a recent article from electronic design, written by dan harmon, marketing manager of the current and power measurement product line at texas instruments (ti), describes techniques for minimizing the effects of temperature on current measurements in a system to improve system performance and lessen design margins.
the article gives techniques for minimizing the effects of temperature on current measurement. (wikimedia commons)
harmon wrote, “using current measurements for thermal management is a leading indicator of system performance and faults, whereas simply monitoring the temperature is potentially a lagging indicator. accurately monitoring the current consumed, especially over temperature, has become vital as designers pack more functionality into tighter areas.”
there are several causes listed by harmon that could lead to inaccurate current measurements including gain error and gain drift and power-supply rejection ration in the amplifier or pcb layout and shunt-resistor tolerance and drift at the system level.
drift was mentions in four of the seven total issues that harmon orginally listed, making it a primary focus for reducing errors.
the article explores discrete current measurement implementations, the importance of calibration, and using current-sense amplifiers, which harmon explains are designed to precisely match gain errors with temperature drift. he wrote, “the absolute accuracy of the resistors isn’t a factor in minimizing gain error; what’s critical is how well they’re matched. if both rf and ri are off by 10% in the same direction (either plus or minus), then the ratio remains ideal and the gain error is zero.”
the article concluded, “while room-temperature calibration is relatively straightforward, performing multi-temperature calibration is time-consuming and expensive. using a current-sense amplifier that integrates a precisely matched, resistive gain network will minimize the temperature-drift effects of the gain error.”
read the full article at http://www.electronicdesign.com/power/minimizing-temperature-drift-your-current-measurement.
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