Convert camelCase to snake_case ignoring multiple uppercase

I would like to convert camelCase to snake_case, but ignoring multiple capitalized letters in the camelCase.
I have the following function:

re.sub(r'(?<!^)(?=[A-Z])', '_', name).upper()

This returns the following results:

abcFunction --> ABC_FUNCTION
ABCFunction --> A_B_C_FUNCTION

Is there a way to get the following:

abcFunction --> ABC_FUNCTION
ABCFunction --> ABC_FUNCTION

>Solution :

import re

name = 'abcFunction'
name2 = 'ABCFunction'
def converter(name):
    name = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', name)
    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', name).upper()

print(converter(name))
print(converter(name2))

Output

ABC_FUNCTION
ABC_FUNCTION