LTC-4727JD LED Display Datasheet - 0.4-inch Digit Height - Hyper Red (650nm) - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTC-4727JD is a quadruple-digit, seven-segment alphanumeric display module designed for applications requiring clear, bright numeric readouts. Its primary function is to visually represent numerical data through individually addressable segments. The device is constructed using advanced AlInGaP (Aluminum Indium Gallium Phosphide) LED chips mounted on a non-transparent GaAs substrate. This material choice is critical for the device's performance, as AlInGaP semiconductors are renowned for their high efficiency and excellent luminous output in the red to amber spectral regions. The visual presentation features a gray faceplate with white segment markings, providing high contrast for optimal legibility under various lighting conditions.

The core advantage of this display lies in its solid-state reliability, stemming from the LED technology, which offers a significantly longer operational lifespan compared to legacy technologies like vacuum fluorescent or incandescent displays. It is categorized for luminous intensity, meaning units are binned and tested to ensure consistent brightness levels. The package is compliant with lead-free manufacturing requirements. The display's design prioritizes excellent character appearance, high brightness, and a wide viewing angle, making it suitable for both consumer and industrial interfaces where readability from multiple angles is essential.

1.1 Technical Parameters Deep Objective Interpretation

1.1.1 Photometric & Optical Characteristics

The optical performance is defined under standard test conditions at an ambient temperature (Ta) of 25\u00b0C. The key parameter, Average Luminous Intensity (Iv), has a specified range from a minimum of 200 \u00b5cd to a maximum of 650 \u00b5cd when driven at a forward current (IF) of 1mA. This range indicates the production binning process, where devices are sorted based on their actual output. The typical value serves as a central reference point for design calculations. The luminous intensity matching ratio for similar light areas is specified as 2:1 maximum, which is crucial for ensuring uniform brightness across all segments and digits, preventing a patchy or uneven appearance.

The color characteristics are defined by wavelength. The Peak Emission Wavelength (\u03bbp) is typically 650 nanometers (nm), placing the output in the hyper-red region of the spectrum. The Dominant Wavelength (\u03bbd) is specified as 639 nm. It is important to understand the distinction: peak wavelength is the point of maximum spectral power, while dominant wavelength is the single-wavelength perception of color by the human eye. The Spectral Line Half-Width (\u0394\u03bb) is 20 nm, indicating the narrow bandwidth of the emitted light, which contributes to a pure, saturated red color.

1.1.2 Electrical Parameters

The electrical characteristics define the operating boundaries and conditions for the device. The Absolute Maximum Ratings set the limits beyond which permanent damage may occur. The Continuous Forward Current per segment is rated at 25 mA. A derating factor of 0.33 mA/\u00b0C applies linearly from 25\u00b0C, meaning the maximum safe continuous current decreases as the ambient temperature increases. This is a critical design consideration for thermal management. For pulsed operation, a higher Peak Forward Current of 90 mA is allowed under specific conditions: a 1/10 duty cycle and a 0.1ms pulse width. This enables multiplexing schemes where higher instantaneous current can be used to achieve perceived brightness while keeping average power low.

The Forward Voltage (VF) per segment ranges from 2.1V to 2.6V at IF=20mA. This parameter is essential for designing the current-limiting circuitry, typically resistors or constant-current drivers. The Reverse Voltage (VR) rating is 5V, and the Reverse Current (IR) is a maximum of 100 \u00b5A at this voltage, indicating the diode's leakage characteristics in the off-state. Power Dissipation per segment is limited to 70 mW, which directly relates to the thermal design of the application.

1.1.3 Thermal & Environmental Specifications

The device is rated for an Operating Temperature Range of -35\u00b0C to +105\u00b0C. This wide range makes it suitable for applications in harsh environments, including industrial controls and automotive interiors (non-critical areas). The identical Storage Temperature Range ensures the device can withstand these extremes when not powered. The solder reflow condition is explicitly stated: the component can be subjected to 260\u00b0C for 3 seconds, measured 1/16 inch (approximately 1.59 mm) below the seating plane. This information is vital for PCB assembly processes to prevent thermal damage during soldering.

1.2 Binning System Explanation

The datasheet indicates the device is \"Categorized for Luminous Intensity.\" This implies a binning process where manufactured units are tested and sorted into groups (bins) based on their measured light output at a standard test current (likely 1mA or 20mA). Designers can select bins to ensure consistency in brightness across multiple displays in a single product. While not explicitly detailed with bin codes in this document, such a system allows procurement of parts with guaranteed minimum or typical luminous intensity, which is crucial for applications requiring uniform visual performance.

