7

LTC1232

sn1232 1232fas

soon as the reset outputs are inactive. When a high-to-low

transition occurs at the ST 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, a high-to low

transition on the ST pin must occur at or less than the

minimum time-out period. If the input to the ST pin

remains either high or low, reset pulses will be issued for

every time-out period selected by the TD pin. The watch-

point.

APPLICATIO S I FOR ATIO

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

condition is satisfied, the reset pulse generator forces the

reset outputs to active states. The reset signals will remain

active for a minimum of 250ms from the moment the

push-button reset input is released from logic low level

(see Timing Diagram).

Watchdog Timer

The LTC1232 provides a watchdog timer function to

monitor the activity of the microprocessor. If the micro-

processor does not stimulate the strobe input, ST, within

a selected time-out period, the reset outputs are forced to

active states for a minimum of 250ms. The time-out period

is selected by the Time-Out Delay input, TD, to be 150ms

with TD connected to GND, 600ms with TD left floating,

time-out period is adequate for many systems to serve 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

PACKAGE DESCRIPTIO

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-

tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

t1 = RESET ACTIVE TIME

t2 = WATCHDOG TIME-OUT PERIOD

t1

t2

LTC1232 • TA04

RST

ST

t2

t1

t1

N8 Package

8-Lead PDIP (Narrow .300 Inch)

(Reference LTC DWG # 05-08-1510)

N8 0502

.100

(2.54)

BSC

.065

(1.651)

TYP

.045 – .065

(1.143 – 1.651)

.130 ± .005

(3.302 ± 0.127)

.020

(0.508)

MIN

.018 ± .003

(0.457 ± 0.076)

.125

(3.175)

MIN

12

3

4

87

6

5

.255 ± .015*

(6.477 ± 0.381)

.400*

(10.160)

MAX

.009 – .015

(0.229 – 0.381)

.300 – .325

(7.620 – 8.255)

.325

+.035

–.015

+0.889

–0.381

8.255

()

NOTE:

1. DIMENSIONS ARE

INCHES

MILLIMETERS

*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .010 INCH (0.254mm)