LTC690CS8 Linear Technology, LTC690CS8 Datasheet - Page 15

• Manufacturer Part Number: LTC690CS8
• Description: IC MPU SUPERVISORY CIRCUIT 8SOIC
• Manufacturer: Linear Technology
• Type: Simple Reset/Power-On Resetr

Specifications of LTC690CS8

• Number Of Voltages Monitored: 1
• Output: Open Drain or Open Collector
• Reset: Active Low
• Reset Timeout: 35 ms Minimum
• Voltage - Threshold: 4.65V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS INFORMATION
Table 2. LTC691 and LTC695 Reset Active Time and Watchdog Timeout Selections
*The nominal internal frequency is 10.24kHz. The nominal oscillator frequency with external capacitor is f
Pushbutton Reset
The LTC690 family does 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 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 pushbutton reset as an extra feature.
Its pushbutton 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.
Floating or High
Floating or High
OSC SEL
Low
Low
External Clock Input
External Capacitor*
Floating or High
OSC IN
Low
(Short Period)
1024 clks
WATCHDOG TIME-OUT PERIOD
NORMAL
1.6 sec
100ms
Figure 14. The External Pushbutton Reset with the LTC1235
5V
(Long Period)
IMMEDIATELY
AFTER RESET
1 6
4096 clks
70
1.6 sec
1.6 sec
. sec
pF
V
LTC690/LTC691
LTC694/LTC695
Figure 13. The External Pushbutton Reset
CC
•
5V
C
GND
RESET
V
PBRST
CC
OSC
LTC1235
GND
(Hz) =
RESET
200
512 clks
70
LTC690/LTC691
LTC694/LTC695
LTC691
50ms
50ms
0.1μF
pF
ms
C pF •
184 000
( )
RESET ACTIVE TIME
•
C
,
100Ω
1025
RESET
(e.g. 6805)
MPU
RESET
(e.g. 6805)
MPU
690 F14
2048 clks
800
70
LTC695
200ms
200ms
690 F13
pF
ms
15
•
C
690fe