Power rail spikes from ILI9341 driver

[Klemken]

Hello,

i designed a complex motherboard for my project and an LCD whit ILI9341 on seperate pcb, whit FFC 50 pin connection in beetwen PCBs. On motherboard i have a cortex m0 MCU, XTR115 for current loop driver, ATB1000 Bluetooth module, opamps, eeprom, 3.3V output DC/DC converter and a ton of other stuff. On the LCD pcb i only have the 2.8TFT LCD whit ILI9341v driver and few AT42QT10 chips for 4 touch buttons. Everything is working perfectly, only thing is that there are periodicals (412kHz) voltage spikes and dips on my +3.3V power rail (from 3.1 to 3.4V). These spikes are not causing any problems, but since this product will go into semi-mass porduction later this year, i want it to be as good as can be. By removing or turning off separate components i found the cause of them to be ILI9341 logics and the LEDs backlight. The backlight produces around 70% of the spikes amplitude, the rest is from ILI9341 logics. What would be best solutions? I already have several ceramic 1206 capacitors right next to LCDs connector, but looks like i need to add more filters. Was thinking of adding a ferrite bead whit a capacitor next to eat to block and remove spikes into gnd?

Thank in advance.