Engineers who design circuits for automotive equipment, industrial devices, test-and-measurement instruments, and solar-power inverters often must measure supply currents and in most cases, they pass a current through a small-value resistance and measure the voltage drop across it. You can find application notes such as “Current Sense Circuit Collection,” App. Note 105 from Linear Technology and “High-Side Current-Sense Measurement: Circuits and Principles,” App. Note 746, from Maxim Integrated Products. The common circuits place a differential amplifier’s inputs across the resistance to provide a measurable voltage at the amplifier’s output.
STmicroelectronics now gives designers a variation on the high-side current-measurement theme. The TSC102 integrated circuit can operate with current flows at up to 30V and it can applied voltages from -16V to 60V. A voltage in this range can result from switching transients or reversed battery connections.
But in a more interesting vein, the TSC102 includes an extra operational amplifier that gives engineers uncommitted input and output connections. So what’s the big deal? Well, having a “spare” op amp lets equipment designers adjust the amplitude of the current measurement, set up a comparator as an over- or under-voltage detector, of create a first- or second-order low-pass filter to help stabilize the voltage output and reduce interference from noise.
The 24-page data sheet for the TSC102 “high-side current sense amplifier plus signal conditioning amplifier,” includes six schematic diagrams that suggest ways to use the extra op amp. To obtain the data sheet, go to: www.st.com/stonline/products/literature/ds/16754.pdf.
Some might ask, “Why measure the high-side current, wouldn’t measuring the current as it goes to ground work just as well?” I’ll leave it to you to offer an answer. –Jon Titus
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