Digital and Analog Power Connection??

[davyzhu]

Hello all,

I use a 1.8v core power supply to the main CPU, and the CPU has internal analog PLL need 1.8v analog power supply. I found the reference use two paralleled 10 Ohm resisters to form a 5 Ohm resister between the two power supply. But why to use the small resister?

I found the traditional usage is to connect the two supply with a wire (or 0Ohm resister) and a Ferrit Bead, which one is better?

Regards,

Davy Zhu

 

[nicleo]

My guess:
The resistors prevent the (noisy) current (in EMC point of view, it's a closed loop) from the VCC_1.8_CPU_CORE to flow through the GND_S_CPU_PLL. Current prefers lower impedance path. Pls correct if I'm wrong.