Sort of a general question/warning. On the caravel/caravan framework, there are two 3.3V sources, vdda1 and vdda2. Circuits using these voltages should be using
sky130_fd_sc_hvl
, correct? All the other standard cell libraries only have 1.8v rated mosfets.
a
Arman Avetisyan
02/09/2022, 7:31 PM
yes
t
Tim Edwards
02/09/2022, 9:19 PM
@User: These sources can be run at 1.8V, so it depends on the intent of the designer. The normal setup, and the general intent, is to have all
vdda
supplies at 3.3V and
vccd
supplies at 1.8V. But all of the user domains are independent, and unconnected on the development board except through jumpers. I don't know how well the high voltage clamps work at 1.8V, but the I/O cells are rated for VCCIO down to 1.8V, so I suppose they must still provide sufficient ESD protection at 1.8V.
m
Mitch Bailey
02/09/2022, 11:56 PM
Thanks for the feedback. So I guess if you're using 3.3V, be sure to use
sky130fd_sc_hvl
, but if vdda1 and vdda2 are 1.8V, you're free to use any library.
t
Tim Edwards
02/10/2022, 1:23 PM
Right. But unless the designer really needed three or four independent digital supplies, then they would presumably use
vccd1
and
vccd2
, so I would think that the use of 1.8V devices on any
vdda*
supply should be flagged with a warning. Obviously mixed high- and low-voltage libraries on the same supply would be flagged as an outright error.
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