MAX690 Просмотр технического описания (PDF) - Maxim Integrated
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MAX690 Datasheet PDF : 18 Pages
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MAX690–MAX695
Microprocessor Supervisory Circuits
+5V
10MΩ
10MΩ
RL
VBATT
PFI
VCC
MAX690
MAX691
MAX692
MAX693
MAX694
MAX695
CE OUT
GND
LOW BATTERY
PFO
SIGNAL TO
µP I/O PIN
LOW
CE IN
APPLIES
FROM µP
I/O PIN
LOAD
TO BATTERY
Figure 11. Backup VBattery Monitor with Optional Test Load
7V TO 15V
7805
R1
75kΩ
+5V
VCC
R4
10kΩ
PFO
MAX690
MAX691
MAX692
MAX693
MAX694
MAX695
R2
13kΩ
R3
300kΩ
VH = 9.125V
VL = 7.9V
HYSTERESIS = 1.23V
PFI
GND
TO P
( ) VH = 1.3V 1 +RR12 +RR13
( ) VL = 1.3V
1 +R1 -(5V -1.3V) R1
R2 1.3V (R3 + R4)
HYSTERESIS
5V
x
R1
R3
ASSUMING R4 < < R3
Figure 12. Adding Hysteresis to the Power-Fail Voltage
Comparator
+5V
+5V
WATCHDOG
STROBE
EN
WATCHDOG
DISABLE
VCC
MAX690
MAX691
WDI MAX692
MAX693
MAX694
MAX695
GND
Figure 13. Disabling the Watchdog Under Program Control
LOW = INTERNAL
WATCHDOG TIMEOUT
HI = EXTERNAL
WATCHDOG
TIMEOUE
CONNECT FOR
100ms TIMEOUT
WHEN INTERNAL
TIMEOUT IS
SELECTED
VCC
OSC SEL
MAX691
MAX693
OSC IN
GND
CONNECT FOR
1.6s INTERNAL
TIMEOUT
Figure 14. Selecting Internal or External Watchdog Timeout
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