UCC2918

UCC3918

SLUS384A - NOVEMBER 1999

FEATURES

• Integrated 0.06Ω Power

MOSFET

• 3V to 6V Operation

• External Analog control of

Fault Current from 0A to 4A

• Independent Analog Control

of Current Limit up to 5A

• Fast Overload Protection

• Uni-directional Switch

• Minimal External Components

• Programmable On Time

• Programmable Start Delay

• Fixed 3% Duty Cycle

Low On Resistance Hot Swap Power Manager

9

8

5

4

13

12

10

6

7

3

2

1

INTERNAL

BIAS

THERMAL

SHUTDOWN

ON TIME

CONTROL

3% DUTY

CYCLE

CHARGE

PUMP

16

15

14

+

–

VIN

VIN

VIN

VOUT

VOUT

VOUT

SHTDWN

FAULT

CT

HEAT SINK GND

PINS

GND

IFAULT

IMAX

CURRENT

FAULT LEVEL

OVERLOAD

COMPARATOR

OVERCURRENT

COMPARATOR

REVERSE

COMPARATOR

V

OUT

+

20mV

CURRENT SENSE

1.5V

H = OPEN

MAXIMUM

CURRENT

LEVEL

+

BLOCK DIAGRAM

UDG-99153

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 tim-

ing capacitor, and 2 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 0A to 4A.

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 cur-

rent 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 0.06

Ω. When the output current exceeds the fault level

or the maximum sourcing level, the output remains on, but the fault timer starts

charging 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 form a switch to a

constant current source.

(continued)

application

INFO

available