LTC-3620KG 7-Segment LED Display Datasheet - 0.39-inch Digit Height - AlInGaP Green - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-3620KG is a high-performance, 0.39-inch (10 mm) digit height, 7-segment LED display module. It is designed for applications requiring clear, bright numeric readouts with excellent visibility. The device utilizes advanced AlInGaP (Aluminum Indium Gallium Phosphide) LED chip technology, which is known for its high efficiency and superior luminous intensity compared to traditional materials. The segments are presented in a gray and white color scheme, enhancing contrast and readability. This display is categorized for luminous intensity and is offered in a lead-free package compliant with RoHS directives, making it suitable for modern electronic designs with environmental considerations.

2. Technical Specifications Deep Dive

2.1 Optical Characteristics

The optical performance is a key strength of this display. At a standard test current of 1mA, the average luminous intensity (Iv) ranges from a minimum of 200 µcd to a typical value of 585 µcd. At a higher drive current of 10mA, the typical intensity increases significantly to 6435 µcd, demonstrating the high-brightness capability of the AlInGaP chips. The device emits green light with a peak emission wavelength (λp) of 571 nm and a dominant wavelength (λd) of 572 nm, both measured at IF=20mA. The spectral line half-width (Δλ) is 15 nm, indicating a relatively pure color emission. Luminous intensity is measured using a sensor and filter combination that approximates the CIE photopic eye-response curve for accuracy.

2.2 Electrical Characteristics

Electrically, the display is designed for low-power operation. The forward voltage (VF) per segment is typically 2.6V with a maximum of 2.6V when driven at 20mA. The reverse current (IR) per segment is specified at a maximum of 100 µA at VR=5V, though it is noted that continuous operation under reverse bias is not intended. The luminous intensity matching ratio between segments is 2:1 maximum at IF=1mA, ensuring uniform appearance across the display. A cross-talk specification of ≤ 2.5% is defined to minimize unwanted illumination between adjacent segments.

2.3 Absolute Maximum Ratings

The device is rated for robust operation within specified limits. The maximum power dissipation per chip is 70 mW. The peak forward current per chip is 60 mA, but only under pulsed conditions (1/10 duty cycle, 0.1ms pulse width). The continuous forward current per chip is 25 mA at 25°C, derating linearly at 0.28 mA/°C as temperature increases. The operating and storage temperature range is from -35°C to +105°C. For assembly, the maximum solder temperature is 260°C for a maximum of 3 seconds at a distance of 1.6mm below the seating plane.

3. Mechanical and Package Information

3.1 Package Dimensions

The display has a specific physical footprint. All dimensions are provided in millimeters with standard tolerances of ±0.25mm unless otherwise noted. Key dimensional notes include a pin tip shift tolerance of ±0.4mm, a limit on foreign material on segments (≤10 mils), and a limit on surface ink contamination (≤20 mils). Bending of the reflector must not exceed 1% of its length. The recommended PCB hole diameter for the pins is 1.0 mm. A spacer detail allows for a slip-out tolerance of ±0.5 mm.

3.2 Pin Configuration and Internal Circuit

The LTC-3620KG is a common anode configuration device. The pin connection table is as follows: Pin 2 is the common anode for Digit 1, Pin 6 for Digit 2, and Pin 8 for Digit 3. The segment cathodes are assigned to specific pins: A (Pin 13), B (Pin 12), C (Pin 4), D (Pin 5), E (Pin 3), F (Pin 16), and G (Pin 9). Pin 7 is the cathode for the decimal points (L / L1 / L2). Pins 1, 10, 11, 14, and 15 are noted as having no connection (NO PIN). The internal circuit diagram shows the common anode connections for the three digits, with each digit's segments connected in parallel to their respective cathode pins.

4. Performance Curve Analysis

The datasheet includes a section for typical electrical and optical characteristic curves, measured at an ambient temperature of 25°C unless otherwise noted. These curves are essential for designers to understand the device's behavior under different operating conditions. While the specific graphs are not detailed in the provided text, typical curves for such a product would include the relationship between forward current (IF) and forward voltage (VF), the relationship between forward current (IF) and luminous intensity (Iv), and the variation of luminous intensity with ambient temperature. Analyzing these curves allows for optimal drive current selection to achieve desired brightness while maintaining efficiency and longevity.

5. Soldering and Assembly Guidelines

Proper handling is crucial for reliability. The maximum soldering temperature is explicitly defined as 260°C for a maximum duration of 3 seconds, measured 1.6mm below the seating plane of the component. This is a critical parameter for wave soldering or reflow processes to prevent thermal damage to the LED chips or the plastic package. Designers should ensure their PCB assembly profiles adhere to this limit. Furthermore, the notes on dimensional tolerances, such as pin shift and spacer slip, should be considered during PCB layout and mechanical design to ensure proper fit and alignment.

