SLVUAW9C September 2016 – February 2020 UCD90320
For parameters not directly related to output voltage, the UCD90320 supports the linear data format described in section 7.1 of the PMBus specification. This linear format is a two-byte value that contains an 11-bit, twos-complement mantissa and a 5-bit, twos-complement exponent.
The relationship between the PMBus parameter and the real-world value is given by the formula:
Where:
R is the real-world value,
Y is an 11-bit, signed twos-complement binary integer mantissa, and
X is the signed 5-bit, `twos-complement binary integer exponent.
This pseudo floating-point notation allows values as large as ≈33E6 down to ≈15E-6 to be sent over the PMBus. The internal variables used by the UCD90320 firmware are mostly 16 bits wide and do not support such a wide range of values. The resolution of a PMBus setting depends strongly on both the exponent of the PMBus value (larger values have coarser resolution) and the scaling of the internal variables.