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
· 250ms Glitch Filter on the SDFLTCH
pin
· 8-Pin DIL and SOIC

DESCRIPTION
The UCC3921 family of negative floating hot swap power managers provides
complete 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 50mV across the current sense amplifier to minimize total
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 switched on. When the output current exceeds
the fault level, but is less than the maximum
sourcing level programmed by IMAX, 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 (provided that the selected
mode of operation is Automatic Retry Mode).
When the output current reaches the maximum sourcing
current level, the output acts as a current source, limiting
the output current to the set value defined by IMAX.
Other features of the UCC3921 include undervoltage
lockout, 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
2.5V and stays off until either SDFLTCH is toggled (for
greater than 1ms) or the IC is powered down and then
back up.