Datasheet

Figure 11. Backup VBattery Monitor with Optional Test Load
Figure 13. Disabling the Watchdog Under Program Control
Figure 12. Adding Hysteresis to the Power-Fail Voltage
Comparator
Figure 14. Selecting Internal or External Watchdog Timeout
MAX690
MAX691
MAX692
MAX693
MAX694
MAX695
PFI
R
L
V
BATT
CE OUT
LOW BATTERY
SIGNAL TO
µP I/O PIN
FROM µP
I/O PIN
GND
LOW
APPLIES
LOAD
TO BATTERY
+5V
V
CC
CE IN
10MΩ
10MΩ
PFO
MAX690
MAX691
MAX692
MAX693
MAX694
MAX695
WDI
WATCHDOG
STROBE
GND
+5V
V
CC
WATCHDOG
DISABLE
EN
MAX690
MAX691
MAX692
MAX693
MAX694
MAX695
PFO
V
CC
PFI
GND
TO P
7805
+5V7V TO 15V
R4
10kΩ
R1
75kΩ
R2
13kΩ
V
H
= 9.125V
V
L
= 7.9V
HYSTERESIS = 1.23V
V
H
= 1.3V
(
1 + +
)
R3
300kΩ
R1
R2
R1
R3
R1
R3
V
L
= 1.3V
(
1 + -
)
HYSTERESIS 5V x
ASSUMING R4 < < R3
R1
R2
(5V -1.3V) R1
1.3V (R3 + R4)
MAX691
MAX693
OSC SEL
LOW = INTERNAL
WATCHDOG TIMEOUT
HI = EXTERNAL
WATCHDOG
TIMEOUE
GND
+5V
V
CC
OSC IN
CONNECT FOR
100ms TIMEOUT
WHEN INTERNAL
TIMEOUT IS
SELECTED
CONNECT FOR
1.6s INTERNAL
TIMEOUT
MAX690–MAX695 Microprocessor Supervisory Circuits
www.maximintegrated.com
Maxim Integrated │ 14