LTP-2157AKY LED Display Datasheet - 2.0-inch (50.8mm) Matrix Height - AlInGaP Amber Yellow - 2.6V Forward Voltage - 35mW Power Dissipation - English Technical Document

1. Product Overview

The LTP-2157AKY is a 2.0-inch (50.8 mm) character height, 5 x 7 dot matrix LED display module. This device is designed for applications requiring clear, bright alphanumeric or symbolic information display. Its core technology utilizes AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material to produce an amber yellow light emission. The visual presentation features a gray faceplate with white dot color, enhancing contrast and readability. The module is constructed as a common-cathode array, requiring external multiplexing drive circuitry for operation.

The primary application domains for this display include industrial instrumentation, consumer electronics interfaces, point-of-sale terminals, medical equipment displays, and any embedded system requiring a compact, reliable, and bright readout. Its solid-state construction ensures high reliability and long operational life compared to other display technologies like vacuum fluorescent or incandescent types.

1.1 Core Advantages and Target Market

The key advantages of the LTP-2157AKY stem from its AlInGaP LED technology and thoughtful design. It offers high brightness and high contrast, which are critical for readability under various ambient lighting conditions, including brightly lit indoor environments. The low power requirement makes it suitable for battery-powered or energy-conscious applications. The excellent character appearance is achieved through the precise 5x7 dot matrix layout, which is the standard for displaying ASCII characters clearly.

The target market is broad, encompassing OEMs (Original Equipment Manufacturers) and design engineers working on devices that need a simple, cost-effective, and robust display solution. Its specifications make it a viable choice where larger, more complex graphic displays are unnecessary or too expensive.

2. In-Depth Technical Parameter Analysis

A thorough understanding of the electrical and optical parameters is essential for proper circuit design and integration of the LTP-2157AKY display.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operating the device continuously at or near these limits is not recommended.

• Average Power Dissipation Per Dot: 35 mW. This is the maximum continuous power that can be safely dissipated by a single LED segment (dot) without causing thermal degradation.
• Peak Forward Current Per Dot: 60 mA. This is the maximum instantaneous current allowed during pulsed operation, typically used in multiplexed driving schemes.
• Average Forward Current Per Dot: 13 mA at 25°C. This rating derates linearly at 0.17 mA/°C above 25°C. For example, at 85°C, the maximum allowable average current would be approximately: 13 mA - (0.17 mA/°C * (85°C - 25°C)) = 13 mA - 10.2 mA = 2.8 mA. This derating is crucial for thermal management.
• Reverse Voltage Per Dot: 5 V. Exceeding this voltage in reverse bias can break down the LED junction.
• Operating & Storage Temperature Range: -35°C to +85°C. This wide range ensures functionality in harsh environments.
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane. This is a standard wave or reflow soldering guideline to prevent package damage.

2.2 Electrical & Optical Characteristics

These are the typical operating parameters measured at an ambient temperature (Ta) of 25°C under specified test conditions.

• Average Luminous Intensity (I_V): 2100 μcd (Min), 3600 μcd (Typ). Test Condition: I_p=32mA, 1/16 Duty cycle. This high brightness is a key feature. The measurement uses a filter approximating the CIE photopic eye-response curve for accuracy.
• Peak Emission Wavelength (λ_p): 595 nm (Typ). This is the wavelength at which the optical power output is maximum, defining the amber yellow color.
• Spectral Line Half-Width (Δλ): 15 nm (Typ). This indicates the spectral purity; a narrower width means a more monochromatic color.
• Dominant Wavelength (λ_d): 592 nm (Typ). This is the wavelength perceived by the human eye, closely matching the peak wavelength for this LED type.
• Forward Voltage Per Segment (V_F): 2.05V (Min), 2.6V (Typ). Test Condition: I_F=20mA. Designers must ensure the driving circuit can provide this voltage.
• Reverse Current (I_R): 100 μA (Max). Test Condition: V_R=5V. This is the leakage current when the LED is reverse-biased.
• Luminous Intensity Matching Ratio (I_V-m): 2:1 (Max). Test Condition: I_F=2mA. This parameter ensures uniformity across the display; the brightness of the dimmest segment will be at least half that of the brightest segment.

3. Binning System Explanation

The datasheet does not explicitly detail a multi-level binning system for wavelength or flux. However, the specified parameters imply a controlled manufacturing process. The tight ranges for Dominant Wavelength (592 nm Typ) and Luminous Intensity (2100-3600 μcd) suggest that parts are selected to meet these minimum and typical specifications. Designers should consider the minimum values (I_V min 2100 μcd, V_F max 2.6V) for worst-case circuit design to ensure display visibility and proper current regulation across all units.

4. Performance Curve Analysis

The datasheet references typical characteristic curves. While not provided in the text, standard LED curves can be inferred and are critical for design.

