LTP-537JD LED Display Datasheet - 0.5-inch Digit Height - Hyper Red Color - 2.6V Forward Voltage - 70mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-537JD is a high-performance, single-digit alphanumeric display module designed for applications requiring clear, bright numeric and limited alphabetic character representation. Its core function is to provide visual output through individually addressable segments that form characters. The device is engineered with a focus on reliability and optical performance in industrial, instrumentation, and consumer electronic interfaces.

The display utilizes advanced AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for its light-emitting elements. This material technology is specifically chosen for its efficiency in producing high-brightness red light. The chips are fabricated on a non-transparent GaAs (Gallium Arsenide) substrate, which enhances contrast by preventing internal light scattering and reflection, directing more emitted light forward through the segments. The visual presentation features a black faceplate, which significantly increases the contrast ratio by absorbing ambient light, combined with white segment areas that allow the emitted red light to pass through, resulting in sharp, well-defined characters against a dark background.

1.1 Core Advantages and Target Market

The primary advantages of this display stem from its optoelectronic design and construction. The use of AlInGaP LEDs provides high luminous intensity and excellent efficiency in the red spectrum. The black face and white segment design is a critical feature for achieving high contrast, making the display easily readable under various lighting conditions, including bright ambient light. The continuous uniform segments ensure a consistent and professional appearance of the formed characters, without visible gaps or irregularities in the lit areas.

The device is categorized for luminous intensity, meaning units are binned or tested to ensure they meet specific brightness thresholds, providing consistency in production runs. Its wide viewing angle ensures legibility from off-axis positions, which is crucial for panel-mounted equipment. The low power requirement per segment makes it suitable for battery-powered or energy-conscious applications. Finally, its solid-state reliability implies a long operational lifetime with no moving parts, resistant to shock and vibration.

The target market for this component includes industrial control panels, test and measurement equipment, medical devices, automotive dashboards (for auxiliary displays), point-of-sale systems, and household appliances where a single-digit readout is required for settings, counters, or status indicators.

2. In-Depth Technical Parameter Analysis

The electrical and optical parameters define the operating boundaries and performance characteristics of the display. Understanding these is essential for proper circuit design and integration.

2.1 Absolute Maximum Ratings

These ratings specify the limits beyond which permanent damage to the device may occur. They are not conditions for normal operation.

• Power Dissipation per Segment: 70 mW. This is the maximum allowable power that can be dissipated as heat by a single LED segment under any condition. Exceeding this can lead to overheating and accelerated degradation or failure.
• Peak Forward Current per Segment: 90 mA. This is allowed only under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width. It is useful for multiplexing schemes or achieving momentary higher brightness.
• Continuous Forward Current per Segment: 25 mA at 25°C. This is the recommended maximum current for constant operation. A derating factor of 0.33 mA/°C is specified, meaning the maximum allowable continuous current decreases linearly as the ambient temperature (Ta) rises above 25°C to prevent thermal overstress.
• Reverse Voltage per Segment: 5 V. Applying a reverse bias voltage higher than this can break down the LED's PN junction.
• Operating and Storage Temperature Range: -35°C to +85°C. The device is rated to function and be stored within this broad temperature range, suitable for most non-extreme environments.
• Solder Temperature: 260°C for 3 seconds at 1/16 inch (approximately 1.6 mm) below the seating plane. This provides guidelines for wave or reflow soldering processes to avoid damaging the plastic package or internal bonds.

2.2 Electrical & Optical Characteristics

These are the typical and maximum/minimum values under specified test conditions (usually at Ta=25°C). They describe the device's performance during normal operation.

