Difference between core power pad and IO pad

[RuihW]

Hello everyone,

I'm designing the IO ring with TSMC 0.18um PDK. In my design, the majority of the FETs are 1.8V. But there are some 3V FETs that need 3V for gate (they still use 1.8V for Vds). The 0.18um PDK has two pads: PVDD3A and PVDD3AC. Which one should I use for VDD? My understanding is that since the core is based on 1.8V, I should use 3AC. Am I correct?

 

[rafauy]

What does the documentation say about the A and AC variants? Whats the difference between them?

 

[RuihW]

What does the documentation say about the A and AC variants? Whats the difference between them?

The "C" stands for core. According to the databook, the A variant is for IO voltage (3.3V) and AC is for core voltage (1.8V). After reading the documents, I think I'll use the AC variant for VDD/VSS, and place power-cut cells to isolate the 3V pins.