Datasheet

LTC694-3.3/LTC695-3.3
15
69453fb
TYPICAL APPLICATION
Capacitor Back-Up with 74HC4016 Switch
TYPICAL APPLICATION
R1
10k
R2
30k
0.1µF
0.1µF
14121110
1
7
100µF
13
2
3.3V
V
CC
V
OUT
V
BATT
74HC4016
694/5-3.3 TA03
LOW LINE
GND
LTC695-3.3
+
Table 2. LTC695-3.3 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) LTC695-3.3
Low External Clock Input 1024 CLKs 4096 CLKs 2048 CLKs
Low External Capacitor*
400ms
70pF
•C
1.6s
70pF
•C
800ms
70pF
•C
Floating or High Low 100ms 1.6 sec 200ms
Floating or High Floating or High 1.6 sec 1.6 sec 200ms
*The nominal internal frequency is 10.24kHz. The nominal oscillator frequency with external capacitor is f
OSC
(Hz) =
184,000
C(pF) • 1025
the internal oscillator is enabled and the reset active time
is fixed at 140ms minimum for the LTC695-3.3. 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.
Push-Button Reset
The LTC694-3.3/LTC695-3.3 do not provide a logic input
for direct connection to a push-button. However, a push-
button in series with a 100 resistor connected to the
RESET output pin (Figure 13) provides an alternative for
manual reset. Connecting a 0.1µF capacitor to the RESET
pin debounces the push-button input.
The 100 resistor in series with the push-button is re-
quired to prevent the ringing, due to the capacitance and
lead inductance, from pulling the RESET pins of the MPU
and LTC69X below ground.
3.3V
100
V
CC
LTC694-3.3
LTC695-3.3
GND
694/5-3.3 F13
RESET
0.1µF
MPU
(e.g. 68HC05)
RESET
Figure 13. The External Push-Button Reset