SMD RGB LED with Embedded Driver - LTSA-E27CQEGBW Datasheet - English Technical Document

1. Product Overview

The LTSA-E27CQEGBW is a high-performance, surface-mount RGB LED module designed for automated assembly and space-constrained applications. It integrates individual AlInGaP red, InGaN green, and InGaN blue LED chips within a single, compact package. A key differentiator of this product is the inclusion of an embedded 8-16 bit, 3-channel constant-current driver and control IC, which provides advanced features such as PWM dimming control, temperature compensation, and serial data communication. This integration simplifies system design by reducing external component count and PCB footprint.

The module is housed in a diffused lens package, which helps to blend the light from the individual color chips to produce a more uniform color output and wider viewing angle. It is supplied on 8mm tape mounted on 7-inch diameter reels, making it fully compatible with high-speed automated pick-and-place assembly equipment. The device is designed to meet RoHS compliance standards and is preconditioned to JEDEC Level 2 for enhanced reliability.

1.1 Core Features and Advantages

• Integrated Driver IC: Eliminates the need for external current-limiting resistors and driver circuits for each color channel. The embedded IC provides precise current control up to 60mA per channel.
• Advanced Control: Supports 7-bit current adjustment per channel and up to 16-bit PWM (Pulse Width Modulation) for smooth, high-resolution dimming and color mixing.
• Temperature Compensation: Features a built-in diagnostic function that measures the LED junction temperature. This data is used by an internal algorithm to automatically adjust the drive current for the red LED chip, maintaining consistent luminous intensity and color point over a wide operating temperature range (-40°C to +110°C).
• Robust Communication: Utilizes a serial communication interface (Clock Input/Output, Data Input/Output) with CRC (Cyclic Redundancy Check) protection for reliable data transmission, especially in cascaded configurations or noisy environments.
• System Protection: Includes a watchdog timer function to prevent LED flickering that can be caused by hot-plug events or communication errors.
• Low Power Modes: Supports a sleep mode for reduced standby power consumption, which is critical for battery-powered or energy-efficient applications.
• Automotive Grade: Designed with reference to AEC-Q102 guidelines for discrete optoelectronic semiconductors and classified for corrosion robustness (Class 1B), making it suitable for certain automotive accessory applications.

1.2 Target Applications and Markets

This LED is engineered for applications requiring reliable, compact, and intelligent multi-color lighting solutions. Its primary target markets include:

• Consumer Electronics: Status indicators, backlighting, and decorative lighting in devices such as smartphones, tablets, laptops, gaming peripherals, and home appliances.
• Professional and Industrial Equipment: Panel indicators, machine status lights, and human-machine interface (HMI) feedback in network systems, control panels, and test equipment.
• Automotive Interior Lighting: Non-critical interior lighting applications such as ambient lighting, dashboard backlighting, and accessory status indicators, benefiting from its temperature stability and robust communication.
• Signage and Display: Low-resolution indoor signboard applications, point-of-sale displays, and decorative architectural lighting where color-changing capabilities are desired.

2. Technical Parameter Analysis

The following section provides a detailed, objective analysis of the key electrical, optical, and thermal parameters specified in the datasheet. Understanding these parameters is crucial for proper circuit design and performance prediction.

2.1 Absolute Maximum Ratings

These ratings define the stress limits beyond which permanent damage to the device may occur. Operation under these conditions is not guaranteed.

• IC Supply Voltage (VDD): 5.5V maximum. Exceeding this voltage can damage the internal control circuitry.
• LED Output Current (Iout): 60mA maximum per channel. This is the absolute peak current the output driver can handle; typical operating currents are lower.
• Junction Temperature (Tj): 125°C maximum. The temperature of the semiconductor junction inside the LED or IC must not exceed this limit.
• Operating/Storage Temperature: -40°C to +110°C. The device can be stored and operated within this full range.
• Infrared Reflow Soldering: Withstands a peak temperature of 260°C for a maximum of 10 seconds, which is standard for lead-free (Pb-free) solder processes.

