4
LTC699
U
S
A
O
PP
L
IC
AT
I
WU
U
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.
The timer is also disabled when V
CC
falls below the reset
voltage threshold.
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900
●
FAX
: (408) 434-0507
●
TELEX
: 499-3977
LINEAR TECHNOLOGY CORPORATION 1992
LT/GP 0192 10K REV 0
T
JMAX
θ
JA
110°C 180°C/W
CONDITIONS: PCB MOUNT ON FR4 MATERIAL,
STILL AIR AT 25°C, COPPER TRACE
T
JMAX
θ
JA
110°C 130°C/W
V
CC
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
V
CC
= 5V
t2
t1
t1
WDI
RESET
LTC699 F02
t2
t1
Figure 2. Watchdog Time-Out Period and Reset Active Time
PACKAGE DESCRIPTIO
U
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead Plastic DIP
S8 Package
8-Lead Plastic SOIC
N8 1191
E
C
e
A
12
3
4
8
76
5
E
1
D
Q
1
B
1
e
1
S
A
1
L
A
B
SYMBOL
A
A
1
B
B
1
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
E
1
e
A
e
1
L
Q
1
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
e
1
A
1
1
2
3
4
8
7
6
5
H
D
E
SYMBOL
A
A
1
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
