Enhanced LED Driver Solution: Fully Configurable Smart 16 LED Light Source Driver

LED1642GW is ST's next-generation LED array driver, adding a series of fully configurable innovative features, while retaining the original 24-pin standard package, requiring only an external resistor in practical applications, which can significantly reduce component costs and improve System design flexibility.

New embedded features make system design more flexible, providing users with different configuration options: local dimming, global current regulation, switching time setting, inter-channel sequential delay, advanced LED fault detection report, automatic energy saving patent Technology, serial data and clock resynchronization and many other features.

The LED1642GW is designed to meet the noise reduction requirements of the application area shown in Figure 1, allowing the user to set the switching speed of the output channel through the serial interface. A total of four speeds are available, and the on-time setting range is 30nS-270nS. With the combination of the channel output delay, the switch time setting allows the user to easily adjust the application, effectively reduce EMI interference and maximize voltage stability. When the output channel is set to off and the module automatically wakes up after receiving the first channel conduction command, the automatic power saving and energy saving innovation function can automatically turn off the driver.

Figure 1 – Main application example of ALED1642GW

Foreword

The large-scale popularity of LEDs in our daily lives is no longer new, mobile applications, advertising signs, LCD TV backlights, lighting and automotive LED lights are everywhere. LED lamps are lower in price and energy efficiency is rising, giving equipment manufacturers the power to redesign their products. Each product requires a different LED driver.

In the mature LED driver market, suppliers must continually optimize product performance, reliability and cost structure. For important projects with high requirements and high cost, in order to achieve true differentiation and achieve the best performance at the same level, functional innovation must be realized in a clever way to create added value at market prices.

The LED1642GW standard LED driver features excellent channel-to-channel output current matching (±3%), and each product has the industry's smallest operating current. The LED1642GW has an automotive-grade quality certificate to ensure a high level of reliability and robustness. The LED1642GW intelligently handles new market demands and integrates many innovative features in a standard package to provide users with the industry's best innovation cost ratio.

LED1642GW Product Brief

LED1642GW is a low-voltage, low-power 16-bit monolithic shift register designed by STMicroelectronics for LED panels and display panels.

The LED1642GW guarantees a 20V output voltage and can drive multiple LEDs in series. There are sixteen regulated power supplies at the output, which provide a 3mA-36mA constant current output to drive the LED. The user can set the current through an external resistor, adjust the current in two sub-ranges with two 7-bit current gain registers, and adjust the brightness of each channel with a 12/16-bit gray scale controller.

The switching time can be set to four different values to help reduce system noise.

The LED1642GW provides an open/short fault detection mode, and the auto-shutdown and auto-on functions (optional) save power without any external intervention. The thermal management function alarms when overheating and shuts down the drive when the output is overheated (170 °C).

The high frequency clock of the serial interface (up to 30 MHz) makes this product suitable for high rate data transmission. An optional gradual output delay is used to reduce the inrush current, especially in a daisy-chain configuration where the optional SDO synchronization feature is useful. The power supply voltage ranges from 3V to 5.5V.

LED1642GW characteristics

Multiple functions of the LED 1642GW can be enabled through the configuration registers. Each feature is briefly described below.

Gain control and current range

The output current of the driver can be set by an external resistor connected between the R-EXT pin and the GND pin. At the same time, the current value can be modified by configuring the register-specific bits. Based on internal gain and range adjustment, the product can raise the current to 36mA or to 3mA. So you can change the output current without modifying the external resistor value to avoid modifying the hardware, as shown in Figure 2. This feature can also be used for global analog dimming, setting the driver output DC to adjust the brightness and color temperature of the LED.

Figure 2 – Internal Gain Adjustment

Error detection

Terminate the monitor to normal operation and turn on all channels of the drive to perform a fault check process to find LED lights or display failures. For example, you can find an open or shorted LED and determine where it is located, simplifying display inspection.

