UCC 29 18 /8 15 10
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SLUS457B – JULY 2000 - REVISED OCTOBER 2000
N and DP PACKAGES
(TOP VIEW)
D
Integrated 0.075-Ω Power MOSFET
D
D
3 V to 6 V Operation
External Analog Control of Fault Current
From 0 A to 4 A
VIN
VIN
VIN
VOUT
VOUT
VOUT
GND*
GND*
1
2
3
4
5
6
7
8
16
15
14
13
12
D
Independent Analog Control of Current
Limit up to 5 A
GND*
GND*
D
D
D
D
D
D
D
Fast Overload Protection
Unidirectional Switch
FAULT
11 NC
10 CT
SHTDWN
IFAULT
Minimal External Components
9
IMAX
1-µA I
When Disabled
CC
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. For N package, pins 4, 12, and 13,
are NC.
Programmable On Time
Programmable Start Delay
Fixed 3% Duty Cycle
description
PWP PACKAGE
(TOP VIEW)
The UCC2918 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.
1
24
23
22
21
20
19
18
17
16
15
14
13
VIN
VIN
VIN
VOUT
VOUT
VOUT
VOUT
GND*
GND*
GND*
GND*
GND*
NC
2
3
4
VIN
5
GND*
GND*
GND*
GND*
GND*
FAULT
6
7
8
9
10
11
12
SHTDWN
IFAULT
CT
IMAX
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.
Pin 9 serves as the lowest impedance to the electrical
ground. Pins 5, 6, 7, 8, 16, 17, 18, 19, and 20 serve as
heat sink/ground.
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 UCC2918 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 UCC2918 can also be put into the sleep mode, drawing
only 1 µA of supply current.
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.
Copyright 2000, Texas Instruments Incorporated
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1
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