LTC-47C1SW LED Display Datasheet - 0.4-inch Digit Height - White Color - 3.2V Forward Voltage - 35mW Power Dissipation - English Technical Document

1. Product Overview

The LTC-47C1SW is a quadruple-digit, seven-segment alphanumeric display module. It features a digit height of 0.4 inches (10.16 mm), making it suitable for applications requiring clear, medium-sized numeric readouts. The display utilizes white light-emitting diodes (LEDs) based on InGaN (Indium Gallium Nitride) semiconductor technology mounted on a sapphire substrate. The device presents a high-contrast appearance with white luminous segments against a black background face. It is constructed as a lead-free package in compliance with RoHS (Restriction of Hazardous Substances) directives.

1.1 Core Advantages and Target Market

This display offers several key benefits for electronic design engineers. Its low power requirement makes it energy-efficient, while the high brightness and excellent character appearance ensure readability in various lighting conditions. The wide viewing angle is crucial for applications where the display may be viewed from off-axis positions. The solid-state reliability inherent to LED technology provides long operational life and resistance to shock and vibration. These characteristics make the LTC-47C1SW ideal for consumer electronics, industrial instrumentation, test and measurement equipment, point-of-sale terminals, and automotive dashboard displays where reliable, clear numeric information is required.

2. Technical Parameters Deep Objective Interpretation

2.1 Photometric and Electrical Characteristics

The performance of the LTC-47C1SW is defined under standard test conditions at an ambient temperature (Ta) of 25°C. The key parameters provide a comprehensive understanding of its operational envelope.

• Luminous Intensity (Iv): The typical luminous intensity per segment is 18 millicandelas (mcd) when driven with a forward current (IF) of 10 mA. The minimum specified value is 12.8 mcd. This parameter quantifies the perceived brightness of the lit segment.
• Forward Voltage (VF): The voltage drop across an LED segment when conducting current. For this device, the typical forward voltage is between 2.70V and 3.2V at a test current of 5 mA. This value is critical for designing the current-limiting circuitry in the driver.
• Chromaticity Coordinates (x, y): These coordinates define the color point of the white light on the CIE 1931 chromaticity diagram. The typical values provided (x=0.294, y=0.286) indicate a specific shade of white. A tolerance of ±0.01 is applied to these coordinates.
• Reverse Current (IR): The maximum leakage current when a reverse bias of 5V is applied is 100 µA. It is important to note that this parameter is for test purposes only; the device is not intended for continuous operation under reverse voltage.
• Crosstalk: A specification of ≤ 2.5% indicates the maximum allowable light leakage or electrical interference between adjacent segments or digits, ensuring character clarity.

2.2 Absolute Maximum Ratings

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

• Power Dissipation per Segment: 35 mW maximum.
• Peak Forward Current per Segment: 50 mA maximum, under pulsed conditions (1 kHz frequency, 10% duty cycle).
• Continuous Forward Current per Segment: The maximum continuous current is derated linearly from its value at 25°C at a rate of 0.125 mA/°C as the ambient temperature increases.
• Operating Temperature Range: -35°C to +80°C.
• Storage Temperature Range: -35°C to +105°C.
• Soldering Conditions: The device can withstand wave or reflow soldering with the temperature at a point 1/16 inch (approximately 1.6 mm) below the seating plane not exceeding 260°C for 3 seconds.

3. Binning System Explanation

The LTC-47C1SW employs a hue binning system to categorize devices based on their precise white color point. This is essential for applications requiring color consistency across multiple displays or within a multi-digit unit. The bins are defined by quadrilaterals on the CIE 1931 chromaticity diagram, specified by their corner coordinates (x, y). The datasheet lists several bins (e.g., S1-2, S2-2, S3-1, S3-2, S4-1, S4-2, S5-1, S6-1). Each bin has a defined tolerance of ±0.01 on both the x and y coordinates. This system allows manufacturers to select LEDs from specific bins to achieve a uniform white appearance across all segments and digits, minimizing visual color variation.

4. Mechanical and Packaging Information

4.1 Dimensions and Tolerances

The package outline drawing provides critical mechanical dimensions for PCB (Printed Circuit Board) layout and assembly. All primary dimensions are in millimeters with a standard tolerance of ±0.25 mm unless otherwise specified.

• Pin Tip Shift Tolerance: The allowable deviation in the position of the pin tips is ±0.25 mm.
• Spacer Detail: A spacer feature is designed to allow a slip-out tolerance of ±0.5 mm, likely aiding in alignment during assembly.
• Recommended PCB Hole Diameter: 0.9 mm is suggested for the leads.

4.2 Visual and Cosmetic Specifications

The datasheet includes several quality control parameters related to the display's appearance:

• Foreign material on a segment must be ≤ 10 mils (0.254 mm).
• Ink contamination on the surface must be ≤ 20 mils (0.508 mm).
• Bending of the reflector must be ≤ 1% of its length.
• Bubbles within a segment must be ≤ 10 mils (0.254 mm).
• A specific note mandates the use of \"hardness pin only,\" indicating a requirement for pins with sufficient mechanical rigidity.

5. Internal Circuit and Pin Configuration

The LTC-47C1SW is a common cathode display. The internal circuit diagram shows that each of the four digits shares its cathode connection. The seven segments (A, B, C, D, E, F, G) and two decimal points (DP1, DP2) have their anodes connected in a multiplexed arrangement. Specifically, the anodes for segments are grouped between digit pairs (Digits 1 & 2 and Digits 3 & 4) to facilitate time-division multiplexing, a common technique to control multi-digit displays with fewer driver pins.

