UCC1946

UCC2946

UCC3946

SLUS247B - FEBRUARY 2000

FEATURES

•

Fully Programmable Reset Threshold

•

Fully Programmable Reset Period

•

Fully Programmable Watchdog Period

•

2% Accurate Reset Threshold

•

VDD Can Go as Low as 2V

•

18

µA Maximum IDD

•

Reset Valid Down to 1V

Microprocessor Supervisor with Watchdog Timer

6

7

WDI

WP

8

VDD

3RES

5

POWER TO

CIRCUITRY

A3

A2

A1

A0

CLK

CLR

8-BIT COUNTER

400nA

WDO

1

GND

EDGE DETECT

WATCHDOG TIMING

100mV

1.235V

2

RTH

4

RP

1.235V

.

400nA

POWER ON RESET

BLOCK DIAGRAM

Note: Pinout represents the 8-pin TSSOP package.

UDG-98001

DESCRIPTION

The UCC3946 is designed to provide accurate microprocessor supervi-

sion, including reset and watchdog functions. During power up, the IC

asserts a reset signal RES with VDD as low as 1V. The reset signal re-

mains asserted until the VDD voltage rises and remains above the re-

set threshold for the reset period. Both reset threshold and reset period

are programmable by the user. The IC is also resistant to glitches on

the VDD line. Once RES has been deasserted, any drops below the

threshold voltage need to be of certain time duration and voltage mag-

nitude to generate a reset signal. These values are shown in Figure 1.

An I/O line of the microprocessor may be tied to the watchdog input

(WDI) for watchdog functions. If the I/O line is not toggled within a set

watchdog period, programmable by the user, WDO will be asserted.

The watchdog function will be disabled during reset conditions.

The UCC3946 is available in 8-pin SOIC(D), 8-pin DIP (N or J) and

8-pin TSSOP(PW) packages to optimize board space.