UCC3913

The UCC1913 family of negative voltage circuit breakers provides complete power management, hot swap, and fault handling capability. The IC is referenced to the negative input voltage and is driven through an external resistor connected to ground, which is essentially a current drive as opposed to the traditional voltage drive. The on-board 10V shunt regulator protects the IC from excess voltage and serves as a reference for programming the maximum allowable output sourcing current during a fault. All control and housekeeping functions are integrated, and externally programmable. These include the fault current level, maximum output sourcing current, maximum fault time, soft start time, and average power limiting. In the event of a constant fault, the internal timer will limit the on-time from less than 0.1% to a maximum of 3%. The duty cycle modulates depending on the current into the PL pin, which is a function of the voltage across the FET, and will limit average power dissipation in the FET. The fault level is fixed at 50mV across the current sense amplifier to minimize total dropout. The fault current level is set with an external current sense resistor. The maximum allowable sourcing current is programmed with a voltage divider from VDD to generate a fixed voltage on the IMAX pin. The current level, when the output appears as a current source, is equal to _VIMAX/R_SENSE. If desired, a controlled current startup can be programmed with a capacitor on the IMAX pin.

When the output current is below the fault level, the output device is switched on. When the output current exceeds the fault level, but is less than the maximum sourcing level programmed by the IMAX pin, the output remains switched on, and the fault timer starts charging CT. Once CT charges to 2.5V, the output device is turned off and performs a retry some time later. When the output current reaches