Blinking across multiple PCA9745B LED drivers

oliverebert — Tue, 16 Jan 2018 11:29:01 GMT

Hello,

we're using two (SPI-)daisy-chained NXP PCA9745B LED drivers and want to blink some LEDs synchronously on both ICs. The respective LEDs of each driver are associated with a LED group that is configured identically on both ICs. The gradation start command is issued simultaneously to both ICs. While the LEDs on each IC are blinking in sync (as expected), the blinking frequencies between different ICs seem to differ and the blinking LEDs diverge pretty quickly! I don't see any facilities for synchronizing multiple drivers (except for using the /OE pin for external dimming/blinking?)... am I missing something? Is this use case even supported by the drivers?

How would one go about blinking LEDs synchronously across multiple PCA9745B LED drivers?

Thanks and regards

Oliver

Re: Blinking across multiple PCA9745B LED drivers

oliverebert — Wed, 17 Jan 2018 15:07:04 GMT

An FAE from our distributor confirmed that it is indeed not possible to synchronize two or more PCA9745Bs to achieve e.g. synchronous gradation operation as described above. This is due to the spread of the 8 MHz internal oscillator frequencies across different ICs (presumably 20--30%?), and an input for an external clock is not available. Anyway, this seems like a missed opportunity ...

topic Re: Blinking across multiple PCA9745B LED drivers in 8-bit Microcontrollers

Blinking across multiple PCA9745B LED drivers

Re: Blinking across multiple PCA9745B LED drivers