LTC694-3.3/LTC695-3.3
3.3V Microprocessor
Supervisory Circuits
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FEATURES
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DESCRIPTIO
UL Recognized
File # E145770
Guaranteed Reset Assertion at VCC = 1V
Pin Compatible with LTC694/LTC695
for 3.3V Systems
200µA Typical Supply Current
Fast (30ns Typ) On-Board Gating of
RAM Chip Enable Signals
SO-8 and S16 Packages
2.90V Precision Voltage Monitor
Power OK/Reset Time Delay: 200ms or Adjustable
Minimum External Component Count
1µA Maximum Standby Current
Voltage Monitor for Power-Fail or
Low-Battery Warning
Thermal Limiting
Performance Specified Over Temperature
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APPLICATIO S
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The LTC®694-3.3/LTC695-3.3 provide complete 3.3V
power supply monitoring and battery control functions.
These include power-on reset, battery back-up, RAM write
protection, power failure warning and watchdog timing.
The devices are pin compatible upgrades of the LTC694/
LTC695 that are optimized for 3.3V systems. Operating
power consumption has been reduced to 0.6mW (typical)
and 3µW maximum in battery back-up mode. Microprocessor reset and memory write protection are provided
when the supply falls below 2.9V. The RESET output is
guaranteed to remain logic low with VCC as low as 1V.
The LTC694-3.3/LTC695-3.3 power the active RAMs with
a charge pumped NMOS power switch to achieve low
dropout 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
LTC694-3.3/LTC695-3.3 provide 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.
3.3V Low Power Systems
Critical µP Power Monitoring
Intelligent Instruments
Battery-Powered Computers and Controllers
Automotive Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATIO
LT1129-3.3
VIN
VOUT
+
1µF
OUT SENSE
5
3.3V
VCC
+
100µF
0.1µF
SHDN
GND
LTC695-3.3
VBATT
2.4V
51k
PFI
18k
MICROPROCESSOR RESET, BATTERY BACK-UP,
RAM WRITE PROTECTION, POWER WARNING AND
WATCHDOG TIMING ARE ALL IN A SINGLE CHIP
FOR 3.3V MICROPROCESSOR SYSTEM
VOUT
CE IN
CE OUT
RESET
PFO
GND WDI
POWER TO
µP
CMOS RAM POWER
0.1µF
µP
SYSTEM
DECODER OUTPUT
RAM CS
µP RESET
µP NMI
I/O LINE
100Ω
0.1µF
RESET OUTPUT VOLTAGE (V)
VIN ≥ 5V
RESET Output Voltage vs
Supply Voltage
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3
2
1
0
694/5-3.3 TA01
0
1
3
4
2
SUPPLY VOLTAGE (V)
5
694/5-3.3 TA02
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