LTC690M View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC690M' PDF : 16 Pages View PDF
LTC690/LTC691
LTC694/LTC695
APPLICATI S I FOR ATIO
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 VCC falls below the reset voltage threshold or VBATT.
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
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.
VCC = 5V
WDI
WDO
t1 = RESET ACTIVE TIME
t2 = NORMAL WATCHDOG TIME-OUT PERIOD
t3 = WATCHDOG TIME-OUT PERIOD IMMEDIATELY
AFTER A RESET
RESET
t2
t3
t1
t1
690 F11
Figure 11. Watchdog Time-Out Period and Reset Active Time
EXTERNAL CLOCK
3
5V
VCC
8
OSC SEL
LTC691
LTC695
4
GND
7
OSC IN
EXTERNAL OSCILLATOR
5V
3
VCC
8
OSC SEL
LTC691
LTC695
4
GND
7
OSC IN
INTERNAL OSCILLATOR
1.6 SECOND WATCHDOG
5V 3 VCC
8
OSC SEL
FLOATING
OR HIGH
LTC691
LTC695
4
GND
7 FLOATING
OSC IN
OR HIGH
INTERNAL OSCILLATOR
100ms WATCHDOG
3
5V
VCC
8
OSC SEL
FLOATING
OR HIGH
LTC691
LTC695
4 GND
OSC IN 7
690 F12
Figure 12. Oscillator Configurations
13
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