LTC-3698KF LED Display Datasheet - 0.39-inch Digit Height - Yellow Orange Color - 2.6V Forward Voltage - English Technical Document

1. Product Overview

The LTC-3698KF is a solid-state, single-digit alphanumeric display module. Its primary function is to provide clear, highly visible numeric and limited alphabetic character output in electronic devices. The core technology is based on Aluminium Indium Gallium Phosphide (AlInGaP) semiconductor material, which is renowned for producing high-efficiency light emission in the yellow-orange to red spectrum. This specific device utilizes yellow-orange LED chips fabricated on a non-transparent Gallium Arsenide (GaAs) substrate. The display features a light gray faceplate with white segments, a combination designed to maximize contrast and readability under various lighting conditions. Its compact 0.39-inch digit height makes it suitable for applications where space is at a premium but legibility is critical.

1.1 Core Advantages and Target Market

The device offers several key advantages that define its position in the market. It provides high brightness and excellent contrast, ensuring visibility even in brightly lit environments. The wide viewing angle is a significant benefit, allowing the display to be read from various positions without significant loss of clarity. As a solid-state device, it offers superior reliability and longevity compared to older technologies like filament-based displays, with no moving parts to wear out. Its low power requirement makes it ideal for battery-operated or energy-conscious applications. The device is categorized for luminous intensity and is offered in a lead-free package compliant with RoHS directives, addressing environmental regulations. Typical target markets include industrial instrumentation (e.g., panel meters, test equipment), consumer appliances (e.g., microwave ovens, coffee makers), automotive auxiliary displays, and various embedded systems requiring a reliable numeric readout.

2. In-Depth Technical Parameter Analysis

The electrical and optical parameters define the operational boundaries and performance of the display. A thorough understanding is essential for proper circuit design and integration.

2.1 Absolute Maximum Ratings

These ratings specify the limits beyond which permanent damage to the device may occur. They are not for continuous operation.

• Power Dissipation per Chip: 70 mW. This is the maximum power that can be safely dissipated by an individual LED segment chip as heat.
• Peak Forward Current per Chip: 60 mA. This current is allowed only under pulsed conditions with a 1/10 duty cycle and a 0.1 ms pulse width. It is useful for multiplexing schemes or achieving momentary higher brightness.
• Continuous Forward Current per Chip: The rating is 25 mA at 25°C. Crucially, this rating derates linearly at a rate of 0.28 mA/°C as the ambient temperature (Ta) increases above 25°C. For example, at 85°C, the maximum allowable continuous current would be approximately: 25 mA - ((85°C - 25°C) * 0.28 mA/°C) = 8.2 mA. This derating is critical for thermal management and long-term reliability.
• Operating & Storage Temperature Range: -35°C to +105°C. The device can withstand and operate within this broad temperature range.
• Solder Temperature: Maximum 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane. This defines the reflow soldering profile constraints.

2.2 Optical & Electrical Characteristics (Typical @ 25°C)

These parameters describe the device's performance under normal operating conditions.

• Average Luminous Intensity (Iv): 500 (Min), 1300 (Typ), μcd (Microcandelas) at a forward current (IF) of 1 mA. This is the measure of perceived light output. The wide range indicates a binning process; designers must account for the minimum value for worst-case visibility.
• Peak Emission Wavelength (λp): 611 nm (Typical) at IF=20mA. This is the wavelength at which the spectral power distribution is maximum.
• Spectral Line Half-Width (Δλ): 17 nm (Typical) at IF=20mA. This indicates the spectral purity; a smaller value means a more monochromatic light.
• Dominant Wavelength (λd): 605 nm (Typical) at IF=20mA. This is the single wavelength perceived by the human eye, defining the yellow-orange color.
• Forward Voltage per Segment (VF): 2.05 (Min), 2.6 (Typical) Volts at IF=20mA. This is critical for designing the current-limiting circuitry. The driver must supply enough voltage to overcome this drop.
• Reverse Current per Segment (IR): 100 μA (Max) at a Reverse Voltage (VR) of 5V. The datasheet explicitly notes this parameter is for test purposes only, and the device should not be continuously operated under reverse bias.
• Luminous Intensity Matching Ratio (Iv-m): 1.6:1 (Max) at IF=1mA. This is a crucial specification for display uniformity. It means the brightest segment will be no more than 1.6 times brighter than the dimmest segment within the same digit, ensuring a consistent appearance.
• Cross Talk: ≤ 2.5%. This specifies the maximum amount of unintended light leakage from an unpowered segment when an adjacent segment is illuminated.

3. Binning System Explanation

The datasheet indicates the device is \"categorized for luminous intensity.\" This implies a binning process where manufactured units are sorted based on measured light output (Iv) at a standard test current (1mA). The specified range of 500 to 1300 μcd likely represents the spread across different bins available. Designers can select a specific bin for applications requiring tight brightness matching between multiple displays. The 1.6:1 intensity matching ratio within a single unit is a separate, guaranteed performance parameter for segment-to-segment uniformity.

4. Performance Curve Analysis

While the PDF references typical characteristic curves, the provided text does not include the actual graphs. Based on standard LED behavior, these curves would typically include:

• Current vs. Forward Voltage (I-V Curve): Shows the exponential relationship. The forward voltage (VF) increases with current and has a negative temperature coefficient (decreases as temperature rises).
• Luminous Intensity vs. Forward Current (L-I Curve): Shows that light output is approximately linear with current at lower currents but may saturate at higher currents due to thermal and efficiency droop.
• Luminous Intensity vs. Ambient Temperature: Demonstrates how light output decreases as the junction temperature increases. This is linked to the current derating requirement.
• Spectral Distribution: A plot of relative intensity vs. wavelength, showing the peak at ~611nm and the half-width of ~17nm.

