4

LTC699

S

APPLICATI

I FOR ATIO

Figure 1. Reset Active Time

Watchdog Timer

The LTC699 provides a watchdog timer function to moni-

tor the activity of the microprocessor. If the microproces-

sor does not toggle the Watchdog Input (WDI) within the

time-out period, RESET is forced to active low for a

minimum of 140ms. The watchdog time-out period is

fixed at a 1.0 second minimum on the LTC699, which is

adequate time for most systems to service the watchdog

timer immediately after a reset. Figure 2 shows the timing

diagram of watchdog time-out period and reset active

time. The watchdog time-out period is restarted as soon

as RESET is inactive. When either a high-to-low or low-to-

high transition occurs at the WDI pin prior to time-out, the

watchdog time is reset and begins to time out again. To

ensure the watchdog time does not time out, either a high-

to-low or low-to-high transition on the WDI pin must

occur at or less than the minimum time-out period. If the

input to the WDI pin remains either high or low, reset

pulses will be issued every 1.6 seconds typically. The

watchdog time can be deactivated by floating the WDI pin.

voltage threshold.

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7487

© LINEAR TECHNOLOGY CORPORATION 1992

LT/GP 0192 10K REV 0

110

°C 180°C/W

CONDITIONS: PCB MOUNT ON FR4 MATERIAL,

STILL AIR AT 25

°C, COPPER TRACE

110

°C 130°C/W

t1

t1 = RESET ACTIVE TIME

V1 = RESET VOLTAGE THRESHOLD

V2 = RESET VOLTAGE THRESHOLD +

RESET THRESHOLD HYSTERESIS

t1

V2

V2

V1

V1

LTC699 F01

RESET

t1 = RESET ACTIVE TIME

t2 = WATCHDOG TIME-OUT PERIOD

t2

t1

t1

WDI

RESET

LTC699 F02

t2

t1

Figure 2. Watchdog Time-Out Period and Reset Active Time

PACKAGE DESCRIPTIO

Dimensions in inches (millimeters) unless otherwise noted.

N8 Package

8-Lead Plastic DIP

S8 Package

8-Lead Plastic SOIC

N8 1191

E

C

12

3

4

8

76

5

D

S

L

A

B

SYMBOL

A

B

C

D

E

INCHES

0.130 ± 0.006

0.020 MIN

0.018 ± 0.003

0.045 – 0.065

0.009 – 0.015

0.400 MAX

0.300 – 0.320

MILLIMETERS

3.302 ± 0.127

0.508 MIN

0.457 ± 0.076

1.143 – 1.651

0.229 – 0.381

10.160 MAX

7.620 – 8.128

SYMBOL

L

S

INCHES

0.250 ± 0.010

0.325 + 0.025

–0.015

0.100 ± 0.010

0.125 MIN

0.065 TYP

0.045 ± 0.015

MILLIMETERS

6.350 ± 0.254

8.255 + 0.635

–0.381

2.540 ± 0.254

3.175 MIN

1.651 TYP

1.143 ± 0.381

h

× 45°

S8 1191

α

C

L

A

B

1

2

3

4

8

7

6

5

H

D

E

SYMBOL

A

B

C

D

E

INCHES

0.053 – 0.069

0.004 – 0.010

0.014 – 0.019

0.008 – 0.010

0.189 – 0.197

0.150 – 0.157

MILLIMETERS

1.346 – 1.753

0.102 – 0.254

0.356 – 0.483

0.203 – 0.254

4.801 – 5.004

3.810 – 3.988

SYMBOL

e

H

h

L

α

INCHES

0.050 TYP

0.228 – 0.244

0.010 – 0.020

0.016 – 0.050

MILLIMETERS

1.270 TYP

5.791 – 6.198

0.254 – 0.508

0.406 – 1.270

0° – 8° TYP