LTC690/LTC691
LTC694/LTC695
Microprocessor
Supervisory Circuits
FeaTures
DescripTion
The LTC®690 family, LTC690/LTC691/LTC694/LTC695,
provides complete power supply monitoring and battery
control functions for microprocessor reset, battery back-
up, CMOS RAM write protection, power failure warning
and watchdog timing. A precise internal voltage reference
and comparator circuit monitor the power supply line.
When an out-of-tolerance condition occurs, the reset
outputs are forced to active states and the chip enable
output unconditionally write-protects external memory.
In addition, the RESET output is guaranteed to remain
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Guaranteed Reset Assertion at V = 1V
CC
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1.5mA Maximum Supply Current
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Fast (35ns Max) Onboard Gating of RAM Chip
Enable Signals
SO-8 and S16 Packaging
4.65V Precision Voltage Monitor
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n
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Power OK/Reset Time Delay: 50ms, 200ms
or Adjustable
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Minimum External Component Count
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1µA Maximum Standby Current
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Voltage Monitor for Power-Fail
logic low even with V as low as 1V.
CC
or Low Battery Warning
Thermal Limiting
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,
auxiliary power, connected to the battery input pin, powers
the RAMs in standby through an efficient PMOS switch.
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Performance Specified Over Temperature
Superior Upgrade for MAX690 Family
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applicaTions
Foranearlywarningofimpendingpowerfailure,theLTC690
family provides an internal comparator with a user-defined
threshold.Aninternalwatchdogtimerisalsoavailable,which
forces the reset pins to active states when the watchdog
input is not toggled prior to a preset timeout period.
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Critical µP Power Monitoring
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Intelligent Instruments
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Battery-Powered Computers and Controllers
Automotive Systems
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L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Typical applicaTion
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
µP
V
V
V
CC
V
IN
OUT
V
OUT
BATT
4
3
+
+
CMOS RAM POWER
0.1µF
3V
0.1µF
LTC690/LTC691
LTC694/LTC695
100µF
10µF
ADJ
µP
SYSTEM
V
BATT
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
690ff
1
For more information www.linear.com/690