6. Application Suggestions

6.1 Typical Application Scenarios

This display is ideal for applications requiring clear, medium-sized numeric readouts. Common uses include industrial instrument panels, test and measurement equipment, medical devices, consumer appliances (like microwaves or ovens), point-of-sale terminals, and automotive aftermarket displays. Its high brightness and wide viewing angle make it suitable for environments with high ambient light or where the display needs to be read from various angles.

6.2 Design Considerations

When designing with the LTC-3620KG, several factors must be considered. First, the common anode configuration requires a current-sinking driver circuit (e.g., a transistor or dedicated LED driver IC) to control the cathodes. Current-limiting resistors are mandatory for each segment cathode to set the desired forward current and brightness, calculated based on the supply voltage and the LED's forward voltage. The high luminous intensity at low currents (e.g., 1mA) allows for very low-power designs. Designers should also account for the power dissipation limits and implement proper derating if the operating ambient temperature is expected to be high. The wide operating temperature range (-35°C to +105°C) makes it robust for harsh environments.

7. Technical Comparison and Differentiation

The primary differentiating factor of the LTC-3620KG is its use of AlInGaP semiconductor material for the green LED chips. Compared to older technologies like standard GaP (Gallium Phosphide) green LEDs, AlInGaP offers significantly higher luminous efficiency and brightness for the same drive current. This results in better visibility and lower power consumption. The "categorized for luminous intensity" feature indicates that devices are binned or sorted based on their light output, allowing for more consistent brightness across production runs and in multi-digit displays. The lead-free, RoHS-compliant construction aligns with global environmental regulations.

8. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the "NO PIN" connections?
A: The "NO PIN" designations (Pins 1, 10, 11, 14, 15) are likely for mechanical symmetry and stability during the molding process. They are not electrically connected to any internal component and should be left unconnected (floating) in the circuit.

Q: How do I control the decimal points?
A: The decimal points (L, L1, L2) share a common cathode on Pin 7. To illuminate a specific decimal point, you would activate (pull low) Pin 7 while also enabling the common anode of the digit where that decimal point is located (Pin 2, 6, or 8). The internal diagram would clarify the exact mapping.

Q: Can I drive this display with a microcontroller directly?
A: It is possible but requires careful design. A microcontroller's GPIO pins can typically sink or source only a limited current (often 20-25mA). Since the display's continuous current per segment is 25mA max, driving multiple segments simultaneously could exceed the microcontroller's total current rating. It is highly recommended to use external driver transistors or a dedicated LED driver IC to handle the current and multiplexing, protecting the microcontroller.

Q: What does "luminous intensity matching ratio 2:1" mean?
A: This specification means that the luminous intensity of the brightest segment will not be more than twice the intensity of the dimmest segment within the same device, when measured under identical conditions (IF=1mA). This ensures a reasonably uniform appearance, avoiding one segment looking much brighter than another.

9. Design and Usage Case Example

Consider designing a simple 3-digit voltmeter display. The microcontroller would measure a voltage, convert it to a 3-digit number, and need to display it. The LTC-3620KG's three common anodes (Pins 2, 6, 8) would be connected to the collector of three PNP transistors (or similar), whose bases are controlled by microcontroller pins. The seven segment cathodes (Pins 3, 4, 5, 9, 12, 13, 16) and the decimal point cathode (Pin 7) would each connect to a current-limiting resistor and then to the drain of an N-channel MOSFET (or similar), whose gate is controlled by the microcontroller. The firmware would implement multiplexing: turn on the transistor for Digit 1, set the MOSFETs for the segments needed to display the first digit, wait a short time, then turn off Digit 1 and repeat for Digits 2 and 3 in rapid succession. This multiplexing reduces the number of required driver pins and allows constant, flicker-free illumination.

10. Operating Principle Introduction

A 7-segment LED display is a collection of light-emitting diodes arranged in a figure-eight pattern. Each of the seven segments (labeled A through G) is an individual LED. An additional LED is often used for a decimal point. In a common anode configuration like the LTC-3620KG, the anodes of all LEDs for a given digit are connected together to a common positive voltage supply pin. The cathode of each individual segment LED is brought out to a separate pin. To illuminate a specific segment, its common anode pin must be driven to a voltage higher than the cathode voltage (applying forward bias), and the corresponding cathode pin must be connected to a lower voltage (typically ground through a current-limiting resistor). By controlling which cathode pins are grounded while a particular common anode is active, specific numeric or alphanumeric characters can be formed.

11. Technology Trends

While discrete 7-segment LED displays remain relevant for specific applications, the broader trend in display technology is towards integration and flexibility. Integrated driver chips with built-in controllers (for clock, temperature, etc.) are becoming more common, simplifying the design. There is also a shift towards surface-mount device (SMD) packages for automated assembly, though through-hole types like this one are still valued for prototyping, repair, and high-vibration environments. In terms of materials, AlInGaP represents an advanced step for red, orange, amber, and green LEDs, but for full-color capabilities, InGaN (Indium Gallium Nitride) is the dominant technology for blue and green, and is often used with phosphors to create white light. The future may see more hybrid or customizable multi-digit modules that combine display, driver, and interface logic into a single compact unit.