LTP-4823JD 0.4-inch Dual Digit Alphanumeric LED Display Datasheet - 10mm Digit Height - Hyper Red (650nm) - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-4823JD is a compact, high-performance dual-digit alphanumeric display module designed for applications requiring clear character and symbol presentation. Its primary function is to provide a visual output interface for numeric data, letters, and specific symbols, making it suitable for a wide range of instrumentation, control panels, and consumer electronics.

The core advantage of this device lies in its utilization of AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor technology for the LED chips. This material system is renowned for producing high-efficiency red and amber LEDs. The chips are fabricated on a non-transparent GaAs substrate, which helps in improving contrast by minimizing internal light scattering and reflection. The display features a gray face with white segments, a combination that enhances readability and aesthetic appeal when the LEDs are off. The device is categorized for luminous intensity and is offered in a lead-free package compliant with RoHS (Restriction of Hazardous Substances) directives.

1.1 Key Features and Target Market

The display boasts several features that make it attractive for design engineers:

• Digit Height: 0.4 inches (10 mm), offering a good balance between size and visibility.
• Segment Quality: Continuous uniform segments ensure consistent illumination and a professional appearance.
• Power Efficiency: Low power requirement, contributing to energy-efficient system design.
• Optical Performance: High brightness and high contrast ratio ensure excellent visibility even in well-lit environments.
• Viewing Angle: A wide viewing angle allows for readability from various positions.
• Reliability: Solid-state construction offers long operational life and resistance to shock and vibration.

The target market includes industrial control systems, test and measurement equipment, medical devices, automotive dashboards (secondary displays), point-of-sale terminals, and household appliances where clear, reliable alphanumeric feedback is required.

2. Technical Specifications Deep Dive

2.1 Electrical and Optical Characteristics

The performance of the LTP-4823JD is defined under standard test conditions at an ambient temperature (Ta) of 25°C. Key parameters include:

• Average Luminous Intensity (I_V): Ranges from a minimum of 320 µcd to a maximum of 975 µcd at a forward current (I_F) of 1 mA. The typical value falls within this range. This parameter defines the brightness of each illuminated segment.
• Peak Emission Wavelength (λ_p): 650 nanometers (nm). This is the wavelength at which the LED emits the most optical power, defining its \"hyper red\" color.
• Dominant Wavelength (λ_d): 639 nm. This is the single wavelength perceived by the human eye, which may differ slightly from the peak wavelength.
• Spectral Line Half-Width (Δλ): 20 nm. This indicates the spectral purity or the spread of the emitted light around the peak wavelength.
• Forward Voltage per Segment (V_F): Typically 2.6 Volts, with a maximum of 2.6V at I_F=20mA. The minimum is 2.1V. This is crucial for designing the current-limiting circuitry.
• Reverse Current per Segment (I_R): Maximum 100 µA at a reverse voltage (V_R) of 5V.
• Luminous Intensity Matching Ratio: 2:1 maximum for segments within a similar light area at I_F=1mA. This specifies the maximum allowable brightness variation between segments to ensure uniform appearance.

Luminous intensity measurements are performed using a sensor and filter calibrated to approximate the CIE photopic eye-response curve, ensuring the values correlate with human visual perception.

2.2 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage may occur. Operation outside these limits is not guaranteed.

• Average Power Dissipation per Segment: 70 mW.
• Peak Forward Current per Segment: 90 mA (likely for pulsed operation).
• Average Forward Current per Segment: 25 mA at 25°C. This rating derates linearly by 0.33 mA/°C as ambient temperature increases above 25°C.
• Reverse Voltage per Segment: 5 V.
• Operating Temperature Range: -35°C to +105°C.
• Storage Temperature Range: -35°C to +105°C.

3. Mechanical and Package Information

3.1 Physical Dimensions and Tolerances

The package dimensions are provided in millimeters. Key tolerances include ±0.25 mm for most dimensions and ±0.4 mm for pin tip shift. Detailed dimensional drawings are essential for PCB (Printed Circuit Board) footprint design to ensure proper fit and alignment. The display is a through-hole device with pins designed for soldering.

3.2 Pin Connection and Internal Circuit

The LTP-4823JD is a 20-pin device configured as a common anode, duplex display. This means it has two independent digits (Character 1 and Character 2), each with a shared anode connection. The individual segment cathodes are brought out to separate pins.

Pinout Summary: Pins 4 and 10 are the common anodes for digit 1 and digit 2, respectively. The remaining pins (1-3, 5-9, 11-13, 15-20) are cathodes for the various segments (A, B, C, D, E, F, G, H, K, M, N, P, R, S, T, U, D.P.). Pin 14 is noted as \"No Connection\" (N/C). The internal circuit diagram shows the arrangement of these LEDs with their common anode connections.

This common anode configuration requires the driving circuit to source current to the common anode pin and sink current through the individual cathode pins to illuminate a specific segment.