2.2 Electrical and Optical Characteristics

These parameters are measured under typical conditions (Ta=25°C, VDD=5V, 8-bit PWM setting at maximum color value) and define the expected performance.

• Supply Voltage (VDD): Recommended operating range is 3.3V to 5.5V, with a typical value of 5.0V.
• Forward Current (If): The typical drive currents for each color at maximum brightness are: Red: 30mA, Green: 46mA, Blue: 20mA. These values are set by the internal driver and can be adjusted via the 7-bit current control register.
• Luminous Intensity (Iv): The typical axial luminous intensity for each primary color at maximum current is: Red: 950 mcd, Green: 2170 mcd, Blue: 380 mcd. The minimum and maximum values indicate the expected production spread. The calibrated white point (combining all three colors) has a typical intensity of 3500 mcd.
• Dominant Wavelength (λd): Defines the perceived color of each LED. Typical values are: Red: 620 nm, Green: 525 nm, Blue: 465 nm.
• Chromaticity Coordinates (x, y): For the calibrated white point, the target coordinates are x=0.3127, y=0.3290, which corresponds to the standard D65 white point, often used as a reference for display and lighting.
• Viewing Angle (2θ1/2): 120 degrees. This is the full angle at which the luminous intensity drops to half of its axial value. The diffused lens contributes to this wide viewing angle.

2.3 Thermal Characteristics

Thermal management is critical for LED longevity and performance stability.

• Thermal Resistance, Junction-to-Solder Point (Rth JS): Two values are provided: Rth JSelec = 63 K/W and Rth JSreal = 73 K/W. The \"elec\" value is typically derived from an electrical measurement method, while the \"real\" value may represent a more conservative or practical thermal path estimate. These values indicate how effectively heat travels from the LED junction to the solder points on the PCB. A lower value is better. For example, if the LED is dissipating 0.2W, the junction temperature rise above the solder point would be approximately 0.2W * 73 K/W = 14.6°C.

3. Binning and Color Consistency

The datasheet references a bin rank system based on the D65 white point with a tolerance of 3 MacAdam ellipses (3-step). This is a standard method in the lighting industry to define color consistency.

• MacAdam Ellipses: A MacAdam ellipse on a chromaticity diagram represents a zone within which the human eye perceives no color difference under standard viewing conditions. A \"3-step\" ellipse means the color variation is three times the size of the smallest perceptible difference (a 1-step ellipse).
• Implication: All LTSA-E27CQEGBW units from the same production batch (or specified bin) will produce a white light whose color coordinates fall within a 3-step MacAdam ellipse around the D65 point (x=0.3127, y=0.3290). This ensures good color uniformity between different LEDs in an array or system, which is vital for applications like backlighting or multi-LED signage where color mismatch would be noticeable.

4. Performance Curve Analysis

The typical performance curves provide insight into how the device behaves under varying conditions.

4.1 Spectral Distribution

The Relative Intensity vs. Wavelength graph (Fig.1) shows the light output spectrum for each color chip (Red, Green, Blue). Key observations include the narrow, well-defined peaks characteristic of modern LED semiconductors. The red AlInGaP chip typically shows a peak around 620nm, the green InGaN around 525nm, and the blue InGaN around 465nm. The width of these peaks (Full Width at Half Maximum, or FWHM) influences color purity.

3.2 Temperature vs. Performance

The Max. Color Setpoint Vs Temperature curve (Fig.2) likely illustrates how the maximum achievable PWM duty cycle or current setpoint for stable operation may change with ambient temperature. This graph is essential for designing systems that operate reliably across the full temperature range, ensuring the driver IC does not enter thermal shutdown or reduce output prematurely.

4.3 Spatial Radiation Pattern

The Spatial Distribution plot (Fig.3) visually represents the 120-degree viewing angle. It shows how light intensity is distributed as a function of the angle from the central axis (0 degrees). The diffused lens creates a Lambertian or near-Lambertian pattern, where intensity is highest at the center and decreases smoothly towards the edges, providing uniform off-axis visibility.

