LTC694-3.3_15 Datasheet, PDF (1/20 Pages) Linear Technology – 3.3V Microprocessor Supervisory Circuits

LTC694-3.3/LTC695-3.3
3.3V Microprocessor
Supervisory Circuits
FEATURES
n _{Guaranteed Reset Assertion at VCC = 1V}
n _{Pin Compatible with LTC694/LTC695 for 3.3V Systems}
n _{200μA Typical Supply Current}
n _{Fast (30ns Typ) Onboard Gating of}
RAM Chip Enable Signals
n _{SO-8 and S16 Packages}
n _{2.90V Precision Voltage Monitor}
n _{Power OK/Reset Time Delay: 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}
APPLICATIONS
n _{3.3V Low Power Systems}
n _{Critical μP Power Monitoring}
n _{Intelligent Instruments}
n _{Battery-Powered Computers and Controllers}
n _{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.
DESCRIPTION
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 pro-
tection, 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 V_CC 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
timeout period.
TYPICAL APPLICATION
V_IN ≥ 5V
+
51k
18k
LT1129-3.3
V_IN
V_OUT
3.3V
+
1μF
OUT SENSE ^100μF
V_CC
V_OUT
0.1μF _LTC695-3.3
SHDN
GND
V_BATT
2.4V
CE IN
CE OUT
RESET
PFO
PFI _GND WDI
MICROPROCESSOR RESET, BATTERY BACK-UP,
RAM WRITE PROTECTION, POWER WARNING AND
WATCHDOG TIMING ARE ALL IN A SINGLE CHIP
FOR 3.3V MICROPROCESSOR SYSTEM
0.1μF
POWER TO μP
CMOS RAM POWER
μP
SYSTEM
DECODER OUTPUT
RAM CS
μP RESET
μP NMI
I/O LINE
100Ω
0.1μF
694/5-3.3 TA01
RESET Output Voltage
vs Supply Voltage
5
4
3
2
1
0
0
1
2
3
4
5
SUPPLY VOLTAGE (V)
694/5-3.3 TA02
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