4. Soldering and Assembly Guidelines

The datasheet specifies soldering conditions to prevent thermal damage during assembly. The recommended condition is soldering at 260°C for a maximum of 3 seconds, measured at a point 1/16 inch (approximately 1.6 mm) below the seating plane of the package. It is critical not to exceed the maximum temperature ratings of the device during any part of the assembly process. Proper ESD (Electrostatic Discharge) handling procedures should always be followed for LED components.

5. Application Suggestions and Design Considerations

5.1 Typical Application Circuits

To drive the LTP-4823JD, a multiplexing scheme is typically employed due to its common anode configuration. A microcontroller or dedicated display driver IC is used. The common anodes (pins 4 and 10) are connected to current-source outputs or switched power via transistors. The segment cathode pins are connected to current-sink drivers (like a transistor array or driver IC with open-collector/drain outputs).

The display is multiplexed by rapidly switching (strobing) the power to each digit's common anode while presenting the corresponding segment data on the cathode lines. A refresh rate high enough to avoid visible flicker (typically >60 Hz per digit) must be maintained. Current-limiting resistors are mandatory for each segment cathode (or possibly for each common anode, depending on the driver design) to set the desired forward current, typically between 1 mA and 20 mA as per the application's brightness requirement.

5.2 Design Considerations

• Current Limiting: Always use series resistors to control the segment current. Calculate the resistor value using R = (V_supply - V_F) / I_F, where V_F is the forward voltage from the datasheet (use max value for a safe design).
• Power Dissipation: Ensure the average current per segment does not exceed the rated 25 mA, considering derating with temperature. The total power for all illuminated segments must be managed.
• Viewing Conditions: The high contrast and wide viewing angle make it suitable for applications where the display may be viewed from an angle. The gray face reduces ambient light reflection.
• Dimming: Brightness can be controlled via pulse-width modulation (PWM) of the drive current, which is more effective and color-stable than analog current reduction.

6. Performance Curve Analysis

The datasheet references typical electrical and optical characteristic curves. While the specific graphs are not detailed in the provided text, such curves generally include:

• Relative Luminous Intensity vs. Forward Current (I_V vs. I_F): Shows how brightness increases with current, typically in a sub-linear fashion, highlighting the point of diminishing returns.
• Forward Voltage vs. Forward Current (V_F vs. I_F): Demonstrates the diode's exponential I-V characteristic.
• Relative Luminous Intensity vs. Ambient Temperature (I_V vs. T_a): Illustrates how LED output decreases as junction temperature rises, emphasizing the importance of thermal management in high-brightness or high-temperature applications.
• Spectral Distribution: A graph showing the intensity of emitted light across different wavelengths, centered around 650 nm with a ~20 nm half-width.

These curves are vital for understanding the device's behavior under non-standard conditions and for optimizing the drive circuitry for efficiency and longevity.

7. Technical Comparison and Differentiation

The LTP-4823JD differentiates itself through its AlInGaP technology. Compared to older technologies like standard GaAsP (Gallium Arsenide Phosphide) red LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in greater brightness for the same drive current or lower power consumption for the same brightness. The \"hyper red\" color (650nm) is often more visually striking and can have better performance in some optical sensor systems. The 16-segment format provides alphanumeric capability beyond simple 7-segment numeric displays, while the dual-digit, single-module construction saves board space compared to two separate single-digit units.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the difference between peak wavelength (650nm) and dominant wavelength (639nm)?
A: Peak wavelength is the physical peak of the emission spectrum. Dominant wavelength is the perceived color point. The slight difference is due to the shape of the emission spectrum and the human eye's sensitivity curve (CIE). The dominant wavelength is more relevant for color specification.

Q: Can I drive this display with a 5V microcontroller without other components?
A: No. You must use external current-limiting resistors for each segment cathode. Connecting an LED directly to a microcontroller pin can damage both the LED (from overcurrent) and the microcontroller pin (from exceeding its current sink/source capability).

Q: What does \"categorized for luminous intensity\" mean?
A: It means the displays are tested and binned according to their measured brightness at a standard test current. This allows designers to select parts with consistent brightness levels for their application, ensuring uniform appearance across multiple units in a product.

Q: How do I achieve decimal point control?
A: The decimal point (D.P.) is a separate segment with its own cathode connection (Pin 5). It is controlled independently just like any other segment (A, B, C, etc.).

9. Operating Principle and Technology Trends

9.1 Basic Operating Principle

An LED is a semiconductor diode. When a forward voltage exceeding its bandgap voltage is applied, electrons and holes recombine in the active region of the semiconductor, releasing energy in the form of photons (light). The color of the light is determined by the energy bandgap of the semiconductor material. AlInGaP has a bandgap corresponding to red/orange/amber light. The non-transparent substrate helps direct more of the generated light out of the top of the device, improving efficiency.

9.2 Industry Trends

The trend in alphanumeric displays is towards higher integration, surface-mount technology (SMT) packages for automated assembly, and sometimes the inclusion of the driver IC within the display module itself. While through-hole displays like the LTP-4823JD remain popular for prototyping, repair-friendly designs, and certain industrial applications, SMT versions are becoming more prevalent in high-volume consumer electronics. Furthermore, there is a constant drive for higher efficiency (more light per watt) and improved reliability across wider temperature ranges.