LTC690/LTC691
LTC694/LTC695
Microprocessor
Supervisory Circuits
Features
Description
Guaranteed Reset Assertion at VCC = 1V
n 1.5mA Maximum Supply Current
n Fast (35ns Max) Onboard Gating of RAM Chip
Enable Signals
n SO-8 and S16 Packaging
n 4.65V Precision Voltage Monitor
n Power OK/Reset Time Delay: 50ms, 200ms
or Adjustable
n Minimum External Component Count
n 1µA Maximum Standby Current
n Voltage Monitor for Power-Fail
or Low Battery Warning
n Thermal Limiting
n Performance Specified Over Temperature
n Superior Upgrade for MAX690 Family
The LTC®690 family, LTC690/LTC691/LTC694/LTC695,
provides complete power supply monitoring and battery
control functions for microprocessor reset, battery backup, 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
logic low even with VCC as low as 1V.
n
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.
Applications
n
n
n
n
For an early warning of impending power failure, the LTC690
family provides an internal comparator with a user-defined
threshold. An internal watchdog timer is also available, which
forces the reset pins to active states when the watchdog
input is not toggled prior to a preset timeout period.
Critical µP Power Monitoring
Intelligent Instruments
Battery-Powered Computers and Controllers
Automotive Systems
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
+
VIN
10µF
VOUT
ADJ
5
5V
+
100µF
0.1µF
3V
VCC
VOUT
LTC690/LTC691
LTC694/LTC695
VBATT
POWER TO
µP
0.1µF CMOS RAM POWER
µP
SYSTEM
µP RESET
RESET
51k
µP NMI
PFO
PFI
I/O LINE
GND WDI
10k
0.1µF
100Ω
MICROPROCESSOR RESET, BATTERY BACK-UP, POWER FAILURE
WARNING AND WATCHDOG TIMING ARE ALL IN A SINGLE CHIP
FOR MICROPROCESSOR SYSTEMS
690 TA01
RESET OUTPUT VOLTAGE (V)
LT®1086-5
VIN ≥ 7.5V
RESET Output Voltage
vs Supply Voltage
TA = 25°C
EXTERNAL PULL-UP = 10µA
VBATT = 0V
4
3
2
1
0
0
1
3
4
2
SUPPLY VOLTAGE (V)
5
690 TA02
690ff
For more information www.linear.com/690
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