A level down shifter circuit includes a latch and an assist circuit. The latch is configured to generate a digital shifted signal and a complementary shifted signal by a voltage downshift of a digital input signal and a complementary input signal. The digital input signal and the complementary input signal are in a first voltage domain. The digital shifted signal and the complementary shifted signal are in a second voltage domain. The second voltage domain has a smaller voltage range than the first voltage domain. The assist circuit is configured to alternately pull the digital shifted signal and the complementary shifted signal to an intermediate voltage in response to the digital input signal and the complementary input signal. The intermediate voltage is in the second voltage domain.