LTC690 Linear Technology, LTC690 Datasheet - Page 13

• Manufacturer Part Number: LTC690
• Description: Microprocessor Supervisory Circuits
• Manufacturer: Linear Technology

A
The LTC691 and LTC695 provide an additional output
(Watchdog Output, WDO) which goes low if the watchdog
timer is allowed to time out and remains low until set high
by the next transition on the WDI pin. WDO is also set high
when V
The LTC691 and LTC695 have two additonal pins OSC SEL
and OSC IN, which allow reset active time and watchdog
time-out period to be adjusted per Table 2. Several con-
figurations are shown in Figure 12.
OSC IN can be driven by an external clock signal or an
external capacitor can be connected between OSC IN and
PPLICATI
CC
falls below the reset voltage threshold or V
RESET
WDO
V
WDI
CC
O
= 5V
U
S
5V
5V
I FOR ATIO
U
4
4
3
3
1.6 SECOND WATCHDOG
INTERNAL OSCILLATOR
GND
GND
V
V
EXTERNAL CLOCK
CC
CC
t
Figure 11. Watchdog Time-Out Period and Reset Active Time
1
LTC691
LTC695
LTC691
LTC695
W
OSC SEL
OSC SEL
OSC IN
OSC IN
Figure 12. Oscillator Configurations
7
8
8
7
t
2
U
FLOATING
OR HIGH
FLOATING
OR HIGH
BATT
t
1
t
t
t
.
1
2
3
= RESET ACTIVE TIME
= NORMAL WATCHDOG TIME-OUT PERIOD
= WATCHDOG TIME-OUT PERIOD IMMEDIATELY
AFTER A RESET
GND when OSC SEL is forced low. In these configurations,
the nominal reset active time and watchdog time-out
period are determined by the number of clocks or set by
the formula in Table 2. When OSC SEL is high or floating,
the internal oscillator is enabled and the reset active time
is fixed at 35ms minimum for the LTC691 and 140ms
minimum for the LTC695. OSC IN selectes between the 1
second and 70ms minimum normal watchdog time-out
periods. In both cases, the time-out period immediately
after a reset is at least 1 second.
5V
t
5V
3
4
3
4
3
EXTERNAL OSCILLATOR
INTERNAL OSCILLATOR
GND
100ms WATCHDOG
V
V
GND
CC
CC
LTC691
LTC695
LTC691
LTC695
OSC SEL
OSC SEL
OSC IN
OSC IN
8
7
LTC694/LTC695
8
LTC690/LTC691
7
FLOATING
OR HIGH
690 F12
690 F11
13