LTC-4665JD LED Display Datasheet - 0.39-inch Digit Height - AlInGaP Red - Low Power - English Technical Document

1. Product Overview

The LTC-4665JD is a compact, triple-digit, seven-segment alphanumeric display module. Its primary function is to provide clear, bright numeric and limited alphanumeric readouts in electronic equipment. The core application areas include instrumentation panels, test and measurement equipment, industrial control systems, and consumer electronics where low-power, reliable numeric indication is required.

The device's key positioning lies in its balance of performance and efficiency. It is engineered for applications where power consumption is a critical design constraint, without compromising on readability. The display offers excellent character appearance due to its continuous uniform segments, ensuring a cohesive and professional look. Its high brightness and contrast ratio make it suitable for use in various ambient lighting conditions, from dimly lit environments to areas with significant ambient light.

The target market encompasses both industrial and commercial electronic manufacturers. Design engineers seeking a reliable, low-maintenance display solution for control panels, counters, timers, or status indicators will find this component suitable. Its solid-state reliability, stemming from the LED technology, makes it preferable over older technologies like vacuum fluorescent or incandescent displays in terms of longevity and shock resistance.

2. Technical Parameter Deep Dive

2.1 Photometric & Optical Characteristics

The optical performance is central to the display's functionality. The device utilizes Aluminium Indium Gallium Phosphide (AlInGaP) high-efficiency red LED chips. This semiconductor material is known for its high luminous efficacy in the red/orange/amber spectrum. The chips are fabricated on a non-transparent Gallium Arsenide (GaAs) substrate, which helps in directing light output forward and improves contrast by reducing internal reflections and light leakage.

Luminous Intensity (I_V): The average luminous intensity per segment is specified with a minimum of 200 \u00b5cd and a maximum of 650 \u00b5cd at a forward current (I_F) of 1 mA. This low-current operation point is a defining feature, highlighting its efficiency. The typical value would be towards the middle of this range, providing sufficient brightness for most indoor applications while consuming minimal power.

Wavelength Characteristics: The peak emission wavelength (\u03bb_p) is typically 656 nm, placing it in the bright red portion of the visible spectrum. The dominant wavelength (\u03bb_d) is 640 nm. The difference between peak and dominant wavelength is influenced by the spectral shape. The spectral line half-width (\u0394\u03bb) is 22 nm, indicating a relatively pure color emission with minimal spread into adjacent colors, which contributes to a saturated red appearance.

Luminous Intensity Matching Ratio (I_V-m): This parameter, with a maximum ratio of 2:1, ensures uniformity across the display. It means the brightness of the dimmest segment will be no less than half the brightness of the brightest segment under the same driving conditions (I_F=10mA). This is crucial for achieving a consistent and professional visual output where no one segment appears noticeably darker than another.

2.2 Electrical Characteristics

The electrical parameters define the operating boundaries and conditions for reliable integration into a circuit.

Forward Voltage (V_F): Per segment, the forward voltage typically ranges from 2.1V to 2.6V at a drive current of 20 mA. This is a standard range for AlInGaP LEDs. Designers must ensure the driving circuit can provide this voltage. At the recommended low current of 1-10 mA, the actual V_F will be slightly lower, following the diode's I-V curve.

Reverse Current (I_R): The maximum reverse current per segment is 10 \u00b5A at a reverse voltage (V_R) of 5V. This is a leakage specification, important for ensuring the display does not conduct significantly if reverse polarity is accidentally applied, though such an event should be avoided in design.

2.3 Absolute Maximum Ratings

These ratings specify the limits beyond which permanent damage may occur. Operating the device continuously at these limits is not advised.

• Power Dissipation per Segment: 70 mW. This limits the maximum combination of forward current and voltage drop across a segment.
• Peak Forward Current per Segment: 100 mA, but only under pulsed conditions (1/10 duty cycle, 0.1 ms pulse width). This allows for brief periods of high-intensity multiplexing.
• Continuous Forward Current per Segment: 25 mA at 25\u00b0C. This rating derates linearly at 0.33 mA/\u00b0C as ambient temperature (T_a) increases above 25\u00b0C. For example, at 85\u00b0C, the maximum allowable continuous current would be approximately: 25 mA - ((85-25) * 0.33 mA) \u2248 5.2 mA.
• Reverse Voltage per Segment: 5 V.
• Operating & Storage Temperature Range: -35\u00b0C to +85\u00b0C. This wide range makes it suitable for industrial and automotive environments (non-critical areas).
• Solder Temperature: Maximum 260\u00b0C for a maximum of 3 seconds, measured 1.6mm below the seating plane. This is a standard reflow soldering profile guideline.

