LTST-C191KRKT-5A SMD LED Datasheet - 0.55mm Height - 2.0V Typical Forward Voltage - 75mW Power Dissipation - Red Color - English Technical Document

1. Product Overview

The LTST-C191KRKT-5A is a surface-mount device (SMD) light-emitting diode (LED) designed for modern, compact electronic applications. Its primary defining characteristic is an exceptionally low profile, with a package height of just 0.55 millimeters. This makes it ideal for applications where space constraints are critical, such as in ultra-thin displays, mobile devices, and backlighting modules. The device utilizes an AlInGaP (Aluminum Indium Gallium Phosphide) semiconductor material for the light-emitting chip, which is known for producing high-efficiency red light. The LED is supplied on industry-standard 8mm tape mounted on 7-inch diameter reels, facilitating high-speed automated pick-and-place assembly processes. It is fully compliant with RoHS (Restriction of Hazardous Substances) directives, classifying it as a green product.

2. Technical Parameter Deep-Dive

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under or at these limits is not guaranteed. Key parameters include a maximum power dissipation of 75 milliwatts (mW) at an ambient temperature (Ta) of 25°C. The maximum continuous forward current (DC) is rated at 30 mA. For pulsed operation, a peak forward current of 80 mA is permissible under specific conditions: a 1/10 duty cycle and a pulse width of 0.1 milliseconds. The device can withstand a reverse voltage of up to 5 volts. The operating temperature range is from -30°C to +85°C, while the storage temperature range is slightly wider at -40°C to +85°C. A critical rating for assembly is the infrared soldering condition, which specifies the LED can tolerate a peak temperature of 260°C for a maximum of 5 seconds.

2.2 Electro-Optical Characteristics

These characteristics are measured at a standard test condition of Ta=25°C and a forward current (IF) of 5 mA, unless otherwise noted. The luminous intensity (Iv), a measure of perceived brightness, has a typical value but is binned with minimums ranging from 7.1 mcd to 28.0 mcd (see Section 3). The viewing angle (2θ1/2), defined as the full angle at which intensity drops to half its axial value, is a wide 130 degrees, providing a broad emission pattern. The peak emission wavelength (λP) is typically 639 nanometers (nm), while the dominant wavelength (λd), which defines the perceived color, is 630 nm. The spectral bandwidth (Δλ) is approximately 20 nm. The forward voltage (VF) at 5 mA has a typical value of 2.0 volts, with a range from 1.6V to 2.2V, and is also subject to binning. The reverse current (IR) is a maximum of 10 microamperes at 5V reverse bias, and the junction capacitance (C) is typically 40 picofarads.

3. Binning System Explanation

To ensure consistency in mass production, LEDs are sorted into performance bins. The LTST-C191KRKT-5A uses a two-dimensional binning system.

3.1 Forward Voltage Binning

Forward voltage is binned into six codes (1 through 6). Each bin represents a 0.1-volt range, starting from 1.6-1.7V for Bin 1 up to 2.1-2.2V for Bin 6. A tolerance of ±0.1V is applied to each bin. This allows designers to select LEDs with closely matched VF for applications where uniform current sharing in parallel connections is important.

3.2 Luminous Intensity Binning

Luminous intensity is binned into four codes: K, L, M, and N. Bin K covers intensities from 7.10 to 11.2 millicandelas (mcd), Bin L from 11.2 to 18.0 mcd, Bin M from 18.0 to 28.0 mcd, and Bin N from 28.0 to 45.0 mcd, all measured at IF=5mA. A tolerance of ±15% is applied to each intensity bin. This system enables selection based on required brightness levels, helping to achieve uniform appearance in multi-LED arrays.

4. Performance Curve Analysis

While specific graphical curves are referenced in the datasheet (e.g., Figure 1 for spectral distribution, Figure 6 for viewing angle), their trends can be described. The relationship between forward current (IF) and forward voltage (VF) is non-linear and follows the typical diode exponential characteristic. The luminous intensity is approximately proportional to the forward current within the operating range. The peak wavelength (λP) and dominant wavelength (λd) may exhibit a slight negative temperature coefficient, meaning they can shift towards longer wavelengths (red-shift) as the junction temperature increases. The forward voltage typically decreases with increasing temperature.

5. Mechanical and Package Information

5.1 Package Dimensions

The LED features an industry-standard EIA package footprint. The key dimension is the ultra-low height of 0.55 mm. Detailed mechanical drawings specify the length, width, lead spacing, and other critical dimensions, all with a standard tolerance of ±0.10 mm unless otherwise noted. The lens is water-clear, allowing the native red color of the AlInGaP chip to be emitted without diffusion.

5.2 Polarity Identification and Pad Design

The datasheet includes a suggested soldering pad layout (land pattern) for PCB design. This pattern is optimized for reliable solder joint formation and mechanical stability during reflow. The cathode is typically identified by a visual marker on the LED package, such as a notch, a green dot, or a cut corner on the lens. Correct polarity alignment is crucial for device operation.

6. Soldering and Assembly Guide

6.1 Reflow Soldering Profiles

The device is compatible with both infrared (IR) and vapor phase reflow processes. Two suggested reflow profiles are provided: one for standard (tin-lead) solder paste and another for lead-free (SnAgCu) solder paste. The lead-free profile is more demanding, requiring careful control of the preheat, soak, reflow, and cooling phases to prevent thermal shock while ensuring a proper solder joint. The absolute maximum condition for the LED itself is 260°C peak temperature for 5 seconds.

