LTC693IN データシートの表示（PDF） - Linear Technology
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LTC693IN Datasheet PDF : 20 Pages
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LTC692/LTC693
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
VCC falls below the reset voltage threshold or VBATT.
The LTC693 has 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 140ms minimum. OSC IN selects 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.
EXTERNAL CLOCK
3
5V
VCC
8
OSC SEL
EXTERNAL OSCILLATOR
5V 3 VCC
8
OSC SEL
LTC693
4
GND
7
OSC IN
LTC693
4
GND
7
OSC IN
INTERNAL OSCILLATOR
1.6 SECOND WATCHDOG
3
5V
VCC
8
OSC SEL
FLOATING
OR HIGH
INTERNAL OSCILLATOR
100ms WATCHDOG
3
5V
VCC
8
OSC SEL
FLOATING
OR HIGH
LTC693
LTC693
4
GND
7
OSC IN
FLOATING
OR HIGH
4
GND
7
OSC IN
692_3 • F12
Figure 12. Oscillator Configurations
Table 2. LTC693 Reset Active Time and Watchdog Time-Out Selections
WATCHDOG TIME-OUT PERIOD
OSC SEL
OSC IN
IMMEDIATELY AFTER RESET
NORMAL (SHORT PERIOD)
(LONG PERIOD)
Low
External Clock Input
1024 clks
4096 clks
Low
External Capacitor*
400ms
47pF
s
C
1.6 sec
47pF
s
C
Floating or High
Floating or High
Low
Floating or High
100ms
1.6 sec
1.6 sec
1.6 sec
*The nominal internal frequency is 10.24kHz. The nominal oscillator frequency with external capacitor is fOSC (Hz) =
184,000
C (pF)
RESET ACTIVE TIME
LTC693
2048 clks
800ms
47pF
s
C
200ms
200ms
0692fa
15
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