5. Mechanical and Package Information

5.1 Package Dimensions and Tolerances

The device conforms to a standard SMD footprint. All critical dimensions are provided in millimeters. The general tolerance for package dimensions is ±0.2 mm unless a specific feature has a different callout. Designers must refer to the detailed mechanical drawing in the datasheet for precise pad layout, component height, and lens dimensions to ensure proper PCB land pattern design and clearance for surrounding components.

5.2 Pin Configuration and Function

The 8-pin device has the following pinout and functions:
1. LED VDD: Power supply input for the LED anode common connection. Must be supplied alongside pin 7.
2. CKO: Clock Signal Output for cascading devices.
3. DAO: Serial Data Output for cascading.
4. VPP: High-voltage supply (9-10V) for One-Time Programmable (OTP) memory programming. Held at 5V for read/standby.
5. CKI: Clock Signal Input.
6. DAI: Serial Data Input.
7. VDD: Primary supply voltage (3.3-5.5V) for the internal IC.
8. GND: Ground reference.
Critical Note: Both LED VDD (pin 1) and VDD (pin 7) must be powered simultaneously for correct operation.

6. Soldering and Assembly Guidelines

6.1 Recommended Reflow Profile

The datasheet provides a suggested infrared reflow soldering profile for lead-free (Pb-free) processes. Key parameters typically include:
- Preheat: A gradual ramp to activate flux and minimize thermal shock.
- Soak (Thermal Stabilization): A plateau to ensure even heating of the PCB and component.
- Reflow: The peak temperature zone, where the datasheet specifies a maximum of 260°C for up to 10 seconds (measured at the component leads). This is a standard JEDEC profile for moisture-sensitive devices.
- Cooling: A controlled cool-down period to solidify the solder joints properly.
It is imperative to follow this profile to prevent damage to the LED package, lens, or internal wire bonds from excessive heat or thermal stress.

6.2 Pick-and-Place and Handling

The device is supplied on 8mm tape on 7\" reels, compatible with standard SMT assembly equipment. The thin profile (0.65mm typical) requires careful handling to avoid mechanical stress. Vacuum nozzles of appropriate size and pressure should be used during pick-and-place to prevent damage to the lens or body. The recommended tools for this process are specified in the datasheet revision notes.

7. Functional Description and Application Circuit

7.1 Internal Block Diagram and Principle

The core of the module is a three-channel constant-current sink driver. Each channel independently regulates the current flowing through its respective LED (Red, Green, Blue) to the programmed value, regardless of variations in the forward voltage (Vf) of the LED chips. This ensures consistent color output across different units and over time. The current level for each channel is set via a 7-bit register (allowing 128 discrete current levels). Dimming and color mixing are achieved through a high-resolution 16-bit PWM controller for each channel, providing over 65,000 brightness steps for extremely smooth transitions.

7.2 Typical Application Circuit

A basic application circuit requires:
1. A stable 3.3V to 5.5V supply connected to both VDD (pin 7) and LED VDD (pin 1).
2. A 0.1µF bypass capacitor placed as close as possible between the VDD pin (7) and GND (pin 8) to filter high-frequency noise and ensure stable IC operation.
3. For the serial communication lines (CKI and DAI), it is recommended to reserve space for small RC low-pass filter networks (resistor and capacitor to ground) on the PCB. These filters help to clean up signal integrity in electrically noisy environments or with long trace lengths. The exact component values should be determined based on the specific system's clock frequency and noise characteristics.
4. The VPP pin (4) must be connected to a voltage source. For normal operation (reading OTP, standby), it can be tied to 5V. To program the OTP memory (for storing default settings like color calibration), a voltage between 9.0V and 10.0V must be applied to this pin during the programming sequence.

7.3 Data Communication and Cascading

The device uses a synchronous serial protocol. To control it, a microcontroller must send 56-bit data frames. There are two main frame types, selected by a 3-bit Command field:
- PWM Data (CMD=001): This 56-bit frame contains the 16-bit PWM values for each of the three color channels (48 bits total), plus command and CRC bits. This data controls the instantaneous brightness.
- Primary Register Data (CMD=010): This frame programs the device's configuration registers, settings like global current limits, PWM configuration, and enabling features like temperature compensation or sleep mode.
Multiple devices can be daisy-chained by connecting the DAO and CKO of the first device to the DAI and CKI of the next. A single data stream is sent to the first device, and it passes through the chain. All devices in the chain latch their new data simultaneously when the clock line (CKI) is held high for more than 150 microseconds (the latch signal).

