To format Fat16 on the Mac you will need to use the Terminal app.
Insert the card and from the command line type this:
diskutil list
Locate the “Identifier” for the card. In my case, it was “disk7”.
To format the card, it needs to be unmounted using “diskutil”. Here is the command:
diskutil unmountDisk disk7
You will get a message telling you if that was successful. If it is, here is the command to format the card Fat16 with the name “DSD”:
sudo newfs_msdos -F 16 -v DSD /dev/disk7
You will be asked to enter your superuser password. That is normally the password of the main account setup as an admin account.
I tested this with a 16GB card and it was formatted to a capacity of 2.15GB.