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
Table 2. LTC691 and LTC695 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
LTC691
LTC695
Low
Low
Floating or High
Floating or High
External Clock Input
External Capacitor*
Low
Floating or High
1024 clks
400ms
70pF
•
C
100ms
1.6 sec
4096 clks
1.6 sec
70pF
•
C
1.6 sec
1.6 sec
512 clks
200ms
70pF
•
C
50ms
50ms
2048 clks
800ms
70pF
•
C
200ms
200ms
*The nominal internal frequency is 10.24kHz. The nominal oscillator frequency with external capacitor is fOSC (Hz) =
184,000
C(pF) • 1025
Push-Button Reset
The LTC690 family does not provide a logic input for direct
connection to a pushbutton. However, a push-button 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 push-button input.
5V
VCC
RESET
LTC690/LTC691
LTC694/LTC695
GND
0.1µF
100Ω
RESET
MPU
(e.g. 6805)
690 F13
The 100Ω resistor in series with the push-button is
required to prevent the ringing, due to the capacitance and
lead inductance, from pulling the RESET pins of the MPU
and LTC69X below ground.
If a dedicated pushbutton reset input is desired, the
LTC1235 is a good choice (Figure 14). It has all the
functions of the LTC695 and provides push-button reset
as an extra feature. Its push-button is internally debounced
and invokes the normal 200ms reset sequence. This
eliminates the need for the 100Ω resistor and 0.1µF
capacitor. It also provides a more consistent reset pulse.
Figure 13. The External Push-Button Reset
5V
VCC RESET
LTC1235
PBRST
GND
RESET
MPU
(e.g. 6805)
690 F14
Figure 14. The External Push-Button Reset with the LTC1235
14
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