14

LTC692/LTC693

Low

External Clock Input

1024 clks

4096 clks

2048 clks

Low

External Capacitor*

Floating or High

Low

100ms

1.6 sec

200ms

Floating or High

Floating or High

1.6 sec

1.6 sec

200ms

S

APPLICATI

I FOR ATIO

OSC IN

OSC SEL

Pushbutton Reset

The LTC692/LTC693 do not provide a logic input for direct

connection to a pushbutton. However, a pushbutton in

series with a 100

ΩresistorconnectedtotheRESEToutput

pin (Figure 13) provides an alternative for manual reset.

Connecting a 0.1

µF capacitor to the RESET pin debounces

the pushbutton input.

The 100

Ω resistor in series with the pushbutton is re-

quired to prevent the ringing, due to the capacitance and

lead inductance, from pulling the RESET pins of the MPU

and LTC692/LT693 below ground.

Figure 13. The External Pushbutton Reset

184,000

C(pF)

WATCHDOG TIME-OUT PERIOD

RESET ACTIVE TIME

IMMEDIATELY

AFTER RESET

(Long Period)

NORMAL

(Short Period)

LTC693

Table 2. LTC693 Reset Active Time and Watchdog Time-Out Selections

400ms × C

47pF

1.6 sec × C

47pF

800ms × C

47pF

5V

100

Ω

LTC692

LTC693

GND

LTC692/3 • F13

RESET

0.1

µF

MPU

(e.g. 6805)

RESET

S

APPLICATI

TYPICAL

Capacitor Backup with 74HC4016 Switch

R1

10k

R2

30k

0.1

µF

0.1

µF

+

14

12

11

10

1

7

100

µF

13

2

5V

74HC4016

LTC692/3 • TA3

LOW LINE

GND

LTC693