SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
The Xn value is used directly as an input to the Proportional (P) branch of the filter. It is multiplied by the 16 bit signed Kp coefficient, and the 24 bit result is used as the output of the P branch. When multiplying two signed numbers in binary arithmetic, an extra sign bit is generated. Because of this, 9 bits times 16 bits gives 24 meaningful bits, not 25.
No clamp is needed on the proportional branch. It is self-limiting, because it has no memory. It will never exceed 24 bits. If a lower maximum output is desired from the proportional branch, it can be achieved by reducing the value of Kp.