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It is well known that short circuits or severe overcurrents are critical problems. Designing with programmable current limiting allows management and protection of the power source or receiving device while following the USB standard or system level guidelines that are needed for safety and reliability. In this application, a single resistor RSET is used to control the current. For clarity there will be range of currents for a given resistor to account for the variation in each of the supporting circuits. As opposed to a sense resistor in series with PMOS, current limiting is based on a current mirror circuit that creates a sense current that is a proportional replica of IOUT. The sense current available at the ISET node is used to develop a voltage across the external resistor RSET. This voltage now denoted as VFB is used in conjunction with a reference voltage to send the appropriate current limiting signal to the Gate Driver block. Current Limiting Foldback is invoked when VOUT is less than 1V during severe loads or short circuits. The current will now be less than the programmed current reducing power dissipation as a second level of protection. If the foldback protection is inadequate, Thermal Shutdown will be invoked.
