LTP-1557AKR LED Display Datasheet - 1.2 Inch (30.42mm) Matrix Height - AlInGaP Super Red - 5x7 Dot Array - English Technical Document

1. Product Overview

The LTP-1557AKR is a single-digit, alphanumeric display module designed for applications requiring clear, reliable character output. Its core component is a 5 column by 7 row (5x7) array of light-emitting diodes (LEDs), providing the standard resolution for displaying ASCII and EBCDIC characters. The physical display area features a 1.2-inch (30.42 mm) matrix height, offering good readability. The device is constructed with a gray face and white dot color scheme, which enhances contrast and legibility under various lighting conditions.

The primary technology behind the light emission is AlInGaP (Aluminum Indium Gallium Phosphide) Super Red LED chips. These chips are fabricated on a non-transparent Gallium Arsenide (GaAs) substrate. AlInGaP technology is known for its high efficiency and excellent color purity in the red-orange-yellow spectrum, making this display suitable for applications where vibrant red output is desired.

A key operational feature is its X-Y select architecture. Instead of individually addressing each of the 35 dots, the display uses a matrix configuration where anodes are connected in rows and cathodes are connected in columns (or vice-versa). This significantly reduces the number of required driver pins from 35 to 12 (5 rows + 7 columns), simplifying interface circuitry and controller requirements. The device is also designed to be stackable horizontally, allowing for the creation of multi-character displays by placing multiple units side-by-side.

1.1 Core Advantages and Target Market

The display offers several distinct advantages for system designers. Its low power requirement makes it suitable for battery-powered or energy-conscious devices. The solid-state reliability of LEDs, with no moving parts and high resistance to shock and vibration, ensures long operational life. The wide viewing angle and single-plane design provide consistent visibility from different perspectives. Furthermore, the device is categorized for luminous intensity, meaning units are binned and sold according to specific brightness ranges, allowing for consistency in multi-display applications or when brightness matching is critical.

The primary target markets for this display include industrial instrumentation, test and measurement equipment, point-of-sale terminals, legacy computer interfaces, and any embedded system requiring a simple, durable, and bright character readout. Its compatibility with standard character codes allows for easy integration with microcontrollers and digital systems.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Optical Characteristics

The optical performance is defined under specific test conditions at an ambient temperature (Ta) of 25\u00b0C. The key parameter is the Average Luminous Intensity (I_V), which has a typical value of 3800 \u00b5cd (microcandelas) and a minimum of 2100 \u00b5cd when driven at a peak current (I_p) of 80mA with a 1/16 duty cycle. This measurement approximates the CIE photopic eye-response curve, ensuring the value correlates with perceived brightness.

The color characteristics are defined by wavelength. The Peak Emission Wavelength (\u03bb_p) is typically 639 nm, placing it in the bright red portion of the spectrum. The Dominant Wavelength (\u03bb_d) is typically 631 nm. The difference between peak and dominant wavelength is normal for LEDs and relates to the shape of the emission spectrum. The Spectral Line Half-Width (\u0394\u03bb) is typically 20 nm, indicating the spectral purity or the range of wavelengths emitted around the peak.

A critical specification for ensuring uniform appearance is the Luminous Intensity Matching Ratio (I_V-m), which is 2:1 maximum. This means the brightest dot in the array will be no more than twice as bright as the dimmest dot under the same driving conditions, which is acceptable for character readability.

2.2 Electrical Characteristics

The forward voltage (V_F) for any single LED dot, measured at a forward current (I_F) of 20mA, ranges from a minimum of 2.0V to a maximum of 2.6V, with a typical value implied within this range. This is the voltage drop across the LED when illuminated. The reverse current (I_R) is specified as a maximum of 100 \u00b5A when a reverse voltage (V_R) of 5V is applied, indicating the device's leakage characteristics in the off-state.

2.3 Absolute Maximum Ratings and Thermal Considerations

These ratings define the limits beyond which permanent damage may occur. The Average Power Dissipation per Dot must not exceed 33 mW. The Peak Forward Current per Dot is rated at 90 mA, but only under specific pulsed conditions: a 1/10 duty cycle and a 0.1 ms pulse width. The Average Forward Current per Dot has a base rating of 13 mA at 25\u00b0C and derates linearly at a rate of 0.17 mA/\u00b0C as temperature increases above 25\u00b0C. This derating is crucial for thermal management and long-term reliability.

