UCC3918

LOW ONRESISTANCE HOT SWAP POWER MANAGER

SLUS384B – NOVEMBER 1999 – REVISED JUNE 2000

1

www.ti.com

D Integrated 0.075-Ω Power MOSFET

D 3 V to 6 V Operation

D External Analog Control of Fault Current

from 0 A to 4 A

D Independent Analog Control of Current

Limit Up to 5 A

D Fast Overload Protection

D Unidirectional Switch

D Minimal External Components

D 1-µA ICC When Disabled

D Programmable On Time

D Programmable Start Delay

D 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 (CT). Once CT charges to a preset

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.

Copyright

 2000, Texas Instruments Incorporated

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

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.

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.

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

VIN

VIN

VIN

GND*

GND*

FAULT

SHTDWN

IFAULT

VOUT

VOUT

VOUT

GND*

GND*

NC

CT

IMAX

DP PACKAGE

(TOP VIEW)