Design of RGB LED color light drive control scheme based on power management chip

LED is a display device with excellent performance, with the advantages of long life, power saving, high brightness, multiple luminous colors, fast response speed and low driving voltage. While saving energy, it can also adjust the LED luminous intensity through PWM devices, adjust a variety of colors based on the principle of RGB three primary colors, and then realize a variety of display effects through MCU intelligent control. It is now widely used in urban lighting, architectural landscape lighting, stage lighting design and other fields.

This design adopts NXP Semiconductors (NXP) power management chips, microcontrollers, I2C devices, and LED driver devices to provide a complete set of solution designs for LED lighting system design.

Main chips: PCA9633/34/35: NXP I2 bus RGB/RGBA LED flashing/mixed light chip; TEA152x: NXP power chip; LPC92x: NXP 900 series MCU; P82B96/PCA9600: NXP I2C bus driver chip.

Main applications:

1. Point light source: Apply the principle of LED color screen display, enlarge its pixels, reduce the overall cost, each module is a color pixel. Application environment: bars, KTV, stages, shopping malls, exhibition halls, as music melody display, background wall decoration, curtain wall advertising, etc.

2. LED rainbow tube: Each tube consists of multiple color pixels (RGB), and each monochrome pixel can produce 256 grayscale changes. Application environment: decorative lighting in different places such as overpasses, river guardrails, and building exterior walls.

System hardware design:

The LED colored light control system mainly consists of three parts: drive module, control module and LED power supply.

1. Driver module design

How to make the LED module present different colors mainly relies on the principle of intermittent inertia of human vision, and uses the duty cycle of the three primary colors of R, G, and B to achieve color mixing. The LED color display of this design mainly relies on NXP's I2C interface LED flashing/mixed light driver chip PCA9633 (PCA9633-4-bit PWM output, PCA9634-8-bit PWM output, PCA9635-16-bit PWM output) to output 256 grayscale colors to achieve color display. The controller only needs to transmit the grayscale value of the RGB color of the module to achieve color display.

PCA9633 is a four-bit LED driver with programmable PWM output controlled by I2C bus. It is mainly used for LEDRGB/RGBA (Red/Green/Blue/Amber) mixed light. The main performance indicators are as follows:

1. 4-channel LED driver, each driver can be programmed into four states through software, namely: on, off, programmable PWM flashing control output, programmable gray level for each channel, and supports PWM mixed light output with four-channel overall brightness adjustment.

2. Dimming control, PWM output frequency 97kHz, each channel has 256 gray levels.

3. Flicker control, PWM programmable frequency range 24Hz~10.73s, duty cycle programmable range 0%~99.6%.

4. The overall brightness of the four-way PWM output can be adjusted in 256 levels through 190Hz PWM output.

5. The four-bit output can be programmed to push-pull output (at 5V, sink current 25mA, source current 10mA).

6. 7 hardware address setting pins, the same I2C bus can connect up to 126 chips.

7. Each PCA9633 has four programmable software addresses: one global response address and three sub-addresses.

8. Built-in 25MHz crystal oscillator and power-on reset circuit, can also achieve software reset through I2C bus.

9. SDA/SCL has built-in noise filter and supports 1MHz I2C fast mode.

10. Support hot plug-in, low standby current, support voltage range: 2.3~5.5V.

The following figure shows the design of the driver unit, where the number of red, green and blue LEDs can be multiple. You can choose parallel or series connection according to your design requirements, and then choose a suitable switch tube according to the LED connection method and voltage/current requirements. A small number of LEDs can also be directly driven by PCA9633. For specific parameters, see PCA9633 data. The driver module sets the access address through the A6~A0 pins of PCA9633, and it can work normally when connected to the I2C bus output by the control module. Each I2C bus can connect 126 dimming driver modules.

2. Control module design

The control module is shown in the figure below. Its main function is to control all dimming modules on the I2C bus through the MCU to achieve various display effects. P82B96 is an I2C bus driver chip used to improve the bus driving capability. When the transmission rate is 20~50kbps, the transmission distance can reach 1km. The MCU can be selected according to the actual system requirements. While controlling the dimming of the bus devices, other operations can also be added, such as display image processing, communication with PC, and expansion of storage space, etc.

The connection between the control module and the drive module is shown in the figure below.

The comparison of I2C bus transmission rate and cable length with other buses is shown in the figure below.

3. Power supply

The specific parameters of the power supply should be determined according to factors such as the specific number of LEDs and the connection method. The figure below shows an LED power supply solution using the NXP STARplug series chip. This solution has the advantages of simple design, small size, wide voltage input, low cost, low loss, etc., and is widely used in the LED field.