The maximum Reverse Voltage per Dot is 5V. The device is rated for an Operating Temperature Range of -35\u00b0C to +85\u00b0C and a similar Storage Temperature Range. For assembly, the solder temperature must not exceed 260\u00b0C for more than 3 seconds, measured at a point 1.6mm below the seating plane of the component.

3. Binning System Explanation

The datasheet explicitly states the device is categorized for luminous intensity. This is a binning process where manufactured units are tested and sorted into groups based on their measured light output under standard conditions. This allows customers to select parts with guaranteed minimum brightness or to ensure consistency across all displays in a product, preventing one character from appearing noticeably dimmer than another in a multi-unit setup. While the datasheet provides the full range (2100-3800 \u00b5cd min/typ), ordered parts would typically fall into a narrower, specified bin.

4. Performance Curve Analysis

The datasheet references Typical Electrical/Optical Characteristic Curves. While the specific curves are not detailed in the provided text, such curves in LED datasheets typically include:

• Forward Current vs. Forward Voltage (I_F-V_F Curve): Shows the non-linear relationship between current and voltage, essential for designing current-limiting circuitry.
• Luminous Intensity vs. Forward Current (I_V-I_F Curve): Demonstrates how light output increases with current, usually in a linear region before efficiency drops at very high currents.
• Luminous Intensity vs. Ambient Temperature (I_V-T_a Curve): Shows the decrease in light output as the junction temperature rises, highlighting the importance of thermal management.
• Spectral Distribution Curve: A graph plotting relative intensity against wavelength, visually defining the peak (\u03bb_p) and half-width (\u0394\u03bb).

These curves are vital for understanding the device's behavior under non-standard conditions and for optimizing drive parameters for specific application needs.

5. Mechanical and Package Information

The device comes in a standard LED display package. The Package Dimensions drawing provides all critical mechanical outlines, though the exact dimensions are not listed in the text. Tolerances are generally \u00b10.25 mm unless otherwise specified. The drawing would include overall length, width, and height, lead spacing, and the position of the display window.

5.1 Pin Connection and Internal Circuit

The display has a 14-pin interface. The pinout is as follows: Pin 1: Anode Row 5; Pin 2: Anode Row 7; Pin 3: Cathode Column 2; Pin 4: Cathode Column 3; Pin 5: Anode Row 4; Pin 6: Cathode Column 5; Pin 7: Anode Row 6; Pin 8: Anode Row 3; Pin 9: Anode Row 1; Pin 10: Cathode Column 4; Pin 11: Cathode Column 3 (Note: Column 3 appears on two pins, 4 and 11, which may be internally connected or a documentation error requiring verification); Pin 12: Anode Row 4 (Note: Row 4 appears on pins 5 and 12); Pin 13: Cathode Column 1; Pin 14: Anode Row 2.

The Internal Circuit Diagram would visually represent the 5x7 matrix, showing how the 5 row anodes and 7 column cathodes interconnect the 35 individual LED dots. This diagram is essential for understanding the multiplexing drive sequence.

6. Soldering and Assembly Guidelines

The key assembly specification is the soldering profile. The device can withstand a maximum solder temperature of 260\u00b0C for a maximum of 3 seconds. This measurement is taken at a point 1.6mm (1/16 inch) below the seating plane of the package body. This guideline is critical for wave soldering or reflow processes to prevent thermal damage to the LED chips or internal bonds. Standard ESD (Electrostatic Discharge) precautions should be observed during handling. For storage, the specified range of -35\u00b0C to +85\u00b0C in a dry environment should be maintained.

7. Application Suggestions

7.1 Typical Application Scenarios

This display is ideal for any application requiring a single, bright, alphanumeric readout. Examples include: digital panel meters for voltage, current, or temperature; setting displays on industrial controllers; status indicators on network or telecom equipment; scoreboards or timers; and diagnostic displays on medical or test equipment.

