The UCC3912 family of hot swap power managers provides complete power management, hot swap capability, and circuit breaker functions. The only component required to operate the device, other than supply bypassing, is the fault timing capacitor, CT. All control and housekeeping functions are integrated, and externally programmable. These include the fault current level, maximum output-sourcing current, maximum fault time, and startup delay. In the event of a constant fault, the internal fixed 3% duty cycle ratio limits average output power.
The internal 4-bit DAC allows programming of the fault level current from 0 A to 3 A with 0.25-A resolution. The IMAX control pin sets the maximum sourcing current to 1 A above the fault level when driven low, and to a full 4 A when driven high for applications which require fast output capacitor charging.
When the output current is below the fault level, the output MOSFET is switched on with a nominal on resistance of 0.15 . When the output current exceeds the fault level, but is less than the maximum sourcing level, the output remains switched on, but the fault timer starts charging CT. Once CT charges to a preset threshold, the switch is turned off, and remains off for 30 times the programmed fault time. When the output current reaches the maximum sourcing level, the MOSFET transitions from a switch to a constant current source.
The UCC3912 family is designed for unidirectional current flow, emulating an ideal diode in series with the power switch. This feature is particularly attractive in applications where many devices are powering a common bus, such as with SCSI Termpwr.
The UCC3912 family can be put into sleep mode drawing only 1-µA of supply current. The SHTDWN\ pin has a preset threshold hysteresis which allows the user the ability to set a time delay upon startup to achieve sequencing of power. Other features include an open drain FAULT\ output indicator, thermal shutdown, under voltage lockout, and a low thermal resistance small outline package.
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