MAX690–MAX695
Microprocessor Supervisory Circuits
General Description
The MAX690 family of supervisory circuits reduces the
complexity and number of components required for
power supply monitoring and battery control functions in
microprocessor systems. These include µP reset and
backup-battery switchover, watchdog timer, CMOS RAM
write protection, and power-failure warning. The MAX690
family significantly improves system reliability and accuracy compared to that obtainable with separate ICs or
discrete components.
The MAX690, MAX692, and MAX694 are supplied in
8-pin packages and provide four functions:
●● A reset output during power-up, power-down, and
brownout conditions.
●● Battery backup switching for CMOS RAM, CMOS
microprocessor or other low power logic.
●● A Reset pulse if the optional watchdog timer has not
been toggled within a specified time.
●● A 1.3V threshold detector for power fail warning, low
battery detection, or to monitor a power supply other
than +5V.
Benefits and Features
●● Supervisory Function Integration Saves Board Space
while Fully Protecting Microprocessor-Based Systems
• Precision Voltage Monitor
-- 4.65V (MAX690, MAX691, MAX694, MAX695)
-- 4.40V (MAX692, MAX693)
• Power OK/Reset Time Delay
-- 50ms, 200ms, or Adjustable
• Watchdog Timer
-- 100ms, 1.6s, or Adjustable
• Battery Backup Power Switching
• Voltage Monitor for Power Fail or Low Battery
Warning
• Minimum External Component Count
●● Low Power Consumption in Battery Backup Mode
Extends Battery Life
• 1µA Standby Current
●● Onboard Gating of Chip Enable Signals Protects
Against Erroneous Data Written to RAM During Low
VCC Events
Applications
●● Write protection of CMOS RAM or EEPROM.
●●
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●●
●●
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●● Adjustable reset and watchdog timeout periods.
Ordering information appears at end of data sheet.
The MAX691, MAX693, and MAX695 are supplied in 16-pin
packages and perform all MAX690, MAX692, MAX694
functions, plus:
●● Separate outputs for indicating a watchdog timeout,
backup-battery switchover, and low VCC.
Computers
Controllers
Intelligent Instruments
Automotive Systems
Critical µP Power Monitoring
Pin Configurations
TOP VIEW
Typical Operating Circuit
VOUT 1
VCC 2
GND 3
MAX690
MAX692
MAX694
PFI 4
+5V
VOUT
VCC
VBATT
POWER TO
CMOS RAM
RESET
PFI
µP RESET
PFO
µP NMI
WDI
7 RESET
6 WDI
5 PFO
µP
POWER
µP
SYSTEM
MAX690
8 VBATT
I/O
LINE
VBATT 1
16 RESET
VOUT 2
VCC 3
GND 4
BATT ON 5
15 RESET
MAX691
MAX693
MAX695
14 WDO
13 CE IN
12 CE OUT
MAX690 TYPICAL APPLICATION
19-0218; Rev 5; 4/15
11 WDI
OSC IN 7
GND
LOW LINE 6
10 PFO
OSC SEL 8
9 PFI