8. Design Considerations and Application Notes

8.1 Thermal Management

Despite the integrated driver, heat dissipation remains crucial. The thermal resistance from junction to solder point (Rth JS) is provided. Designers must calculate the expected power dissipation (P_diss = Vf_Red * I_Red + Vf_Green * I_Green + Vf_Blue * I_Blue + (VDD * I_IC)) and ensure the PCB provides an adequate thermal path (using thermal vias, copper pours) to keep the junction temperature (Tj) well below the 125°C maximum, ideally below 85°C for long-term reliability. The built-in temperature sensor and compensation for the red LED help maintain optical performance but do not eliminate the need for good physical thermal design.

8.2 Power Supply Sequencing and Decoupling

The requirement to power both VDD and LED VDD together is critical. A power-up sequence where one is enabled before the other could place the internal IC or LEDs in an undefined state, potentially causing latch-up or damage. The 0.1µF bypass capacitor on VDD is not optional; it is necessary to prevent voltage droops during fast PWM switching, which could cause the IC to reset or behave erratically.

8.3 Signal Integrity for Cascading

When cascading many devices, signal degradation along the clock and data lines can occur. The recommended RC filters on the CKI and DAI inputs of each device help to suppress ringing and noise. For very long chains or high clock speeds, additional measures like proper impedance matching, shorter traces, or buffer chips may be necessary to ensure reliable communication to the last device in the chain.

9. Comparison and Differentiation

Compared to a standard RGB LED without a driver, the LTSA-E27CQEGBW offers significant advantages:
- Simplified Design: No external current-setting resistors or transistor drivers are needed for each channel.
- Precision and Consistency: The constant-current driver ensures identical current in each LED, leading to more consistent color and brightness from unit to unit, independent of minor Vf variations.
- Advanced Features: Integrated temperature compensation, high-resolution PWM, and serial control are features typically found only in external driver ICs, not in the LED package itself.
- Reduced Component Count and Board Space: Integrates the driver functionality into the LED footprint, saving valuable PCB real estate.
The trade-off is increased complexity in the control software (managing the serial protocol) and a slightly higher component cost compared to a basic LED.

10. Frequently Asked Questions (FAQ)

Q1: Can I drive this LED with a simple microcontroller GPIO pin and a resistor?
A: No. The LED anodes are connected internally to the driver IC's current sinks. You must provide power to the LED VDD pin and control the device via its serial interface (CKI, DAI). Direct connection to GPIO will not work and may damage the device.

Q2: What is the purpose of the OTP memory?
A: The One-Time Programmable memory allows you to store default configuration settings (like initial brightness, color calibration offsets, or function enables) permanently inside the LED module. When power is applied, the IC can read these settings from OTP and configure itself automatically, reducing the initialization code required in the host microcontroller.

Q3: How do I calculate the total power consumption?
A: You need to consider both the LED power and the IC power. For LEDs: P_led = (Avg_Current_Red * Vf_Red) + (Avg_Current_Green * Vf_Green) + (Avg_Current_Blue * Vf_Blue). Vf can be estimated from the IV curve or typical values for the chip technology (~2.0V for Red AlInGaP, ~3.2V for Green/Blue InGaN). For the IC: P_ic ≈ VDD * I_q (quiescent current, from application notes). The average currents depend on your PWM duty cycles.

Q4: Is a heat sink required?
A: For most low-to-medium duty cycle applications at room temperature, the thermal path through the PCB solder pads is sufficient. However, for applications running all three LEDs at full brightness continuously, or in high ambient temperatures, careful thermal design of the PCB (thermal vias, copper area) is essential. A separate metal heat sink is not typically attached directly to this SMD package.