LTC690/ LTC691
LTC694/ LTC695
Mic ro p ro c e sso r
Sup e rviso ry Circ uits
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FEATURES
DESCRIPTIO
The LTC®690 family provides complete power supply
monitoringandbatterycontrolfunctions formicroproces-
sor reset, battery back-up, CMOS RAM write protection,
power failure warning and watchdog timing. A precise
internal voltage reference and comparator circuit monitor
thepowersupplyline. Whenanout-of-tolerancecondition
occurs,theresetoutputs areforcedtoactivestates andthe
chipenableoutputunconditionallywrite-protects external
memory. In addition, the RESET output is guaranteed to
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UL Recognized
Guaranteed Reset Assertion at V = 1V
1.5mA Maximum Supply Current
Fast (35ns Max) Onboard Gating of RAM Chip
Enable Signals
File # E145770
®
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CC
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SO-8 and S16 Packaging
4.65V Precision Voltage Monitor
Power OK/Reset Time Delay: 50ms, 200ms
or Adjustable
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Minimum External Component Count
1µA Maximum Standby Current
Voltage Monitor for Power-Fail
or Low-Battery Warning
Thermal Limiting
Performance Specified Over Temperature
Superior Upgrade for MAX690 Family
remain logic low even with V as low as 1V.
CC
The LTC690 family powers the active CMOS RAMs with a
charge pumped NMOS power switch to achieve low drop-
out and low supply current. When primary power is lost,
auxiliarypower,connectedtothebatteryinputpin,powers
the RAMs in standby through an efficient PMOS switch.
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For an early warning of impending power failure, the
LTC690 family provides an internal comparator with a
user-definedthreshold. Aninternalwatchdogtimeris also
available, which forces the reset pins to active states when
thewatchdoginputis nottoggledpriortoapresettime-out
period.
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APPLICATIO S
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Critical µP Power Monitoring
Intelligent Instruments
Battery-Powered Computers and Controllers
Automotive Systems
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, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
RESET Output Voltage vs
Supply Voltage
5
LT®1086-5
T
= 25°C
A
V
IN
≥ 7.5V
5V
EXTERNAL PULL-UP = 10µA
= 0V
POWER TO
CMOS RAM POWER
µP
V
IN
V
OUT
V
CC
V
OUT
V
BATT
+
+
4
3
0.1µF
0.1µF
LTC690/LTC691
LTC694/LTC695
V
BATT
100µF
10µF
ADJ
µP
SYSTEM
3V
µP RESET
µP NMI
RESET
PFO
51k
10k
2
1
0
I/O LINE
PFI
WDI
GND
690 TA01
0.1µF
100Ω
MICROPROCESSOR RESET, BATTERY BACK-UP, POWER FAILURE
WARNING AND WATCHDOG TIMING ARE ALL IN A SINGLE CHIP
FOR MICROPROCESSOR SYSTEMS
0
1
2
3
4
5
SUPPLY VOLTAGE (V)
690 TA02
1