1.3 Performance Curve Analysis

The datasheet references \"Typical Electrical / Optical Characteristic Curves,\" which are essential tools for understanding device behavior beyond single-point specifications. Although the specific curves are not detailed in the provided text, typical curves for such devices would include:

• Relative Luminous Intensity vs. Forward Current (I-V Curve): This curve shows how light output increases with current. It is typically non-linear, with efficiency often dropping at very high currents due to thermal effects.
• Forward Voltage vs. Forward Current: This shows the diode's IV characteristic, important for calculating voltage drops and power supply requirements.
• Relative Luminous Intensity vs. Ambient Temperature: This curve demonstrates the thermal quenching effect, where LED output decreases as junction temperature rises. Understanding this is key for designs operating at high ambient temperatures.
• Spectral Distribution: A graph showing the relative power emitted across wavelengths, centered around the 650nm peak with the specified 20nm half-width.

These curves allow designers to optimize drive conditions for a balance of brightness, efficiency, and longevity.

2. Mechanical & Packaging Information

2.1 Dimensions & Outline Drawing

The package drawing provides critical mechanical data. All primary dimensions are specified in millimeters. The standard tolerance for these dimensions is \u00b10.25 mm unless a specific feature note states otherwise. An important note specifies a pin tip shift tolerance of +0.4 mm, which accounts for potential minor misalignment of the leads during the molding process, affecting PCB hole placement or socket design. The overall size is dictated by the 0.4-inch (10.0 mm) digit height, which refers to the physical height of a single numeric character.

2.2 Pinout & Connection Diagram

The device has a 16-pin configuration, though not all positions are populated or connected. It is configured as a Multiplex Common Cathode display. This architecture is fundamental to its operation:

• Common Cathodes: Pins 1, 2, 4, 6, and 8 are the common cathode connections for Digit 1, Digit 2, a group of segments (L1,L2,L3), Digit 3, and Digit 4, respectively. In a multiplexed scheme, these cathodes are switched to ground sequentially to select which digit is active.
• Segment Anodes: Pins 3, 5, 7, 11, 13, 14, 15, and 16 are the anode connections for the individual segments (A, B, C, D, E, F, G, DP) and some colon/punctuation segments (L1, L2, L3). The appropriate anodes are driven high (through a current-limiting resistor) to illuminate specific segments of the currently selected digit.
• The internal circuit diagram shows the interconnection of these anodes and cathodes, forming a matrix that allows control of 4 digits and a decimal point/colon with only 13 effective signal lines, instead of the 36+ lines a static drive would require.

3. Soldering & Assembly Guidelines

The absolute maximum ratings section provides the key soldering parameter: the device can withstand a solder temperature of 260\u00b0C for 3 seconds, measured at a point 1.59mm (1/16 inch) below the seating plane. This is a standard reflow profile reference. For hand soldering, a lower temperature and shorter contact time should be used to prevent localized overheating. It is critical to ensure the temperature of the LED package itself does not exceed the maximum storage temperature rating during any part of the assembly process. Proper ESD (Electrostatic Discharge) handling procedures should be followed, as LED chips are sensitive to static electricity.

4. Application Suggestions

4.1 Typical Application Scenarios

This display is ideal for applications requiring a compact, reliable, and bright numeric readout. Common uses include:

• Test and Measurement Equipment: Digital multimeters, frequency counters, power supplies.
• Industrial Controls: Panel meters for temperature, pressure, RPM, count displays.
• Consumer Electronics: Audio equipment (amplifier volume/displays), kitchen appliances, clocks.
• Automotive Aftermarket: Gauges and display modules (where environmental specs are suitable).

4.2 Design Considerations & Circuit Implementation

Driving this display requires a multiplexing controller, which can be a dedicated display driver IC (like the MAX7219 or TM1637) or a microcontroller with sufficient I/O pins and software. The design must account for:

• Current Limiting: A resistor must be placed in series with each segment anode (or a set of anodes if using a constant-current driver) to set the forward current. The value is calculated using R = (Vcc - VF) / IF. Using the max VF of 2.6V and a 5V supply with a target IF of 10mA, R = (5 - 2.6) / 0.01 = 240 ohms.
• Multiplexing Frequency: The refresh rate must be high enough to avoid visible flicker, typically above 60-100 Hz per digit. With 4 digits, the scanning frequency needs to be 240-400 Hz.
• Peak Current vs. Average Current: To achieve a desired average brightness, the peak current during the short ON time can be higher. If the duty cycle is 1/4 (for 4 digits), a peak current of 20mA yields an average current of 5mA per segment, staying within the continuous rating.
• Heat Dissipation: Ensure the average power dissipation per segment (IF * VF * duty cycle) does not exceed 70mW, especially at high ambient temperatures.

