Microchip — ARD00922 Tunable White LED Driver Reference Design

Microchip has developed a market-ready integrated solution which implements tunable white lighting operated via a Bluetooth^® wireless link to a control app on a smartphone.

The ARD00922 reference design combines an HV9961 buck LED driver with an 8-bit PIC16F15313 microcontroller. The MCU communicates with an RN4871 Bluetooth Low Energy radio module via a UART interface to link to any smartphone running the ARD00922 app. The app enables the user to control both the brightness and the color temperature of the output from twin parallel warm- and cool-white strings each of 10 LEDs, which have a correlated color temperature of 2,700 K and 6,500 K.

The HV9961 is an average current-mode control LED driver IC operating in constant off-time mode. This control IC does not produce a peak-to-average error, and therefore greatly improves accuracy, line, and load regulation of the LED current without any need for loop compensation or high-side current sensing. The accuracy of the LED output current is ±3%.

The RN4871 integrates a Bluetooth 4.2 baseband controller, an on-board Bluetooth protocol stack, digital and analog I/O, and an RF power amplifier into a single module.

The RN4871 uses a private transparent UART wireless service which simplifies the transfer of serial data over Bluetooth Low Energy devices. In the application, the RN4871’s transparent UART provides an end-to-end data pipe between the PIC16F15313 microcontroller and a smartphone.

The microcontroller and the Bluetooth module both operate directly from a grid power supply at 120 V or 230 V ac. Power regulation to these components is effected by means of a bridge rectifier and a DN2470 depletion FET. This is followed by the MCP1703, a 3.3 V low-dropout regulator (LDO).