4.1 Forward Current vs. Forward Voltage (I-V Curve)

The I-V relationship is non-linear. The typical V_F of 2.6V at 20mA is the key design point. The curve shows a sharp turn-on around the LED's bandgap voltage (~2V for AlInGaP), after which current increases exponentially with voltage. Therefore, driving LEDs with a constant current source is strongly recommended over a constant voltage source to prevent thermal runaway and ensure consistent brightness.

4.2 Luminous Intensity vs. Forward Current

Luminous intensity is approximately proportional to forward current in the normal operating range (e.g., up to the rated average current). However, efficiency may drop at very high currents due to heating. The specified intensity at 32mA pulsed operation is optimized for multiplexed displays.

4.3 Temperature Dependence

LED characteristics are temperature-sensitive. Forward voltage (V_F) typically decreases with increasing junction temperature (negative temperature coefficient). Luminous intensity also decreases as temperature rises. The current derating specification (0.17 mA/°C) is a direct design guard against these effects, preventing overheating and premature brightness degradation.

4.4 Spectral Distribution

The emission spectrum is centered around 595 nm (amber yellow) with a typical half-width of 15 nm. This is a relatively narrow band, characteristic of direct-bandgap III-V semiconductors like AlInGaP, resulting in good color saturation.

5. Mechanical & Package Information

5.1 Physical Dimensions

The package drawing indicates the overall physical size of the display module. All dimensions are in millimeters with a standard tolerance of ±0.25 mm unless otherwise noted. This information is vital for PCB (Printed Circuit Board) footprint design and enclosure fitting.

5.2 Pin Configuration and Internal Circuit

The LTP-2157AKY has a 14-pin configuration. The internal circuit diagram shows a common-cathode arrangement for the 5x7 matrix. The columns (vertical lines) are the cathodes, and the rows (horizontal lines) are the anodes. Specific notes indicate internal connections: Pin 4 & Pin 11 are connected (both are Cathode for Column 3), and Pin 5 & Pin 12 are connected (both are Anode for Row 4). This internal connection likely simplifies the internal bonding wire layout. The pinout table must be followed precisely for correct display operation.

5.3 Polarity Identification

The device uses a common-cathode configuration. The cathode pins are for columns (1-5), and the anode pins are for rows (1-7). Applying forward bias requires connecting the desired row pin to a positive voltage (through a current-limiting resistor or driver) and the desired column pin to ground (or a low-side driver sink).

6. Soldering & Assembly Guidelines

The absolute maximum rating specifies the soldering profile: a maximum temperature of 260°C for a maximum duration of 3 seconds, measured 1.6mm (1/16 inch) below the seating plane. This is compatible with standard lead-free reflow soldering processes (e.g., following a standard IPC/JEDEC J-STD-020 profile). Care should be taken to avoid mechanical stress on the pins during handling. For storage, the specified range of -35°C to +85°C in a dry, anti-static environment is recommended to prevent moisture absorption (which can cause \"popcorning\" during reflow) and electrostatic discharge damage.

7. Packaging & Ordering Information

The part number is LTP-2157AKY. While specific packaging details (reel, tray, tube) are not listed in the provided content, such displays are typically supplied in anti-static tubes or trays to protect the pins and the display face. The \"Spec No.: DS-30-99-106\" and \"BNS-OD-FC001/A4\" are internal document control numbers.

8. Application Recommendations

8.1 Typical Application Circuits

The LTP-2157AKY requires an external driver circuit. A common design uses a microcontroller with multiplexing software. The microcontroller's I/O ports, often insufficient to source/sink the required current directly, are connected to row driver transistors (e.g., PNP or P-channel MOSFETs for sourcing current to anodes) and column driver transistors or dedicated sink drivers (e.g., NPN, N-channel MOSFETs, or LED driver ICs like the ULN2003 for sinking current from cathodes). The multiplexing routine rapidly cycles through each row (1-7), turning on the appropriate column cathodes for that row to form the desired character. The 1/16 duty cycle mentioned in the test condition is a typical multiplexing ratio (e.g., 1 row on at a time out of a possible 7+? frames; the exact timing depends on the driver design).

8.2 Design Considerations

• Current Limiting: Essential for every LED segment. Use resistors or constant current drivers. Calculate the resistor value based on the supply voltage (V_CC), the LED forward voltage (V_F), and the desired forward current (I_F). For multiplexed operation, use the peak current (I_p). Example: For V_CC=5V, V_F=2.6V, I_p=32mA, R = (5V - 2.6V) / 0.032A ≈ 75 Ohms.
• Multiplexing Frequency: Must be high enough to avoid visible flicker (typically >60 Hz frame rate). The persistence of vision will blend the rapidly cycling rows into a stable image.
• Heat Dissipation: Adhere to the current derating curve at high ambient temperatures. Ensure adequate ventilation if used in enclosed spaces.
• Viewing Angle: While not specified, standard LED matrices have a wide viewing angle. The gray face/white dot design optimizes contrast for frontal viewing.