5. Technical Comparison & Differentiation

The LTC-4727JD differentiates itself through its use of AlInGaP technology on a GaAs substrate. Compared to older GaP (Gallium Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in brighter displays at the same current or lower power consumption for the same brightness. The non-transparent substrate helps improve contrast by preventing internal light scattering. The \"continuous uniform segments\" feature indicates a high-quality die and lens design that avoids gaps or uneven illumination within a segment. The lead-free package ensures compliance with modern environmental regulations (RoHS).

6. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength is the physical point of highest spectral power output from the LED. Dominant wavelength is the perceived color point by the human eye, calculated from the full spectrum. They often differ slightly.

Q: Can I drive this display with a 3.3V microcontroller?
A: Yes, but you must check the forward voltage. With a VF of 2.6V max, there is only 0.7V headroom (3.3V - 2.6V) for the current-limiting resistor. This small voltage drop makes the current more sensitive to variations in VF. A constant-current driver is recommended for 3.3V systems, or use a lower target current.

Q: Why is there a derating factor for forward current?
A: LEDs generate heat at the semiconductor junction. As ambient temperature rises, the junction temperature increases for a given power dissipation. The derating factor lowers the maximum allowed current to prevent the junction temperature from exceeding its maximum rating, which would drastically reduce lifespan or cause failure.

Q: What does \"multiplex common cathode\" mean for my driver circuit?
A: It means you turn on one digit at a time by connecting its common cathode pin to ground (low). You then apply voltage to the segment anode pins for the pattern you want on that digit. You rapidly cycle through all digits. The human eye integrates the light, making all digits appear continuously lit.

7. Practical Implementation Case Study

Consider designing a simple 4-digit voltmeter using a microcontroller and this display. The microcontroller's ADC reads a voltage, converts it to a number, and drives the display. The microcontroller would have 8 I/O pins connected to the segment anodes (A-G, DP) via current-limiting resistors. Four additional I/O pins would control NPN transistors (or use a transistor array IC) that sink current from the four digit cathode pins (1, 2, 6, 8). Pin 4 (common cathode for colons) could be tied to ground if the colons are always on, or controlled separately. The firmware would implement a timer interrupt to refresh the display. In the interrupt routine, it would turn off all digit cathodes, output the segment pattern for the next digit to the anode port, and then turn on that digit's cathode. This process repeats for each digit, creating a stable, flicker-free readout.

8. Operating Principle Introduction

The fundamental operating principle is based on electroluminescence in a semiconductor P-N junction. When a forward voltage exceeding the diode's threshold is applied, electrons from the N-type AlInGaP region recombine with holes from the P-type region. This recombination event releases energy in the form of photons (light). The specific wavelength of 650 nm (red) is determined by the bandgap energy of the AlInGaP semiconductor material, which is engineered during the crystal growth process. The non-transparent GaAs substrate absorbs light emitted downwards, improving contrast. The individual segments are formed by multiple LED chips or a single chip with a patterned anode, wired internally to the package pins. The multiplexing scheme is an electrical technique to reduce the number of required control lines by taking advantage of the human eye's persistence of vision.

9. Technology Trends

While AlInGaP remains a high-performance technology for red and amber LEDs, the broader display industry trends impact such components. There is a continuous drive towards higher efficiency (more lumens per watt), allowing for brighter displays at lower power or reduced heat generation. Miniaturization is another trend, though digit height is often constrained by readability requirements. Integration is a significant trend; modern display modules often include the driver IC, controller, and sometimes even a microcontroller within the same package, simplifying the interface to a simple serial bus (I2C or SPI). However, discrete displays like the LTC-4727JD remain vital for cost-sensitive designs, custom layouts, or applications where the control electronics are centralized. The move towards lead-free and halogen-free materials in compliance with global environmental regulations is now standard. Future developments may see further efficiency gains from new substrate materials or chip designs, but the core multiplexed seven-segment architecture remains a reliable and cost-effective solution for numeric display needs.