LTC690/LTC691
LTC694/LTC695
1
690ff
For more information www.linear.com/690
Typical applicaTion
FeaTures DescripTion
Microprocessor
Supervisory Circuits
The LT C
®
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
logic low even with V
CC
as low as 1V.
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.
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.
RESET Output Voltage
vs Supply Voltage
applicaTions
n
Guaranteed
Reset Assertion at V
CC
= 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
n
Critical µP Power Monitoring
n
Intelligent Instruments
n
Battery-Powered Computers and Controllers
n
Automotive Systems
L, LT , LT C , LT M, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
ADJ
V
IN
V
OUT
10µF
V
IN
≥ 7.5V
5V
100µF
0.1µF
µP NMI
µP
POWER
POWER TO
CMOS RAM
I/O LINE
µP RESET
µP
SYSTEM
0.1µF
3V
51k
10k
690 TA01
LT
®
1086-5
MICROPROCESSOR RESET, BATTERY BACK-UP, POWER FAILURE
WARNING AND WATCHDOG TIMING ARE ALL IN A SINGLE CHIP
FOR MICROPROCESSOR SYSTEMS
LTC690/LTC691
LTC694/LTC695
V
BATT
PFI
WDI
RESET
PFO
V
OUT
V
CC
GND
0.1µF 100Ω
++
SUPPLY VOLTAGE (V)
0
RESET OUTPUT VOLTAGE (V)
3
4
5
4
2
1
0
1
2
3
5
T
A
= 25°C
EXTERNAL PULL-UP = 10µA
V
BATT
= 0V
690 TA02
