Datasheet
LTC692/LTC693
15
0692fb
APPLICATIONS INFORMATION
The LTC693 provides 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
CC
falls below the reset voltage threshold or V
BATT
.
The LTC693 has two additional pins OSC SEL and
OSC IN, which allow reset active time and watchdog
timeout period to be adjusted per Table 2. Several con-
fi gurations 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
GND when OSC SEL is forced low. In these confi gura-
tions, the nominal reset active time and watchdog timeout
period are determined by the number of clocks or set by
the formula in Table 2. When OSC SEL is high or fl oating,
the internal oscillator is enabled and the reset active time
is fi xed at 140ms minimum. OSC IN selects between the
1 second and 70ms minimum normal watchdog timeout
periods. In both cases, the timeout period immediately
after a reset is at least 1 second.
EXTERNAL CLOCK
INTERNAL OSCILLATOR
1.6 SECOND WATCHDOG
INTERNAL OSCILLATOR
100ms WATCHDOG
EXTERNAL OSCILLATOR
GND
GND GND
GND
V
CC
V
CC
V
CC
OSC SEL
OSC SEL
OSC SEL
OSC SEL
OSC IN
OSC IN
OSC IN
OSC IN
3
3
3
3
4
4
4
4
8
8
8
8
7
7
7
7
V
CC
FLOATING
OR HIGH
FLOATING
OR HIGH
LTC693
FLOATING
OR HIGH
LTC693
LTC693
LTC693
692_3 • F12
5V
5V
5V
5V
Figure 12. Oscillator Confi gurations
Table 2. LTC693 Reset Active Time and Watchdog Timeout Selections
OSC SEL OSC IN
WATCHDOG TIMEOUT PERIOD RESET ACTIVE TIME
NORMAL (SHORT PERIOD)
IMMEDIATELY AFTER RESET
(LONG PERIOD) LTC693
Low External Clock Input 1024 clks 4096 clks 2048 clks
Low External Capacitor*
400ms
47pF
s C
1.6 sec
47pF
s C
800ms
47pF
s C
Floating or High Low 100ms 1.6 sec 200ms
Floating or High Floating or High 1.6 sec 1.6 sec 200ms
184,000
C (pF)
*The nominal internal frequency is 10.24kHz. The nominal oscillator frequency with external capacitor is f
OSC
(Hz) =