UCC1917

The UCC3917 family of positive floating hot swap managers provides complete power management, hot swap, and fault handling capability. The voltage limitation of the application is only restricted by the external component voltage limitations. The IC UCC3917 provides its own supply voltage via a charge pump off of VOUT. The onboard 10V shunt regulator protects the IC from excess voltage. The IC UCC3917 also has catastrophic fault indication to alert the user that the ability to shut off the output NMOS has been bypassed. 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 NMOS power limiting.

The UCC3917 fault level across the current sense amplifier is fixed at 50mV to minimize total drop out. Once 50mV is exceeded across the current sense resistor, the fault timer will start. The maximum allowable sourcing current is programmed with a voltage divider from the VREF/CATFLT pin to generate a fixed voltage on the MAXI pin. The current level at which the output appears as a current source is equal to VMAXI divided by the current sense resistor. If desired, a controlled current startup can be programmed with a capacitor on MAXI.

When the UCC3917 output current is below the fault level, the output device is switched on with full gate drive. When the output current exceeds the fault level, but is less than maximum allowable sourcing level programmed by MAXI, 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 attempts either a retry sometime later or waits for the state on the LATCH pin to change if in latch mode. When the output current reaches the maximum sourcing current level, the output device appears as a current source.