Automatic power off and wake up

This feature reduces power consumption when all output channels are off. This feature can be turned on or off by configuring the registers. When the latch data of all channels is "0" (output is off), the auto power off (AutoOFF) is started; when the first latch data string contains at least one data bit whose value is "1" (at least one output is Turned on), the drive will be reactivated (wake up). This feature significantly reduces the power consumption of the display, which is especially noticeable in large-screen display applications.

Switch time can be set

To further enhance design flexibility, the current generator can set the switching time (output current waveform). According to the actual application requirements, the switch time can be set to four different values by using the configuration register: 30/20ns, 100/40ns, 140/80ns, 180/150ns. The optional values are tON (upstream time) and tOFF (downflow time). This feature optimizes EMI performance during LED PWM operation.

SDO delay

Under normal conditions, the SDO pin data is shifted out on the rising edge of the clock signal. (In the figure below, the signal (1) propagation delay is approximately 15 ns). The SDO pin data is shifted out on the falling edge of the clock signal (in the figure below, the signal (2) propagation delay is approximately a few nanoseconds). This feature is enabled by properly setting the configuration registers, which is especially useful in daisy-chain configurations where data channel and clock channel delays are missing (board traces). SDO latency is a quick solution when the physical layer clock and data are difficult to synchronize. As shown in Figure 3.

Figure 3 – SDO Synchronization

Figure 4 – Gradual output delay

Gradual output delay

The essence of the gradual output delay is to gradually turn on the current generator to prevent all output channels from being turned on at the same time. In other words, when the PWM controller turns on the driver channel, the output channels can be started simultaneously or staggered. By setting the configuration register, the user can set the turn-on delay between the two output channels (10ns delay between two adjacent channels, and a delay of approximately 150ns between the first channel and the last channel). Figure 4 shows a typical output timing.

This feature prevents a large amount of inrush current from impacting the driver, reducing the value of the bypass capacitor and helping to reduce EMI interference.

PWM counter setting and brightness register

The brightness of each channel can be adjusted by controlling the 12/16-bit PWM grayscale brightness. Luminance data is loaded into the 16-bit shift register via the SDI pin, and each output channel has a shift register. The output PWM signal is generated by comparing the brightness register contents with a 16-bit or 12-bit counter (configuration register selection). The counter clock source is provided by the PWCLK pin as shown in Figure 5.

Figure 5 – PWM Signal Generation

By using a separate PWM control (local dimming), the LED brightness of each drive output can be changed (equivalent to current sharing regulation) while the color temperature remains the same because the operating point is related to the actual current.

Temperature mark

The product has a temperature control logic function that provides a flag status when the internal temperature is above 150 °C. If the temperature continues to rise above 170 °C, the thermal shutdown function will be activated, turning off the power analog terminal to protect the drive. However, the digital interface will continue to work to ensure daisy chain and data communication are working. Temperature control status information can be read via the SDO pin.

LED1642GW evaluation board

The STEVAL-ILL061V1 (Figure 6) is an application demonstration board for the LED1642GW driver. It is a high-brightness RGB LED array system board with local dimming and diagnostics based on the STM32 microcontroller and SPI interface. The ST L7981 DC/DC converter supplies power to the entire board. The demo board implements three LED drivers and an LED color temperature regulator that provides multiple lighting functions and graphics effects such as overall brightness variation, random color speed, color wave, configurable animation, and error detection.

Figure 6 – STEVAL-ILL061V1 Evaluation Board

The computer GUI graphical user interface software (Figures 7 and 8) allows the user to control all functions and set the pattern.

Figure 7 – LED1642GW PC GUI (Advanced Mode)

Figure 8 – LED1642GW PC GUI (Pattern Settings)

in conclusion

LED1642GW is ST's latest design flexible LED array driver with LED intelligent drive function, advanced LED fault detection and energy saving management functions, suitable for various applications. A full suite of evaluation kits (hardware boards and software development tools) allows users to easily and quickly develop enhanced LED driver solutions.