Oscillations on VDDA/CY8C5868AXI | Cypress Semiconductor
Oscillations on VDDA/CY8C5868AXI
I have a small oscillation on signal VDDA of PSOC chip CY8C5868AXI (see attached oscilloscope image, Fig_1).
After some work, I have realized that if I disconnect this signal from the chip it dissapears. Please find attached also the power schematic of the CY8C5868 (Fig_2) and the the power generation of my board (Fig_3) As you can see, there are basically two 5 volts power signal: VCC for digital stuff and +5V_A for analog stuff.
In Fig.3, 5V_IN is generated in a external power supply, then get into the board through CN1, after a ferrite bead filter, becomes VCC.
As I wanted to have a clear analog power supply, +5V_A is generated using U20 and U21, see also Fig.3.
I have measured with a multimeter VCC and +5V_A and get: VCC= 5.049V and +5V_A= 5.025.
On datasheet for this chip, pag 12/139, says "VDDA must be the highest voltage present on the device. All other supply pins must be less than or equal to VDDA." In my board, as I have described above, this is not true. Do you think that small difference of voltages between VCC and +5V_A is the cause of this oscillation?
Thanks in advance,