3/98

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

Latchable Negative Floating Hot Swap Power Manager

BLOCK DIAGRAM

UCC1921

UCC2921

UCC3921

UDG-99052

DESCRIPTION

The UCC3921 family of negative floating hot swap power managers pro-

vides complete power management, hot swap, and fault handling capa-

bility. 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 cur-

rent during a fault. All control and housekeeping functions are integrated

and externally programmable. These include the fault current level, maxi-

mum 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 de-

pends 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

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