7.2 Design Considerations

• Drive Circuitry: A microcontroller with sufficient I/O pins or a dedicated LED display driver IC (like a MAX7219 or similar) is required to perform the multiplexing. The driver must sink/source the necessary peak current (up to 80mA per dot pulsed, but average current is much lower due to duty cycle).
• Current Limiting: External current-limiting resistors are mandatory for each anode row or cathode column (depending on the drive configuration) to set the forward current and protect the LEDs.
• Multiplexing Timing: The refresh rate and duty cycle must be high enough to avoid visible flicker. A 1/16 duty cycle, as used in the test condition, is common. The peak current must be adjusted so that the average current and power dissipation per dot remain within limits.
• Thermal Management: Ensure the average current is derated appropriately if the operating ambient temperature is expected to exceed 25\u00b0C significantly. Adequate PCB copper or airflow may be necessary.
• Optical Interface: Consider the need for filters, diffusers, or protective windows in the end-product design.

8. Technical Comparison and Differentiation

Compared to older technologies like incandescent or vacuum fluorescent displays (VFDs), this LED display offers superior shock/vibration resistance, lower operating voltage, faster response time, and potentially longer lifetime. Compared to modern graphic OLEDs or LCDs, it is simpler, more robust in harsh environments, offers superior brightness and viewing angle, and requires less complex control electronics, though it is limited to pre-defined character shapes.

Within the LED display family, the use of AlInGaP Super Red technology differentiates it from standard GaAsP or GaP red LEDs by offering higher efficiency and better color saturation. The specific 1.2-inch height and 5x7 format make it a standard replacement part for many legacy systems.

9. Frequently Asked Questions Based on Technical Parameters

Q: Can I drive this display with a constant DC current on each dot?
A: Technically yes, but it would require 35 independent drivers, which is impractical. The matrix design is intended for multiplexed (X-Y) driving to minimize pin count.

Q: Why is the peak current (90mA) so much higher than the average current rating (13mA)?
A: Because the display is multiplexed, each dot is only powered for a fraction of the time (duty cycle). The peak current during its brief "on" time can be higher to achieve the desired brightness, as long as the average current over time stays within the 13mA limit to prevent overheating.

Q: What does a 2:1 intensity matching ratio mean for my application?
A: It means some variation in dot brightness is normal. For character displays, this minor variation is usually not perceptible to the eye and does not affect readability. For applications requiring perfect uniformity, selecting parts from a tighter bin or using optical diffusers may be necessary.

Q: How do I calculate the required current-limiting resistor value?
A: You need the supply voltage (V_CC), the desired forward current (I_F), and the LED forward voltage (V_F). Use Ohm's Law: R = (V_CC - V_F) / I_F. Remember I_F here is the peak current during the dot's active time in the multiplex cycle.

10. Practical Use Case Example

Consider designing a simple digital thermometer. A microcontroller reads a temperature sensor, performs a calculation, and needs to display a 3-digit value (e.g., " 23.5"). Three LTP-1557AKR displays could be stacked horizontally. The microcontroller, using a display driver IC, would multiplex the three displays. It would convert the numerical value into the corresponding 5x7 font patterns for digits, decimal point, and degree symbol. The driver IC would sequentially activate the correct rows and columns for each display at a high speed, creating the illusion of a stable, continuously lit readout. The AlInGaP red LEDs would ensure the reading is clearly visible even in brightly lit environments.

11. Operating Principle Introduction

The display operates on the principle of LED matrix multiplexing. Internally, 35 discrete LEDs are arranged in a grid. All LED anodes in a given row are connected together, and all cathodes in a given column are connected together. To illuminate a specific dot at the intersection of Row X and Column Y, a positive voltage is applied to Row X while Column Y is connected to ground (for common-cathode configuration, which this appears to be based on the pinout). By rapidly scanning through each row and activating the appropriate columns for that row's pattern, all dots in the desired character shape can be illuminated in a sequence that the human eye perceives as a steady image. This method reduces the number of control lines from 35 to 12.

12. Technology Trends and Context

Displays like the LTP-1557AKR represent a mature, reliable technology. While high-resolution dot matrix and graphic OLED/LCD displays dominate modern user interfaces, discrete LED character displays remain relevant in specific niches. Their advantages are unwavering: extreme durability, wide operating temperature range, high brightness, low cost for simple tasks, and simplicity of interface. The trend within this niche is towards higher efficiency LEDs (like the AlInGaP used here), surface-mount packages for automated assembly, and integration with simpler controller interfaces (e.g., I2C or SPI). They are unlikely to be replaced in applications where environmental robustness and long-term reliability under harsh conditions are the primary concerns over graphical flexibility.