How do I calculate the tolerance on the Vtt supply for DDR3?

Description

When calculating the tolerance for DDR3 Vtt supplies using SSTL15, it is with respect to VCCIO. But you should also take the VCCIO tolerance into the calculation.

Vtt(min) = VCCIO(min) * 0.49 Vtt(min) = 1.425V * 0.49 Vtt(min) = 0.70V

Vtt(typ) = VCCIO(typ) * 0.5 Vtt(typ) = 1.5V * 0.5 Vtt(typ) = 0.75V

Vtt(max) = VCCIO(max) * 0.51 Vtt(max) = 1.575V * 0.51 Vtt(max) = 0.80V

The actual tolerance across min and max conditions is /-50mV.

This same analysis can be performed for all SSTL and HSTL I/O standards.