78M6610+LMU Data Sheet
High Pass Filters and Offset Removal
Offset registers for each analog input contain values to be subtracted from the raw ADC outputs for the
purpose of removing inherent system DC offsets from any calculated power and RMS values. These
registers are signed fixed point numbers with a possible range of -1.0 to 1 - LSB. They default to 0 and
can be manually changed by the user or integrated offset calibration routines.
Register
S1_OFFS
S0_OFFS
S3_OFFS
S2_OFFS
Description
Current Input S1 Offset Calibration
Voltage Input S0 Offset Calibration
Current Input S3 Offset Calibration
Voltage Input S2 Offset Calibration
Alternatively, the user can enable an integrated High Pass Filter (HPF) to dynamically update the offset
registers every accumulation interval. During each accumulation interval (or low-rate cycle) the HPF
calculates the median or DC average of each input. Adjustable coefficients determine what portion of the
measured offset is combined with the previous offset value.
HPF_COEF_x registers contain signed fixed point numbers with a usable range of 0 to 1 - LSB (0.99999),
negative values are not supported. By default, they are initialized to 0.5 (0x400000) meaning the new
offset value will come from one-half of the measured offset and one-half will come from the previous
offset value. Setting them to 1.0 (0x7FFFFF) causes the entire measured offset to be applied to the offset
register enabling lump-sum offset removal. Setting them to zero disables any dynamic update of the
offset registers by the HPF.
Register
Description
HPF_COEF_I
HPF_COEF_V
HPF coefficient for S1 and S3 current inputs
HPF coefficient for S0 and S2 voltage inputs
To allow the DC component of the load current to be included in the measurement (i.e. half-wave rectified
current waveforms), the HPF_COEF_I coefficients must be set to zero.
Using the offset calibration routine will automatically set the filter coefficients to zero to disable the HPF.
17
Rev 0
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
