1
LTC 690/LTC 691
LTC 694/LTC 695
Microprocessor
Supervisory C ircuits
ADJ
V
IN
V
OUT
10
μ
F
V
IN
≥
7.5V
5V
100
μ
F
0.1
μ
F
μ
P NMI
μ
P
POWER
POWER TO
CMOS RAM
I/O LINE
μ
P RESET
μ
P
SYSTEM
0.1
μ
F
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
0.1
μ
F
100
+
+
RESET Output Voltage vs
Supply Voltage
I
UL Recognized File # E145770
I
GuaranteedReset Assertion at V
CC
= 1V
I
1.5mA Maximum Supply Current
I
Fast (35ns Max) Onboard Gating of RAM Chip
Enable Signals
I
SO-8 and S16 Packaging
I
4.65V Precision Voltage Monitor
I
Power OK/Reset Time Delay: 50ms, 200ms
or Adjustable
I
Minimum External Component Count
I
1
μ
A Maximum Standby Current
I
Voltage Monitor for Power-Fail
or Low-Battery Warning
I
Thermal Limiting
I
Performance Specified Over Temperature
I
Superior Upgrade for MAX690 Family
The LTC
690 family provides complete power supply
monitoring and battery control functions for microproces-
sor 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 time-out
period.
I
Critical
μ
P Power Monitoring
I
Intelligent Instruments
I
Battery-Powered Computers and Controllers
I
Automotive Systems
SUPPLY VOLTAGE (V)
0
R
3
4
5
4
2
1
0
1
2
3
5
T
= 25
°
C
EXTERNAL PULL-UP = 10
μ
A
V
BATT
= 0V
690 TA02
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
DESCRIPTIO
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APPLICATIO S
U
TYPICAL APPLICATIO
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