9. Technical Comparison

Compared to other contemporary display technologies available at its release time (2002), the LTP-2157AKY offered distinct advantages:

• vs. Incandescent or Vacuum Fluorescent Displays (VFDs): The LED display is far more power-efficient, generates less heat, offers faster response time, and has a significantly longer lifetime. It is also more mechanically robust as it has no fragile filaments or glass envelopes.
• vs. Early LCDs: The LED display is self-illuminating, providing much higher brightness and better visibility in low-light or direct sunlight conditions without a backlight. It also has a wider operating temperature range and no slow response issues in cold environments.
• vs. Other LED Colors (e.g., GaAsP Red): The AlInGaP technology used in this amber yellow LED provides higher luminous efficiency (more light output per unit of electrical power) and better long-term stability than older GaAsP red LEDs.

10. Frequently Asked Questions (FAQs)

Q1: Can I drive this display with a constant 5V supply on the anodes?
A1: No. LEDs are current-driven devices. Applying a constant voltage without a series current-limiting resistor will cause excessive current to flow, potentially destroying the LED. Always use a current-limiting mechanism.

Q2: Why are there two pins for Column 3 and Row 4?
A2: Pins 4 & 11 are both connected to Cathode Column 3 internally, and Pins 5 & 12 are both connected to Anode Row 4. This is likely done for internal wire bonding layout efficiency or to provide alternative connection points on the PCB for routing convenience. Electrically, they are the same node.

Q3: What does \"1/16 Duty\" mean in the luminous intensity test condition?
A3: It means the LED was pulsed with a duty cycle of 1/16 (6.25%). The peak current (I_p=32mA) is higher than the average DC current would be for the same brightness perception in a multiplexed system. The average current is I_p * duty cycle = 32mA * 0.0625 = 2mA. This pulsed operation is standard for testing multiplexed displays.

Q4: How do I display a character like the letter \"A\"?
A4: You need a font map or lookup table that defines which dots (row, column intersections) to illuminate for each character. For a 5x7 matrix, this is typically a 5-byte array per character, where each bit in a byte represents a row element in one column. Your microcontroller software uses this map during the multiplexing scan.

11. Practical Design Case Study

Consider designing a simple digital thermometer with a 3-digit readout using three LTP-2157AKY displays. The system would require a temperature sensor, a microcontroller (e.g., an 8-bit MCU), and driver circuitry. The microcontroller reads the sensor, converts the value to BCD or a custom font map, and drives the displays. Due to the number of pins (3 displays * 14 pins = 42 pins if driven directly), a multiplexing scheme is mandatory. The design would involve: 1) Connecting all corresponding row pins (anodes) of the three displays together (creating 7 common anode lines). 2) Connecting the column pins (cathodes) of each display separately (creating 3 displays * 5 columns = 15 cathode lines). 3) Using the microcontroller with 7+15=22 I/O lines (or fewer with external shift registers or port expanders) to scan the common rows and activate the appropriate columns for each digit sequentially at a high frequency. Current-limiting resistors would be placed on either the common anode lines or the individual cathode lines.

12. Operating Principle

The LTP-2157AKY is based on the electroluminescence principle of a semiconductor P-N junction. When forward-biased, electrons from the N-type AlInGaP layer recombine with holes from the P-type layer in the active region. This recombination event releases energy in the form of photons (light). The specific wavelength of 595 nm (amber yellow) is determined by the bandgap energy of the AlInGaP semiconductor material, which is engineered during the crystal growth process. The non-transparent GaAs substrate helps reflect light upward, improving overall light extraction efficiency from the top surface of the chip.

13. Technology Trends

Since the release of this datasheet (2002), LED display technology has advanced significantly. While the 5x7 dot matrix format remains a workhorse for simple displays, the underlying technology has evolved. AlInGaP LEDs have seen improvements in efficiency and lifetime. Furthermore, newer display options have become prevalent: 1) Higher Density Matrices: 8x8, 16x16, and larger graphic matrices are now common and inexpensive. 2) Surface-Mount Device (SMD) LEDs: Modern designs often use individual SMD LEDs placed on a PCB to form a matrix, offering more design flexibility. 3) Organic LED (OLED) Displays: Provide high contrast, wide viewing angles, and flexible form factors, though they may have different lifetime and environmental constraints. 4) Integrated Controller Displays: Modern modules often include a built-in controller (like HD44780 for character LCDs or dedicated LED matrix drivers) that simplifies interface requirements to just a few data and control lines. The fundamental design principles for driving a multiplexed LED array, however, as detailed for the LTP-2157AKY, remain directly applicable to many modern discrete LED matrix projects.