LTC-4798SW 0.39-inch Quadruple Digit White LED Display Datasheet - Digit Height 9.9mm - Forward Voltage 2.7-3.2V - Power 35mW per Segment - English Technical Documentation

1. Product Overview

The LTC-4798SW is a quadruple-digit, seven-segment alphanumeric display module. Its primary function is to present numerical and limited alphanumeric information in electronic devices. The core technology is based on InGaN (Indium Gallium Nitride) white LED chips mounted on a transparent substrate. This device features a white face and white segments, providing a clean and high-contrast visual appearance. It is categorized as a multiplex common cathode display, meaning the cathodes of the LEDs for each digit are connected together, allowing for efficient control of multiple digits with a reduced number of driver pins.

1.1 Core Advantages and Target Market

The display offers several key advantages that make it suitable for a variety of applications. Its high brightness and high contrast ensure excellent readability even in well-lit environments. The wide viewing angle of 130 degrees allows the display to be viewed clearly from various positions. It has a low power requirement, contributing to energy efficiency in the end product. The solid-state reliability of LED technology ensures long operational life and resistance to shock and vibration. The device uses a lead-free package, complying with RoHS (Restriction of Hazardous Substances) directives, making it suitable for global markets with strict environmental regulations. The primary target markets include industrial instrumentation, consumer appliances, point-of-sale terminals, medical devices, and automotive dashboard displays where clear, reliable numeric readouts are required.

2. In-Depth Technical Parameter Analysis

This section provides a detailed, objective interpretation of the electrical, optical, and thermal characteristics specified in the datasheet.

2.1 Photometric and Optical Characteristics

The average luminous intensity (Iv) is specified between 71 and 146 millicandelas (mcd) at a standard test current of 5mA. This parameter defines the brightness of each illuminated segment. The datasheet notes that the luminous intensity is categorized, meaning devices are binned and marked according to their measured output, allowing designers to select displays with consistent brightness levels. The viewing angle (2θ1/2) is 130 degrees, which is the full angle at which the luminous intensity drops to half of its maximum value measured on-axis. This wide angle is a significant advantage for applications where the user may not be directly in front of the display. The chromaticity coordinates (x, y) are provided as typical values (x=0.304, y=0.3) under the 1931 CIE chromaticity diagram, defining the white point of the emitted light. A tolerance of ±0.01 is applied to these coordinates in the binning system.

2.2 Electrical Parameters

The forward voltage (Vf) per segment ranges from 2.7V to 3.2V at a forward current (If) of 5mA. This is a critical parameter for designing the current-limiting circuitry for the LEDs. The absolute maximum ratings define the operational limits: the continuous forward current per segment must not exceed 10mA, and the peak forward current (under pulsed conditions of 1kHz, 10% duty cycle) must not exceed 50mA. The power dissipation per segment is limited to 35mW. Exceeding these ratings can lead to permanent degradation or failure. The reverse current (Ir) is specified as a maximum of 100µA at a reverse voltage (Vr) of 5V. The datasheet explicitly cautions that this reverse voltage condition is for test purposes only and the device should not be continuously operated under reverse bias, as LEDs are not designed to withstand significant reverse voltage.

2.3 Thermal Characteristics

The operating and storage temperature range for the device is from -35°C to +85°C. This wide range makes it suitable for use in environments subject to significant temperature variations. A forward current derating factor is specified: for every degree Celsius above 25°C, the maximum allowable continuous forward current must be reduced by 0.28mA. This is a crucial design consideration to prevent thermal runaway and ensure long-term reliability, especially in high ambient temperature applications. The soldering condition is specified as 260°C for 3 seconds at a distance of 1/16 inch (approximately 1.6mm) below the seating plane, which is a standard lead-free reflow profile.

3. Binning System Explanation

The product utilizes a comprehensive binning system to ensure consistency in key parameters. This allows manufacturers to select components that match their specific requirements for uniformity in multi-display setups.

3.1 Forward Voltage (Vf) Binning

Devices are sorted into bins based on their forward voltage at 5mA. The bins are labeled 3 through 7, with Vf ranges from 2.7-2.8V (Bin 3) up to 3.1-3.2V (Bin 7). A tolerance of ±0.1V is applied to each bin. Selecting displays from the same Vf bin helps ensure uniform brightness when driven by a constant voltage source with series resistors, as the current through each segment will be more consistent.

3.2 Luminous Intensity (Iv) Binning

This is a critical binning parameter for visual uniformity. The bins are labeled with alphanumeric codes (Q11, Q12, Q21, Q22, R11, R12). The luminous intensity ranges from a minimum of 71.0 mcd (Q11 min) to a maximum of 146.0 mcd (R12 max). A tolerance of ±15% is applied to each bin. The Iv classification code is marked on each packing bag, facilitating traceability and selection.

3.3 Hue (Chromaticity) Binning

The white color point is controlled through hue binning. The datasheet defines several bins (S3-1, S3-2, S4-1, S4-2) with specific boundaries on the CIE 1931 chromaticity coordinates (x, y). These boundaries form quadrilaterals on the color chart. A tolerance of ±0.01 is applied to the (x, y) coordinates within each bin. This binning ensures that all segments and digits within a display, and across multiple displays, emit light of a consistent white color, avoiding noticeable color shifts.

