuous reverse bias operation is prohibited.
Luminous Intensity Matching Ratio: 2:1 maximum for LEDs within similar light areas. This means the brightest segment in a display will be no more than twice as bright as the dimmest, ensuring uniformity.
Cross Talk Specification: ≤ 2.5%, minimizing unwanted illumination of non-selected segments during multiplexing.

4.3 Typical Performance Curves Analysis

While specific curve data points are not provided in the excerpt, typical curves for such a device would include:
Forward Current vs. Forward Voltage (I-V Curve): Shows the exponential relationship, critical for determining the required drive voltage for a target current. The curve will shift with temperature.
Luminous Intensity vs. Forward Current (I-L Curve): Demonstrates how light output increases with current, typically in a near-linear relationship within the operating range, before efficiency drops at very high currents.
Luminous Intensity vs. Ambient Temperature: Shows the derating of light output as the junction temperature increases. AlInGaP LEDs generally exhibit good high-temperature performance compared to other technologies.
Spectral Distribution: A graph plotting relative intensity against wavelength, centered around 639 nm with a 20 nm half-width, confirming the super red color point.

5. Application Guidelines and Design Considerations

5.1 General Application Notes

This display is intended for standard commercial and industrial electronic equipment. For applications with exceptional reliability requirements or where failure could risk safety, consultation is mandatory before design-in. Adherence to absolute maximum ratings is essential to avoid damage. Exceeding recommended drive currents or operating temperatures will accelerate light output degradation and can lead to premature failure. The driving circuit must incorporate protection against reverse voltages and transient spikes during power cycling. A constant current drive scheme is strongly recommended over constant voltage to ensure stable luminous intensity regardless of forward voltage variations. The circuit must be designed to accommodate the full VF range (2.0V to 2.6V) to guarantee the intended current is delivered to all segments.

5.2 Circuit Design and Thermal Management

The safe operating current must be selected based on the maximum expected ambient temperature, applying the specified derating factor of 0.33 mA/°C above 25°C. Reverse bias must be strictly avoided in circuit design, as it can induce metal migration within the LED chip, increasing leakage current or causing a short circuit. Designers should implement current-limiting resistors or dedicated LED driver ICs configured for common cathode multiplexing. Rapid ambient temperature changes, especially in humid environments, should be avoided as they can cause condensation on the display, potentially leading to electrical or optical issues.

5.3 Mechanical and Assembly Considerations

During assembly, avoid applying abnormal force to the display body. If a decorative film or filter is applied using pressure-sensitive adhesive, it is not recommended to let this film make direct, tight contact with the front panel, as external force may cause it to shift. For applications using two or more displays in one set, it is highly recommended to use displays from the same luminous intensity bin to prevent noticeable brightness or hue differences between units. If the end product requires the display to undergo drop or vibration testing, the specific test conditions should be evaluated in advance to ensure compatibility.

6. Storage and Handling

To maintain solderability and performance, the LED displays should be stored in their original moisture-barrier packaging under controlled conditions: temperature between 5°C and 30°C, and relative humidity below 60%. Prolonged storage outside these conditions, or with the moisture barrier bag opened for more than six months, can lead to pin oxidation. It is advised to manage inventory to avoid long-term storage and to consume products in a timely manner. If oxidation is suspected, re-tinning of the pins may be necessary before use.

7. Technical Comparison and Differentiation

The LTC-4727JR differentiates itself through its use of AlInGaP technology for super red emission. Compared to older GaAsP or GaP-based red LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current. The gray face/white segment combination provides superior contrast compared to displays with diffused or tinted faces. The multiplexed common cathode design is a standard but efficient architecture for multi-digit displays, reducing system cost and complexity. Its 0.4-inch digit size positions it between smaller indicators and larger panel displays, making it ideal for equipment where information needs to be read from a moderate distance.

8. Frequently Asked Questions (FAQ)

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λp) is the wavelength at which the emission spectrum has its maximum intensity (639 nm). Dominant wavelength (λd) is the single wavelength of monochromatic light that would match the perceived color of the LED (631 nm). λd is more relevant for color specification.

Q: Why is constant current drive recommended?
A: LED brightness is primarily a function of current, not voltage. The forward voltage (VF) can vary from unit to unit and with temperature. A constant current source ensures that the desired luminous intensity is achieved consistently, regardless of these VF variations.

Q: How do I calculate the series resistor for this display if I'm not using a dedicated driver IC?
A: For a simple static drive (not multiplexed), use Ohm's Law: R = (Vsupply - VF_total) / IF. VF_total is the sum of forward voltages for series-connected segments (if any). Choose IF within the continuous rating (e.g., 10-20 mA) and ensure power dissipation in the resistor is acceptable. For multiplexed drives, use the peak current rating and duty cycle to calculate average current.

Q: What does \"categorized for luminous intensity\" mean?
A: During manufacturing, displays are tested and sorted (binned) based on their measured light output at a standard test current. This allows designers to purchase units from the same brightness bin, ensuring visual uniformity when multiple displays are used side-by-side.

9. Design and Usage Case Study

Scenario: Designing a benchtop digital multimeter display.
The LTC-4727JR is an excellent candidate. Its 0.4-inch digits provide clear readability on a workbench. The designer would use a microcontroller with sufficient I/O pins to drive the four common cathodes and the 7-8 segment anodes in a time-division multiplexed manner. A dedicated LED driver port expander could also be used to offload this task from the MCU. The circuit would include current-limiting resistors on each segment anode line. The current value would be chosen (e.g., 15 mA) to provide ample brightness while staying within the derated limits for the expected maximum internal enclosure temperature (e.g., 50°C). The super red color is easy on the eyes for prolonged viewing. Care would be taken in the PCB layout to place the display away from major heat sources like voltage regulators. A filtered, stable power supply would be used to avoid voltage spikes. Finally, a neutral density filter or anti-glare window might be placed over the display to enhance contrast in bright lab lighting, taking care not to apply pressure that could shift a decorative film if used.