• Average Luminous Intensity (I_V): 320 μcd (Min), 700 μcd (Typ) at I_F=1mA. This is a measure of the light output. The categorization mentioned in the features likely groups devices based on this parameter (e.g., standard and high-brightness bins).
• Peak Emission Wavelength (λ_p): 650 nm (Typ) at I_F=20mA. This is the wavelength at which the spectral output is strongest, placing it in the hyper-red region of the visible spectrum.
• Dominant Wavelength (λ_d): 639 nm (Typ) at I_F=20mA. This is the single wavelength perceived by the human eye, defining the color. The difference between peak and dominant wavelength is due to the shape of the emission spectrum.
• Spectral Line Half-Width (Δλ): 20 nm (Typ) at I_F=20mA. This indicates the spectral purity; a smaller value means a more monochromatic light. 20 nm is typical for AlInGaP red LEDs.
• Forward Voltage per Segment (V_F): 2.1V (Min), 2.6V (Typ) at I_F=20mA. This is the voltage drop across the LED when conducting. It is crucial for designing the current-limiting circuitry. The driver supply voltage must be higher than this value.
• Reverse Current per Segment (I_R): 100 μA (Max) at V_R=5V. This is the small leakage current that flows when the LED is reverse-biased within 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 when driven under the same conditions (I_F=1mA). A ratio of 2:1 ensures reasonable uniformity in appearance.

Measurement Note: Luminous intensity is measured using a sensor and filter that approximate the CIE photopic eye-response curve, ensuring the values correspond to human visual perception.

3. Binning System Explanation

The datasheet indicates the product is \"categorized for luminous intensity.\" This implies a binning or sorting process.

• Luminous Intensity Binning: Post-manufacturing, individual displays are tested for their light output at a standard current (likely 1mA or 20mA). They are then grouped into different bins or categories based on their measured I_V. For example, one bin may contain devices with I_V between 320-500 μcd, and a premium bin may contain devices from 500-700 μcd. This allows customers to select a consistency level suitable for their application, ensuring uniform brightness across multiple digits in a system. The datasheet provides the overall min/typ range, but specific bin codes would typically be part of the full ordering information.

4. Performance Curve Analysis

While the specific graphs are not detailed in the provided text, typical curves for such a device would include:

• Current vs. Forward Voltage (I-V Curve): Shows the exponential relationship. The forward voltage (V_F) increases with current (I_F). The curve is temperature-dependent, with V_F decreasing as junction temperature rises for a given current.
• Luminous Intensity vs. Forward Current (I_V vs. I_F): Generally shows a linear or slightly sub-linear increase in light output with increasing current up to a point, after which efficiency drops due to thermal effects.
• Luminous Intensity vs. Ambient Temperature: Shows how light output decreases as the ambient (and thus junction) temperature increases. AlInGaP LEDs have a relatively strong negative temperature coefficient for light output.
• Spectral Distribution: A plot of relative intensity vs. wavelength, showing a peak around 650 nm and a half-width of about 20 nm, confirming the hyper-red color.

These curves are essential for designing drivers that compensate for temperature changes and for understanding brightness behavior under different operating conditions.

5. Mechanical and Packaging Information

5.1 Package Dimensions and Mounting

The device features a standard LED display package. Key dimensional notes from the datasheet include that all dimensions are in millimeters, with standard tolerances of ±0.25 mm (0.01\") unless otherwise specified. The exact footprint, lead spacing, digit height (12.7mm), and overall package size are defined in the dimension drawing, which is critical for PCB (Printed Circuit Board) layout to ensure proper fit and alignment in the cutout.

5.2 Pin Connection and Polarity

The LTP-537JD is a common cathode display. This means all 18 segments (16 character segments plus a right-hand decimal point) share a common negative connection (Cathode) on Pin 18. Each individual segment has its own dedicated anode pin (Pins 1-17). This configuration is common and simplifies multiplexing driver circuits, where the common cathode is switched to ground while the desired anodes are driven high through current-limiting resistors.

The pinout explicitly lists the connection for each pin, mapping physical pin numbers to segment functions (A, B, C, D, E, F, G, H, K, M, N, P, R, S, T, U, and D.P. for decimal point). An internal circuit diagram would typically show this common cathode arrangement.

6. Soldering and Assembly Guidelines

The primary guideline provided is for the soldering process itself: 260°C for 3 seconds, measured at a point 1/16 inch (1.6 mm) below the seating plane of the package. This is a standard reflow profile parameter. It is crucial to adhere to this to prevent:

• Thermal damage to the plastic epoxy of the package, which can cause discoloration or cracking.
• Overheating the internal wire bonds connecting the LED chips to the leads.
• Exposing the semiconductor die to excessive temperature.

General handling precautions should also be observed: avoid mechanical stress on the leads, use ESD (Electrostatic Discharge) precautions during handling, and store in appropriate anti-static, dry conditions within the specified -35°C to +85°C storage range.

