UCC3921 Datasheet | Unitrode

FEATURES - Precision Fault Threshold - Programmable: Average Power Limiting, Linear Current Control, Overcurrent Limit and Fault Time - Fault Output Indication Signal - Automatic Retry Mode or Latched Operation Mode - Shutdown Control - Undervoltage Lockout - 250µs Glitch Filter on the SDFLTCH pin - 8-Pin DIL and SOIC DESCRIPTION The UCC3921 family of negative floating hot swap power managers provides plete power management, hot swap, and fault handling capability. The IC is referenced to the negative input voltage and is powered through an external resistor connected to ground, which is essentially a current drive as opposed to the traditional voltage drive. The onboard 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, selection of Retry or Latched mode, 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% duty cycle. The duty cycle modulation depends on the current into PL, which is a function of the voltage across the FET, thus limiting average power dissipation in the FET. The fault level is fixed at 50m V across the current sense amplifier to minimize total (continued) BLOCK DIAGRAM 3/98 UDG-99052 DESCRIPTION (continued) dropout. The fault current level is set with an external current sense resistor, while the maximum allowable sourcing current is programmed with a voltage divider from VDD to generate a fixed voltage on IMAX. The current level, when the output acts as a current source, is equal to VIMAX/RSENSE. If desired, a controlled current start up can be programmed with a capacitor on IMAX. When the output current is below the fault level, the output device is...