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SLUS384B – NOVEMBER 1999 – REVISED JUNE 2000
DP PACKAGE
(TOP VIEW)
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Integrated 0.075-Ω Power MOSFET
3 V to 6 V Operation
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3
4
5
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7
8
16
15
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13
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9
External Analog Control of Fault Current
from 0 A to 4 A
VIN
VIN
VIN
GND*
GND*
VOUT
VOUT
VOUT
GND*
GND*
NC
Independent Analog Control of Current
Limit Up to 5 A
Fast Overload Protection
Unidirectional Switch
FAULT
SHTDWN
IFAULT
CT
IMAX
Minimal External Components
1-µA I
When Disabled
Pin 5 serves as the lowest impedance to the electrical
ground. Pins 4, 12, and 13, serve as heat sink/ground.
These pins should be connected to large etch PCB areas
to help dissipate heat.
CC
Programmable On Time
Programmable Start Delay
Fixed 3% Duty Cycle
description
The UCC3918 low on-resistance hot swap power manager provides complete power management, hot swap
capability, and circuit breaker functions. The only components needed to operate the device, other than supply
bypassing, are a timing capacitor, and two programming resistors. 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 the average output power. The IFAULT pin allows linear programming of the fault level current from
0 A to 4 A.
Fast overload protection is accomplished by an additional overload comparator. Its threshold is internally set
above the maximum sourcing current limit setting. In the event of a short circuit or extreme current condition,
this comparator is tripped, shutting down the output. This function is needed since the maximum sourcing
current limit loop has a finite bandwidth.
When the output current is below the fault level, the output MOSFET is switched on with a nominal resistance
of 0.075 Ω. When the output current exceeds the fault level or the maximum sourcing level, the output remains
on, but the fault timer starts charging a capacitor connected to the CT pin (C ). Once C charges to a preset
T
T
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 UCC3918 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 termintation power (Termpwr). The UCC3918 can also be put into the sleep mode, drawing
only 1 µA of supply current.
Other features include an open-drain fault output indicator, thermal shutdown, undervoltage lockout, 3 V to 6 V
operation, and a low thermal resistance small-outline power package.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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Copyright 2000, Texas Instruments Incorporated
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