Smart Grid Solutions Guide - Maxim

Power-grid monitoringOverviewAdditionally, electronic calibrationallows for periodic self-test and calibrationto compensate for environmentalfactors (e.g., temperature,humidity, and drift) in the field.CDACs and CDPots allow both thetop and bottom DAC voltage tobe set to arbitrary voltages, thusremoving excess adjustment range.In the calibration diagram below,a low value of 1V and a high valueof 2V are selected. To achieve a0.0039V step size over the 1V to 2Vrange, only an 8-bit device is needed.This approach reduces cost andincreases accuracy and reliability byremoving any possibility that thecircuit could be grossly misadjusted.The high and low voltages for theCDAC are arbitrary and, therefore,can be centered wherever circuitcalibration is required. Thus, thegranularity of the adjustmentcan be optimized for the specificapplication. In addition, CDACs andCDPots have internal nonvolatile(NV) memory, which automaticallyrestores the calibration settingduring power-up.Precision voltage referencesSensor and voltage measurementswith precision ADCs are only asgood as the voltage reference usedfor comparison. Likewise, outputcontrol signals are only as accurateas the reference voltage supplied tothe DAC, amplifier, or cable driver.Common power supplies are notadequate to act as precision voltagereferences. They are not accurateenough and drift far too much withtemperature.Compact, low-power, low-noise, andlow-temperature-coefficient voltagereferences are affordable and easyto use. In addition, some referenceshave internal temperature sensors toaid in the tracking of environmentalvariations.ORDINARY DAC4VREFIN4V10-BITDACOUT10 BITS, 1024 STEPSGroundFB0.0039Vper stepGROUNDCALIBRATION DAC2V2VREFHI8-BITDAC8 BITS, 256 STEPS1VREFLOOUT1VComparing the calibration range of an ordinary DAC to a CDAC.www.maxim-ic.com/smartgrid 15