4. Performance Curve Analysis

While the provided PDF excerpt mentions typical characteristic curves, the specific graphs are not included in the text. Based on standard LED behavior, these curves would typically illustrate the relationship between forward current and luminous intensity (showing a near-linear increase within the operating range), the relationship between forward voltage and forward current (the diode I-V curve), and the variation of luminous intensity with ambient temperature (showing a decrease as temperature increases). Understanding these relationships is essential for designing robust driver circuits that maintain consistent brightness over the intended operating conditions.

5. Mechanical and Package Information

5.1 Dimensions and Tolerances

The device has a digit height of 0.39 inches (9.9 mm). All package dimensions are provided in millimeters. General tolerances are ±0.25 mm unless otherwise specified. Key mechanical notes include: pin tip shift tolerance is ±0.4 mm; foreign material on a segment must be ≤10 mils; surface ink contamination must be ≤20 mils; bending must be ≤1% of the reflector length; and bubbles within a segment must be ≤10 mils. The recommended PCB hole diameter for the pins is 1.0 mm.

5.2 Pinout and Polarity Identification

The display has 12 pins. The internal circuit diagram and pin connection table show it is a multiplex common cathode type. The anodes for the individual segments (A through G, and DP) and the common cathodes for the four digits are assigned to specific pin numbers. For example, Pin 12 is the common cathode for Digit 1, Pin 9 for Digit 2, Pin 8 for Digit 3, and Pin 6 for Digit 4. Correct identification of the common cathode pins is essential for the multiplexing drive scheme.

6. Soldering and Assembly Guidelines

The absolute maximum rating section specifies the soldering condition: 260°C for 3 seconds at 1/16 inch (1.6mm) below the seating plane. This corresponds to a standard lead-free reflow profile. It is critical to adhere to this to prevent thermal damage to the LED chips or the plastic package. The datasheet includes a strong caution regarding Electrostatic Discharge (ESD). LEDs are sensitive to ESD, and proper handling procedures must be followed: using wrist straps or anti-static gloves, and ensuring all equipment and workstations are properly grounded. For storage, the specified temperature range is -35°C to +85°C, and devices should be kept in their original moisture-barrier bags until use.

7. Application Recommendations

7.1 Typical Application Scenarios

This display is ideal for applications requiring a clear, multi-digit numeric readout. Common uses include digital multimeters, frequency counters, clock and timer displays, industrial process control readouts, medical monitoring equipment (e.g., blood pressure monitors), household appliances (ovens, microwaves), and instrumentation panels.

7.2 Design Considerations

Driver Circuit: A multiplexing driver circuit is required. This involves sequentially enabling each digit's common cathode while supplying the appropriate segment anode data for that digit. The switching must be fast enough to avoid visible flicker (typically >60Hz refresh rate).
Current Limiting: External current-limiting resistors are mandatory for each segment anode (or a constant current driver IC can be used). The resistor value is calculated based on the supply voltage, the LED forward voltage (use max Vf for a safe design), and the desired forward current (must not exceed 10mA continuous).
Thermal Management: In high ambient temperature applications, the forward current derating (0.28mA/°C above 25°C) must be applied. This may require reducing the operating current to stay within the safe power dissipation limit.
Optical Integration: Consider the wide 130-degree viewing angle when designing the product enclosure and window. Filters or diffusers may be used to enhance contrast in bright ambient light.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the binning codes on the packing bag?
A: The binning codes (for Vf, Iv, and Hue) allow you to select displays with closely matched electrical and optical characteristics. This is crucial for achieving uniform brightness and color across all digits in your application, especially if using multiple displays side-by-side.
Q: Can I drive this display with a 5V supply?
A: Yes, but you must use a current-limiting resistor in series with each segment. For example, with a 5V supply and assuming a maximum Vf of 3.2V and a desired If of 5mA, the resistor value would be R = (5V - 3.2V) / 0.005A = 360 Ohms. A standard 360Ω or 390Ω resistor would be suitable.
Q: Why is there a peak forward current rating (50mA) much higher than the continuous rating (10mA)?
A: The peak rating allows for pulsed operation, which is the basis of multiplexing. In a multiplexed setup, each digit is only powered for a fraction of the time (duty cycle). To achieve the same apparent brightness as a continuously driven segment, the pulsed current can be higher, as long as the average power dissipation remains within limits.
Q: What happens if I exceed the storage temperature range?
A: Exceeding the limits, especially on the high side, can accelerate aging of the LED chips and the plastic package, potentially leading to premature darkening of the epoxy (lumen depreciation) or mechanical failure. On the low side, thermal stress could cause cracking.

9. Operational Principle

The LTC-4798SW operates on the principle of electroluminescence in semiconductor materials. The InGaN LED chip emits blue light when a forward current is applied across its p-n junction. This device uses a phosphor coating (not explicitly stated but implied by "white LED") which absorbs a portion of the blue light and re-emits it as yellow light. The combination of the remaining blue light and the converted yellow light is perceived by the human eye as white. The seven-segment format is a standardized arrangement of seven rectangular LEDs (segments) that can be individually controlled to form numeric digits (0-9) and some letters. The multiplex common cathode architecture is a wiring technique that reduces the number of required control pins from (7 segments + 1 decimal point) * 4 digits = 32 pins down to 7 segment anodes + 4 digit cathodes + 1 common DP anode = 12 pins. This is achieved by rapidly cycling power to each digit in sequence while illuminating the correct segments for that digit.