78M6610LMU Datasheet, PDF (27/63 Pages) Maxim Integrated Products – Energy Measurement Processor for Load Monitoring Units

78M6610+LMU Data Sheet
Calibration
The 78M6610+LMU provides integrated calibration routines to modify gain and offset coefficients. The
user can set up and initiate a calibration routine through the Command Register. When in calibration
mode, the line-lock bit should be set for best results.
The calibration routines will write the new coefficients to the relevant registers. The user can then save
the new coefficients into flash memory as defaults using the flash access command in the Command
Register.
See the Command Register section for more information on using commands.
Voltage and Current Gain Calibration
In order to calibrate the gain parameters for voltage and current channels, a reference AC signal must be
applied to the channel to be calibrated. The RMS value corresponding to the applied reference signal
must be entered in the relevant target register (VTARGET, ITARGET). Considering calibration is done
with low-rate RMS results, the value of the target register should never be set to a value above 70.7% of
full-scale.
Initially, the value of the gain is set to unity for the selected channels. RMS values are then calculated on
all inputs and averaged over the number of measurement cycles set by the CALCYCS register. The new
gain is calculated by dividing the appropriate Target register value by the averaged measured value. The
new gain is then written to the select Gain registers unless an error occurred.
On a successful calibration, the command bits are cleared in the Command Register, leaving only the
system setup bits. In case of a failed calibration, the bit in the Command Register corresponding to the
failed calibration is left set.
Offset Calibration
To calibrate offset, all signals should be removed from all analog inputs although it is possible to do the
calibration in the presence of AC signals. In the command, the user also specifies which channel(s) to
calibrate. Target registers are not used for Offset calibration.
During the calibration process, each input is accumulated over the entire calibration interval as specified
by the CALCYCS register. The result is divided by the total number of samples and written to the
appropriate offset register if selected in the calibration command. Using the Offset Calibration command
will set the respective HPF coefficients to zero thereby fixing the Sx_OFFS offset registers to their
calibrated values. Upon completion of calibration, only the 0xCAxxxx bits of the Command Register are
cleared.
Die Temperature Calibration
To re-calibrate the on-chip temperature sensor offset, the user must first write the known chip
temperature to the T_TARGET register. Next, the user initiates the Temperature Calibration Command in
the Command Register. This will update the T_OFFS offset parameter with a new offset based on the
known temperature supplied by the user. The T_GAIN gain register is set by the factory and not updated
with this routine. The range of the Die Temperature registers is -128 to +128 - LSB Degrees Celsius.
27
Rev 0