The 20-pin connection table is essential for correct wiring:

• Pins 5, 10, 15, 20 are the common cathodes for digits 2, 4, 3, and 1 respectively.
• Pins 2 and 7 are the anodes for decimal points DP1 and DP2.
• The remaining pins are the anodes for the various segments (A-G), shared between specific digit pairs as indicated in the table. For example, Pin 1 is the anode for segment D for digits 1 and 2.

6. Soldering and Assembly Guidelines

Proper handling and assembly are crucial for reliability. The device is sensitive to Electrostatic Discharge (ESD). It is strongly recommended to use a wrist strap or anti-static gloves during handling, and to ensure all equipment and workstations are properly grounded.

For soldering, the key parameter is to limit the temperature at the device body. The specification allows for a maximum temperature of 260°C measured 1.6 mm below the seating plane for a duration of 3 seconds during wave or reflow soldering processes. Adhering to these limits prevents thermal damage to the LED chips and the plastic package.

7. Application Suggestions

7.1 Typical Application Circuits

The common cathode, multiplexed anode structure is designed for use with a microcontroller or dedicated LED driver IC. A typical circuit involves using transistor switches (e.g., NPN BJTs or N-channel MOSFETs) to sink current through the cathode of each digit sequentially (digit scanning). The segment anode lines are driven with the appropriate pattern via current-limiting resistors. The multiplexing frequency should be high enough (typically >60 Hz) to avoid visible flicker due to persistence of vision.

7.2 Design Considerations

• Current Limiting: External resistors are mandatory for each anode line to set the forward current (e.g., 5-10 mA per segment as per datasheet). The resistor value can be calculated using R = (Vcc - VF) / IF, where Vcc is the supply voltage, VF is the forward voltage of the LED (use max value for safety), and IF is the desired forward current.
• Driver Capability: The driver IC or microcontroller port must be able to source the cumulative current for all lit segments in one digit during its active time.
• Viewing Angle: The wide viewing angle allows flexibility in mounting position relative to the user.
• Thermal Management: While power dissipation is low, ensuring adequate ventilation in the enclosure helps maintain LED longevity, especially at higher ambient temperatures.

8. Technical Comparison and Differentiation

Compared to other seven-segment displays, the LTC-47C1SW's use of InGaN white SMD chips offers advantages over older technologies like red GaAsP LEDs or filtered white LEDs. InGaN LEDs generally provide higher efficiency, better color stability over time, and a more consistent white color point. The 0.4-inch digit height positions it between smaller displays used in portable devices and larger ones for signage. Its multiplexed pinout is a standard design that minimizes the required number of controller I/O pins for a 4-digit display, offering a cost-effective and space-efficient solution compared to displays with individually driven pins for each segment of each digit.

9. Frequently Asked Questions Based on Technical Parameters

Q: What is the purpose of the hue binning system?
A: The hue binning ensures color consistency. For a multi-digit display, using LEDs from the same or adjacent bins guarantees that all digits emit an identical shade of white, preventing one digit from looking noticeably different (e.g., bluer or yellower) than its neighbors.

Q: Can I drive this display with a 5V microcontroller?
A: Yes, but you must use current-limiting resistors. Since the typical forward voltage is around 3V, a 5V supply would force excessive current through the LED without a resistor, potentially destroying it. A series resistor is always required.

Q: What does \"common cathode\" mean for my circuit design?
A: Common cathode means all the LEDs in one digit share a negative (ground) connection. To light a digit, you connect its cathode pin to ground (via a transistor switch) and apply a positive voltage (through a current-limiting resistor) to the anodes of the segments you wish to illuminate.

Q: How do I interpret the peak forward current rating?
A: The 50 mA peak rating at 10% duty cycle allows for brief pulses of higher current to achieve greater instantaneous brightness in a multiplexed system. The average current over time must not exceed the continuous current rating, which is lower and derated with temperature.

10. Operating Principle Introduction

A seven-segment display is an assembly of light-emitting diodes arranged in a figure-eight pattern. By selectively illuminating specific segments (labeled A through G), it can form all ten numerals (0-9) and some letters. The LTC-47C1SW integrates four such digit arrays into a single package. The InGaN semiconductor material used in the LEDs emits blue light when electrons recombine with holes across the material's bandgap. This blue light is partially converted to longer wavelengths (yellow) by a phosphor coating inside the LED package, resulting in the perception of white light by the human eye. The multiplexing technique used to control four digits with one set of segment drivers works by rapidly cycling power to each digit in sequence. Only one digit is lit at any instant, but due to the persistence of human vision, all four digits appear to be continuously illuminated if the cycling frequency is sufficiently high.

11. Development Trends

The trend in seven-segment display technology continues to focus on several key areas. Efficiency improvements in InGaN LED chips lead to higher brightness at lower drive currents, reducing power consumption and heat generation. There is also a move towards even higher color consistency and a wider range of available white color temperatures (e.g., cool white, neutral white, warm white) to better match application aesthetics. Integration is another trend, with some displays incorporating the driver IC and current-limiting resistors within the same module, simplifying the design for the end engineer. Furthermore, advancements in packaging may allow for thinner profiles and increased ruggedness for harsh environment applications.