13

LTC692/LTC693

Figure 12. Oscillator Configurations

S

APPLICATI

I FOR ATIO

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

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 configurations

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.

Figure 11. Watchdog Time-out Period and Reset Active Time

t1 = RESET ACTIVE TIME

t2 = NORMAL WATCHDOG TIME-OUT PERIOD

t3 = WATCHDOG TIME-OUT PERIOD IMMEDIATELY

AFTER A RESET

t2

t3

t1

t1

WDO

WDI

RESET

LTC692/3 • F11

EXTERNAL CLOCK

INTERNAL OSCILLATOR

1.6 SECOND WATCHDOG

INTERNAL OSCILLATOR

100ms WATCHDOG

EXTERNAL OSCILLATOR

GND

GND

GND

GND

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

FLOATING

OR HIGH

FLOATING

OR HIGH

LTC693

FLOATING

OR HIGH

LTC693

LTC693

LTC693

LTC692/3 • F12

5V

5V

5V

5V