LTC690 Linear Technology, LTC690 Datasheet - Page 14

• Manufacturer Part Number: LTC690
• Description: Microprocessor Supervisory Circuits
• Manufacturer: Linear Technology

LTC690/LTC691
LTC694/LTC695
A
*The nominal internal frequency is 10.24kHz. The nominal oscillator frequency with external capacitor is f
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 100 resistor connected to the RESET output
pin (Figure 13) provides an alternative for manual reset.
Connecting a 0.1 F capacitor to the RESET pin debounces
the push-button input.
The 100
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 100
capacitor. It also provides a more consistent reset pulse.
Table 2. LTC691 and LTC695 Reset Active Time and Watchdog Time-Out Selections
14
PPLICATI
Floating or High
Floating or High
OSC SEL
Low
Low
resistor in series with the push-button is
O
U
S
I FOR ATIO
U
External Clock Input
External Capacitor*
Floating or High
OSC IN
Low
W
resistor and 0.1 F
U
(Short Period)
WATCHDOG TIME-OUT PERIOD
NORMAL
1024 clks
400ms
1.6 sec
100ms
70pF
• C
Figure 14. The External Push-Button Reset with the LTC1235
5V
IMMEDIATELY
AFTER RESET
(Long Period)
1.6 sec
4096 clks
70pF
Figure 13. The External Push-Button Reset
1.6 sec
1.6 sec
V
LTC690/LTC691
LTC694/LTC695
5V
CC
• C
GND
V
PBRST
RESET
CC
OSC
LTC1235
GND
(Hz) =
RESET
200ms
512 clks
70pF
LTC691
50ms
50ms
C(pF) • 1025
0.1 F
184,000
RESET ACTIVE TIME
• C
100
RESET
(e.g. 6805)
MPU
800ms
2048 clks
70pF
690 F14
200ms
200ms
RESET
(e.g. 6805)
LTC695
MPU
• C
690 F13