6.2 Storage and Handling

LEDs should be stored in an environment not exceeding 30°C and 70% relative humidity. Once removed from their original moisture-barrier packaging, it is recommended to complete the IR reflow soldering process within 672 hours (28 days). For longer storage outside the original bag, LEDs should be kept in a sealed container with desiccant or in a nitrogen atmosphere. Components stored beyond 672 hours may require a baking procedure (e.g., 60°C for 24 hours) to remove absorbed moisture and prevent \"popcorning\" during reflow.

6.3 Cleaning

If cleaning after soldering is necessary, only specified solvents should be used. Immersing the LED in ethyl alcohol or isopropyl alcohol at room temperature for less than one minute is acceptable. The use of unspecified or aggressive chemical cleaners can damage the plastic lens and package.

7. Packaging and Ordering Information

The standard packaging is 8mm wide embossed carrier tape on 7-inch (178mm) diameter reels. Each reel contains 5000 pieces of the LTST-C191KRKT-5A LED. The tape pockets are sealed with a protective top cover tape. Packaging follows the ANSI/EIA 481-1-A-1994 standard. For quantities less than a full reel, a minimum packing quantity of 500 pieces applies for remainder parts.

8. Application Recommendations

8.1 Typical Application Circuits

LEDs are current-driven devices. To ensure uniform brightness when driving multiple LEDs in parallel, it is strongly recommended to use a individual current-limiting resistor in series with each LED. A common circuit mistake is connecting multiple LEDs directly in parallel to a single current source (Circuit B in the datasheet). Due to natural variations in the forward voltage (VF) characteristic between individual LEDs, this can lead to severe current imbalance, where one LED may draw most of the current and overheat, while others remain dim. The series resistor for each LED helps stabilize the current and promote uniform illumination.

8.2 Electrostatic Discharge (ESD) Protection

The LED is sensitive to electrostatic discharge. Precautions must be taken during handling and assembly: personnel should wear grounded wrist straps or anti-static gloves; all workstations, equipment, and storage racks must be properly grounded; and an ionizer can be used to neutralize static charge that may accumulate on the plastic lens. ESD damage may not be immediately visible but can degrade performance or cause premature failure.

9. Technical Comparison and Differentiation

The primary differentiating advantage of the LTST-C191KRKT-5A is its 0.55mm profile, which is significantly thinner than many standard SMD LEDs (e.g., 0603 or 0805 packages which are often over 0.8mm tall). The use of AlInGaP technology provides higher luminous efficiency for red light compared to older technologies like GaAsP, resulting in brighter output for the same drive current. The wide 130-degree viewing angle is another benefit for applications requiring broad-area illumination rather than a focused beam.

10. Frequently Asked Questions (FAQ)

Q: Can I drive this LED without a series resistor?
A: It is not recommended. Driving an LED directly from a voltage source without current limiting will likely destroy it due to excessive current. Always use a series resistor or a constant-current driver.

Q: What is the difference between peak wavelength and dominant wavelength?
A: Peak wavelength (λP) is the wavelength at which the spectral power output is highest. Dominant wavelength (λd) is derived from the color coordinates and represents the single wavelength of a pure monochromatic light that would be perceived as the same color by the human eye. λd is more relevant for color specification.

Q: How do I interpret the bin code in the part number?
A: The part number LTST-C191KRKT-5A contains bin information. The \"KRKT\" segment typically encodes the intensity and voltage bin codes. Refer to the bin code list in the datasheet to understand the specific performance range of the ordered part.

11. Practical Design Case Study

Consider designing a status indicator panel for a portable medical device. Space is extremely limited, and the panel must be readable from various angles. The 0.55mm height of the LTST-C191KRKT-5A allows it to fit behind a thin front bezel. Selecting LEDs from the same intensity bin (e.g., all from Bin \"M\") ensures all indicator lights have uniform brightness. Using a series resistor for each LED, calculated based on the supply voltage and the typical VF of 2.0V at the desired current (e.g., 5-10 mA), guarantees stable operation and longevity. The wide 130-degree viewing angle ensures the indicator is visible even when the device is viewed off-axis.

12. Operating Principle Introduction

An LED is a semiconductor p-n junction diode. When a forward voltage is applied, electrons from the n-type region and holes from the p-type region are injected into the junction region. When these charge carriers recombine, energy is released in the form of photons (light). The specific semiconductor material (AlInGaP in this case) determines the bandgap energy, which in turn dictates the wavelength (color) of the emitted light. A red AlInGaP LED has a bandgap energy corresponding to photons in the red portion of the visible spectrum (~630-640 nm).

13. Technology Trends

The trend in SMD LEDs for consumer and industrial electronics continues towards miniaturization, higher efficiency, and improved reliability. Package heights are decreasing to enable thinner end products. Efficiency improvements (more light output per watt of electrical input) are driven by advances in chip design, epitaxial growth, and package extraction efficiency. There is also a focus on enhancing color consistency and stability over temperature and lifetime. The adoption of lead-free and high-temperature compatible materials in packaging is standard to meet environmental regulations and withstand demanding assembly processes.