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuits

The most common drive method is multiplexing. Since it is a common-cathode device, a microcontroller or dedicated driver IC can sink current through the common cathode pin (Pin 18) while sourcing current to the specific anode pins for the segments that need to be lit. Multiple digits can be multiplexed by rapidly cycling which digit's cathode is active while presenting the corresponding segment data on the shared anode lines. This greatly reduces the number of required microcontroller I/O pins.

A current-limiting resistor is mandatory for each anode line (or a current-regulated driver). The resistor value is calculated using Ohm's Law: R = (V_supply - V_F) / I_F. Using the typical V_F of 2.6V at 20mA and a 5V supply: R = (5V - 2.6V) / 0.020A = 120 Ohms. A standard 120Ω resistor would be used. The power rating of the resistor should be checked: P = I² * R = (0.02)² * 120 = 0.048W, so a standard 1/8W (0.125W) resistor is sufficient.

7.2 Design Considerations

• Heat Management: While individual segments dissipate little power (max 70mW), the collective heat from multiple lit segments or operation at high ambient temperature must be considered. Ensure adequate ventilation and consider the current derating above 25°C.
• Viewing Angle and Contrast: The wide viewing angle and high-contrast design make it suitable for panels where the user may not be directly in front of the device. The black face is particularly beneficial in high-ambient-light environments.
• Software for Character Generation: A lookup table in the driving microcontroller's firmware is needed to map alphanumeric characters (e.g., '0'-'9', 'A', 'C', 'E', 'F') to the correct combination of the 16 segments.

8. Frequently Asked Questions (Based on Technical Parameters)

Q1: Can I drive this display directly from a 3.3V microcontroller pin?
A: Possibly, but with reduced brightness. The typical V_F is 2.6V. At 3.3V supply, the voltage headroom for the current-limiting resistor is only 0.7V (3.3V - 2.6V). To achieve 20mA, you would need a 35Ω resistor (0.7V / 0.02A). However, the actual V_F can be as low as 2.1V, which would result in a higher current with the same resistor, potentially exceeding limits. A constant-current driver or careful characterization is recommended for 3.3V systems.

Q2: What is the difference between \"peak\" and \"dominant\" wavelength?
A: Peak wavelength is the physical peak of the light emission spectrum. Dominant wavelength is the single wavelength of pure monochromatic light that would appear to have the same color as the LED's output to the human eye. Due to the spectral shape, they often differ slightly.

Q3: How do I achieve the maximum brightness?
A: Operate at the maximum continuous current rating of 25mA per segment (at 25°C ambient), ensuring proper heat dissipation. Do not exceed the 70mW power dissipation limit. For short pulses, you could use the 90mA peak current under the specified duty cycle.

Q4: Why is there a luminous intensity matching ratio?
A: Manufacturing variations cause slight differences in light output between segments even at the same current. The 2:1 ratio guarantees that within one unit, no segment will be more than twice as bright as another, ensuring visual uniformity of the character.

9. Technology Introduction and Trends

9.1 AlInGaP LED Technology

The LTP-537JD uses AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for its LED chips. This material system is particularly efficient for producing light in the amber, red, and hyper-red wavelengths (roughly 590-650 nm). Compared to older technologies like GaAsP (Gallium Arsenide Phosphide), AlInGaP offers significantly higher luminous efficacy (more light output per electrical watt), better temperature stability, and longer lifetime. The growth of the epitaxial layers on a non-transparent GaAs substrate, as used here, is a common approach that improves light extraction efficiency by reflecting emitted light that would otherwise be lost into the substrate back out through the top of the chip.

9.2 Display Technology Context and Trends

While multi-digit dot-matrix OLED and LCD displays are now common for complex graphics, segmented LED displays like the LTP-537JD remain highly relevant for applications requiring extreme reliability, wide temperature range operation, high brightness, simplicity, and low cost for displaying fixed-format numbers and simple letters. The trend in such displays is not necessarily towards higher resolution but towards improved efficiency (lower operating current for the same brightness), enhanced contrast ratios, wider viewing angles, and sometimes the integration of driver electronics within the package. The fundamental principle of electroluminescence in a semiconductor PN junction remains unchanged, but material science and packaging techniques continue to advance their performance.