3. Binning System Explanation

The datasheet indicates the device is \"Categorized for Luminous Intensity.\" This implies a binning or sorting process based on measured light output. While specific bin code details are not provided in this excerpt, typical practice involves testing each unit at a standard current (e.g., 10 mA or 20 mA) and grouping them into bins based on their measured luminous intensity (e.g., Bin A: 450-550 \u00b5cd, Bin B: 550-650 \u00b5cd). This allows manufacturers to purchase displays with guaranteed minimum brightness levels for their application, ensuring consistency across production runs. The 2:1 intensity matching ratio is a separate, related specification that applies within a single device.

4. Performance Curve Analysis

Although the specific graphs are not detailed in the provided text, typical curves for such a device would include:

• I-V (Current-Voltage) Curve: Would show the exponential relationship typical of a diode. At the low recommended operating currents (1-10 mA), the curve is in its steeply rising region, meaning small changes in voltage cause large changes in current. Therefore, constant current driving is highly recommended over constant voltage driving for stable and matched brightness.
• Luminous Intensity vs. Forward Current (I_V vs. I_F): This curve is generally linear over a wide range of currents. The efficiency (lumens per watt or \u00b5cd/mA) may be highest at lower currents and gradually decrease at very high currents due to thermal and efficiency droop effects.
• Forward Voltage vs. Temperature: The forward voltage of an LED has a negative temperature coefficient, meaning it decreases as the junction temperature increases. This is an important consideration for driving circuits, especially those using voltage sources or simple resistors.
• Luminous Intensity vs. Temperature: The light output typically decreases as junction temperature rises. The rate of this decrease is a key reliability parameter.

5. Mechanical & Package Information

The display has a digit height of 0.39 inches (10.0 mm). The package is a standard LED display module format. The physical dimensions are provided in a detailed drawing with all critical measurements in millimeters. Tolerances on these dimensions are typically \u00b10.25 mm unless otherwise specified. The device features a \"gray face and white segments,\" which refers to the color of the plastic housing (gray) and the diffused material forming the segment shapes (white). The white segments help scatter and diffuse the red light from the underlying LED chip, creating a uniform, illuminated segment appearance against the gray, non-illuminated background for high contrast.

6. Pin Connection & Internal Circuit

The LTC-4665JD is configured as a Duplex Common Anode display with a Right Hand Decimal point. This is a critical piece of information for the circuit designer.

• Common Anode: This means the anodes (positive terminals) of the LEDs for each digit are connected together internally. To illuminate a segment, its corresponding cathode pin must be driven low (to ground) while the common anode for that digit is driven high (supplied with positive voltage/current).
• Duplex Arrangement: The pinout shows shared cathode pins for digits 2 and 3 for segments A, C, D, E, F, and G. Digit 1 has some independent cathode pins (B, C). This multiplexing arrangement reduces the total number of pins required to control three digits from 24 (8 segments x 3 digits) down to 11. It requires time-division multiplexing in the driving circuit, where each digit is illuminated one at a time in rapid succession, relying on persistence of vision to make all digits appear continuously lit.
• Pin Functions: The provided table lists the specific function for each of the 11 pins, including common anodes for digit 3 (pin 7) and for digits 1 & 2 (shared on pin 11), and various cathode connections for specific segments across the digits.

7. Soldering & Assembly Guidelines

The key guideline provided is the soldering temperature profile: a maximum peak temperature of 260\u00b0C for no more than 3 seconds, measured 1.6mm below the seating plane (typically the PCB surface). This is compatible with standard lead-free reflow soldering processes (e.g., using SAC305 solder).

General Handling & Storage: While not explicitly stated, standard ESD (Electrostatic Discharge) precautions should be observed during handling, as LEDs are semiconductor devices susceptible to static damage. Storage should be within the specified temperature and humidity ranges to prevent moisture absorption, which can cause \"popcorning\" during reflow.

8. Application Suggestions

8.1 Typical Application Circuits

The most common driving method is multiplexed constant current driving. A microcontroller or dedicated display driver IC would be used. The process involves:

1. Enabling the common anode for Digit 1 (by providing current via a transistor or driver pin).
2. Setting the cathode lines for the segments that need to be ON in Digit 1 to a low state (sinking current).
3. Maintaining this state for a short period (e.g., 1-5 ms).
4. Turning off Digit 1's anode and the segment cathodes.
5. Repeating steps 1-4 for Digit 2, then Digit 3, and cycling continuously.

The average current per segment is the peak current multiplied by the duty cycle (time the digit is active). For example, to achieve an average I_F of 5 mA with a 1/3 duty cycle (typical for 3-digit multiplexing), the peak current during its active time would need to be 15 mA. This must be checked against the maximum continuous current rating, derated for temperature.

