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LTC693I

Microprocessor Supervisory Circuits

Linear Technology 

LTC692/LTC693

APPLICATI S I FOR ATIO

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

WATCHDOG TIME-OUT PERIOD

OSC SEL

OSC IN

NORMAL

(Short Period)

IMMEDIATELY

AFTER RESET

(Long Period)

RESET ACTIVE TIME

LTC693

Low

Low

Floating or High

Floating or High

External Clock Input

External Capacitor*

Low

Floating or High

1024 clks

400ms

47pF

×C

100ms

1.6 sec

4096 clks

1.6 sec

47pF

×

C

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)

2048 clks

800ms

47pF

×

C

200ms

200ms

Pushbutton Reset

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

connection to a pushbutton. However, a pushbutton in

series with a 100Ω 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 pushbutton input.

The 100Ω 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.

5V

VCC

RESET

LTC692

LTC693

GND

0.1µF

100Ω

RESET

MPU

(e.g. 6805)

LTC692/3 • F13

Figure 13. The External Pushbutton Reset

TYPICAL APPLICATI S

Capacitor Backup with 74HC4016 Switch

5V

VCC

VOUT

0.1µF

R1

10k

10 11 12 14

LTC693

1 74HC4016

2

VBATT LOW LINE

R2

30k

7

13

+

100µF

GND

0.1µF

LTC692/3 • TA3

14

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