Designers should consult the full datasheet for these graphs to accurately model performance under non-standard conditions.

5. Mechanical and Package Information

5.1 Package Dimensions and Tolerances

The display has a digit height of 0.39 inches (9.8 mm). All dimensional tolerances are ±0.25mm unless otherwise specified. Key mechanical notes include: pin tip shift tolerance of ±0.4mm, limits on foreign material and ink contamination on the segment surface, a limit on reflector bending (≤1% of length), and a limit on bubbles within the segment material. The datasheet recommends a PCB hole diameter of 1.0 mm for the leads.

5.2 Pin Connection and Circuit Diagram

The device has a 16-pin footprint, though not all positions have physical pins or electrical connections. It is configured as a Common Anode display. The internal circuit diagram shows that the anodes for each digit (Digit 1, 2, 3) are connected together internally per digit. Each segment cathode (A, B, C, D, E, F, G, and L/L1/L2 for the decimal points/indicators) is brought out to a separate pin. This architecture is optimal for multiplexed driving, where a microcontroller sequentially energizes each digit's common anode while presenting the pattern for that digit on the shared cathode lines.

Pinout Summary: Pin 2: Common Anode Digit 1; Pin 6: Common Anode Digit 2; Pin 8: Common Anode Digit 3. Cathodes: Pin 3 (E), 4 (C), 5 (D), 7 (L/L1/L2), 9 (G), 12 (B), 15 (A), 16 (F). Pins 1, 10, 11, 13, 14 are noted as \"No Connection and No Pin.\"

6. Soldering and Assembly Guidelines

The key assembly specification is the solder temperature profile: a maximum of 260°C for a maximum of 3 seconds, measured 1.6mm below the seating plane of the package. This is a standard lead-free reflow soldering requirement. Designers must ensure their PCB assembly process adheres to this limit to prevent damage to the internal LED chips or the plastic package. The recommended 1.0mm PCB hole diameter aids in proper lead insertion and solder wicking. Standard ESD (Electrostatic Discharge) precautions should be observed during handling. For storage, the specified temperature range of -35°C to +105°C applies.

7. Application Suggestions and Design Considerations

7.1 Typical Application Circuits

The most common drive method is multiplexing. A microcontroller or dedicated display driver IC would have three output lines to control the three common anodes (via transistors, as the current for an entire digit can be significant) and eight output lines to control the segment cathodes (typically via current-limiting resistors or a constant-current driver). The microcontroller rapidly cycles through each digit, turning on its anode and enabling the cathodes for the segments that should be lit for that digit. The persistence of vision creates the illusion of a stable, three-digit display.

7.2 Critical Design Considerations

• Current Limiting: External resistors are mandatory for each cathode line (or a constant-current driver) to set the forward current (IF) for the segments. The value is calculated based on the supply voltage (Vcc), the LED forward voltage (VF ~2.6V), and the desired current (e.g., 10-20 mA for good brightness, respecting the derating curve).
• Thermal Management: The current derating with temperature is vital. In high ambient temperature environments or enclosures with poor ventilation, the maximum continuous current must be reduced accordingly to prevent overheating and accelerated degradation.
• Multiplexing Frequency: Must be high enough to avoid visible flicker (typically >60 Hz per digit). The duty cycle affects perceived brightness; average current must be considered for power and thermal calculations.
• Viewing Angle: The wide viewing angle is an advantage, but the mounting position should still be considered relative to the intended user.

8. Technical Comparison and Differentiation

Compared to older technologies like vacuum fluorescent displays (VFDs) or incandescent displays, the AlInGaP LED offers significantly lower power consumption, higher reliability, and insensitivity to vibration. Compared to standard red GaAsP LEDs, AlInGaP technology provides much higher luminous efficiency (more light per mA) and better stability over temperature and time. The specific combination of a light gray face with white segments in this device enhances contrast compared to all-red or all-green displays with a black face, potentially improving readability in certain conditions.

9. Frequently Asked Questions (Based on Technical Parameters)

Q: What is the purpose of the \"No Connection and No Pin\" positions?
A: This is often done to maintain a standard physical footprint or pin spacing that may be shared with other display variants in a product family, even if some pins are not electrically used in this specific model. It ensures mechanical compatibility.

Q: How do I interpret the Luminous Intensity Matching Ratio of 1.6:1?
A: This guarantees visual uniformity. If you measure all segments of one digit at the same current, the dimmest segment will have an intensity of \"X,\" and the brightest segment will have an intensity no greater than \"1.6 * X.\" A lower ratio indicates better uniformity.

Q: Can I drive this display with a 5V microcontroller directly?
A: No. You must use external components. The microcontroller GPIO pins cannot source/sink enough current for the LEDs (especially the common anode current for a whole digit). Furthermore, you need current-limiting resistors in series with each cathode. The circuit requires transistors (e.g., NPN/PNP or MOSFETs) to switch the higher current for the common anodes.

10. Practical Application Example

Scenario: Designing a simple 3-digit voltmeter display. A microcontroller with an analog-to-digital converter (ADC) measures a voltage. The firmware converts this reading to three decimal digits. Using a multiplexing routine, the microcontroller would: 1) Turn off all digit anode drivers. 2) Output the segment pattern for the \"hundreds\" digit on the cathode lines (e.g., to display \"1\\