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Combined current sense for high- and low-side power transistors Disclosure Number: IPCOM000018993D
Original Publication Date: 2003-Sep-25
Included in the Prior Art Database: 2003-Sep-25

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Up to now two separated gain stages are used simultaneously for current sensing, one with a high-side the other with a low-side power transistor. The drawback of this technology is the essential well matching of the both gain stages. It requires an expensive and complex trimming of this two stages. Also the offsets of the gain stages are usually not exactly identical what introduces output signal errors. This invention shows a method to unite the two gain stages in one circuit with a half bridge architecture. The core of the invention is a simple operational transconductance (OTA) amplifier which is used for a synchronous DC-to-DC converter (figure 1). The current IL is the sum of IHS (current at high-side power transistor) and ILS (current at low-side power transistor). If no current is flowing through the power transistors the voltages Va and Vb are respective: