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
` 250s Glitch Filter on the SDFLTCH pin
` 8-Pin DIL and SOICPinout
SpecificationsIVDD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA
SDFLTCH Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10mA
PL Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10mA
IMAX Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VDD
Storage Temperature . . . . . . . . . . . . . . . .. . -65°C to +150°C
Junction Temperature. . . . . . . . . . . . . . . . . 55°C to +150°C
Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . +300°C
All voltages are with respect to VSS (the most negative voltage).
Currents are positive into, negative out of the specified terminal.
Consult Packaging Section of Databook for thermal limitations and considerations of packages.DescriptionThe UCC3921 family of negative floating hot swap power managers provides omplete power management, hot swap, and fault handling capability.The IC is referenced to the negative input voltage and is poweredthrough an external resistor connected to ground, which is essentially acurrent drive as opposed to the traditional voltage drive. The onboard10V shunt regulator protects the IC from excess voltage and serves as areference for programming the maximum allowable output sourcing currentduring a fault. All control and housekeeping functions are integratedand externally programmable. These include the fault current level, maximumoutput sourcing current, maximum fault time, selection of Retry or atched mode, soft start time, and average power limiting. In the event ofa constant fault, the internal timer will limit the on time from less than .1% to a maximum of 3% duty cycle. The duty cycle modulation depends n the current into PL, which is a function of the voltage across he FET, thus limiting average power dissipation in the FET. The fault evel is fixed at 50mV across the current sense amplifier to minimize total dropout. The fault current level is set with an external urrent sense resistor, while the maximum allowable ourcing current is programmed with a voltage divider rom VDD to generate a fixed voltage on IMAX. The current evel, when the output acts as a current source, is qual to VIMAX/RSENSE. If desired, a controlled current tart up can be programmed with a capacitor on IMAX.
When the output current is below the fault level, the output evice is switched on. When the output current exceeds he fault level, but is less than the maximum ourcing level programmed by IMAX, the output remains witched on, and the fault timer starts charging CT. Once T charges to 2.5V, the output device is turned off and erforms a retry some time later (provided that the selected ode of operation is Automatic Retry Mode).When the output current reaches the maximum sourcing urrent level, the output acts as a current source, limiting he output current to the set value defined by IMAX.
Other features of the UCC3921 include undervoltage ockout, 8-pin Small Outline (SOIC) and Dual-In-Line DIL) packages, and a Latched Operation Mode option,in which the output is latched off once CT charges to .5V and stays off until either SDFLTCH is toggled (for reater than 1ms) or the IC is powered down and then ack up.
UCC3921 Data Sheet
