LTC690 Datasheet, PDF (1/16 Pages) Linear Technology – Microprocessor Supervisory Circuits

FEATURES
s _{UL Recognized ® File # E145770}
s _{Guaranteed Reset Assertion at VCC = 1V}
s _{1.5mA Maximum Supply Current}
s _{Fast (35ns Max) Onboard Gating of RAM Chip}
Enable Signals
s _{SO-8 and S16 Packaging}
s _{4.65V Precision Voltage Monitor}
s _{Power OK/Reset Time Delay: 50ms, 200ms}
or Adjustable
s _{Minimum External Component Count}
s _{1µA Maximum Standby Current}
s _{Voltage Monitor for Power-Fail}
or Low-Battery Warning
s _{Thermal Limiting}
s _{Performance Specified Over Temperature}
s _{Superior Upgrade for MAX690 Family}
U
APPLICATIO S
s _{Critical µP Power Monitoring}
s _{Intelligent Instruments}
s _{Battery-Powered Computers and Controllers}
s _{Automotive Systems}
LTC690/LTC691
LTC694/LTC695
Microprocessor
Supervisory Circuits
DESCRIPTIO
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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
V_IN ≥ 7.5V
+
10µF
LT ^®1086-5
V_IN
V_OUT
ADJ
5V
+
100µF
51k
10k
0.1µF
3V
V_CC
V_OUT
LTC690/LTC691
LTC694/LTC695
V_BATT
RESET
PFO
PFI _GND WDI
0.1µF
MICROPROCESSOR RESET, BATTERY BACK-UP, POWER FAILURE
WARNING AND WATCHDOG TIMING ARE ALL IN A SINGLE CHIP
FOR MICROPROCESSOR SYSTEMS
0.1µF
POWER TO µP
CMOS RAM POWER
µP
SYSTEM
µP RESET
µP NMI
I/O LINE
100Ω
690 TA01
RESET Output Voltage vs
Supply Voltage
5
T_A = 25°C
EXTERNAL PULL-UP = 10µA
4 ^VBATT ^{= 0V}
3
2
1
0
0
1
2
3
4
5
SUPPLY VOLTAGE (V)
690 TA02
1