8.2 Design Considerations

• Current Limiting: Always use series resistors or, preferably, constant current drivers/sinks to control the segment current. This compensates for variations in forward voltage and ensures consistent brightness.
• Multiplexing Frequency: The refresh rate should be high enough to avoid visible flicker, typically above 60 Hz for the entire display (so each digit refreshed at >180 Hz).
• Viewing Angle: The wide viewing angle is beneficial but consider the final enclosure. A deep bezel or a tinted window may affect perceived brightness and angle.
• Power Sequencing: Ensure no pin is subjected to voltages outside the absolute maximum ratings during power-up or power-down of the system.

9. Technical Comparison & Differentiation

The primary differentiators of the LTC-4665JD are:

• Material Technology (AlInGaP): Compared to older GaAsP or GaP LEDs, AlInGaP offers significantly higher luminous efficiency, resulting in brighter output at the same current or equivalent brightness at much lower current.
• Low Current Operation: Its characterization and testing for excellent low-current performance (down to 1 mA/segment) is a key advantage for battery-powered or energy-sensitive applications. Not all seven-segment displays maintain good intensity matching and appearance at such low currents.
• High Contrast Package: The gray face/white segment design is optimized for contrast, which can be superior to all-red or all-green packages, especially under high ambient light.

10. Frequently Asked Questions (Based on Technical Parameters)

Q: Can I drive this display with a 5V microcontroller pin directly?
A: No, not directly for segment driving. The forward voltage is ~2.4V, and a series resistor is mandatory to limit current. For common anode driving, you would use a PNP transistor or a high-side driver to supply current to the anode, controlled by the MCU. The cathodes can be connected to MCU pins via current-limiting resistors if the MCU can sink the required peak current.

Q: What is the purpose of the \"Duplex\" pin configuration?
A: It minimizes the pin count of the display package, making it physically smaller and cheaper to manufacture. It requires a multiplexing driver circuit, which is standard practice for multi-digit displays.

Q: How do I achieve uniform brightness across all three digits?
A: Ensure the multiplexing duty cycle is equal for each digit. The shared cathode connections for Digits 2 & 3 mean their electrical characteristics are tightly matched. Digit 1, with some independent pins, might have slight variations, but the intensity matching ratio specification ensures it will be within an acceptable range if driven correctly.

Q: Is a heat sink required?
A> For continuous operation at the maximum rated current (25 mA/segment) at elevated ambient temperatures, careful thermal design of the PCB (using thermal relief pads, possibly a ground plane) is necessary. For typical low-current operation (1-10 mA average), no special heat sinking is needed.

11. Practical Design Case Study

Scenario: Designing a portable, battery-operated 3-digit voltmeter with a microcontroller.

Implementation: The microcontroller runs an ADC to measure voltage, converts the value to three digits, and drives the LTC-4665JD. A dedicated port expander or GPIO pins control the 11 display lines. The design uses constant current sink drivers (e.g., a transistor array like ULN2003) for the cathode lines to ensure stable current regardless of V_F variations. The common anodes are driven by PNP transistors. The multiplexing routine runs on a timer interrupt at 200 Hz per digit (600 Hz total refresh). To conserve power, the segment current is set via the current-limiting circuitry to 2 mA average. With a 1/3 duty cycle, the peak current is 6 mA, well within ratings. The gray face provides excellent contrast against the instrument's dark enclosure, and the AlInGaP red is easily visible. The low current draw significantly extends battery life compared to using a display rated for higher currents.

12. Technology Principle Introduction

The core technology is the AlInGaP light-emitting diode. When a forward voltage is applied across the P-N junction of this semiconductor material, electrons and holes recombine in the active region, releasing energy in the form of photons (light). The specific composition of aluminium, indium, gallium, and phosphide determines the bandgap energy, which directly correlates to the wavelength (color) of the emitted light. The use of a non-transparent GaAs substrate helps absorb stray photons that would otherwise be emitted sideways or backwards, improving overall forward light extraction efficiency and contrast. The individual LED chips are wire-bonded and encapsulated within the plastic package, which forms the seven segments. The white diffusing material over each chip spreads the point-source light evenly across the segment area.

13. Technology Trends

While this specific device uses a well-established technology, broader trends in display technology include:

• Increased Efficiency: Ongoing research in semiconductor materials (like improved AlInGaP or emerging materials for other colors) continues to push the lumens-per-watt metric higher, enabling brighter displays or lower power consumption.
• Integration: Trends move towards displays with integrated driver ICs (\"smart displays\") that communicate via serial interfaces (I2C, SPI), simplifying the host controller design and reducing wiring.
• Miniaturization & Resolution: For seven-segment types, the trend is towards smaller digit heights for denser information panels or integration into smaller devices, while maintaining readability.
• Color Options: While this is a red display, full-color programable LED dot matrix and segment displays are becoming more common for more dynamic information presentation, though often at higher cost and complexity than single-color devices like the LTC-4665JD.

The LTC-4665JD represents a mature, optimized solution for applications where reliable, low-power, numeric red display is the primary requirement.