LTC1235_15 Datasheet, PDF (1/16 Pages) Linear Technology – Microprocessor Supervisory Circuit

LTC1235
Microprocessor
Supervisory Circuit
FEATURES
n _{Guaranteed Reset Assertion at VCC = 1V}
n _{1.5mA Maximum Supply Current}
n _{Fast (35ns Max.) Onboard Gating of RAM Chip}
Enable Signals
n _{Conditional Battery Backup Extends Battery Life}
n _{4.65V Precision Voltage Monitor}
n _{Power OK/Reset Time Delay: 200ms}
n _{External Reset Control}
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 _{All the LTC695 Features Plus Conditional Battery}
Backup and External Reset Control
APPLICATIONS
n _{Critical μP Power Monitoring}
n _{Intelligent Instruments}
n _{Battery-Powered Computers and Controllers}
n _{Automotive Systems}
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
DESCRIPTION
The LTC^®1235 provides complete power supply monitoring
and battery control functions for microprocessor reset,
battery backup, RAM write protection, power failure warn-
ing and watchdog timing. The LTC1235 has all the LTC695
features plus conditional battery backup and external reset
control. When an out-of-tolerance power supply condition
occurs, the reset outputs are forced to active states and
the Chip Enable output write-protects external memory.
The RESET output is guaranteed to remain logic low with
V_CC as low as 1V. External reset control is provided by a
debounced pushbutton reset input.
The LTC1235 powers the active CMOS 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, provides backup
power to the RAMs. The LTC1235 can be programmed by
a P signal to either back up the RAMs or not. This extends
the battery life in situations where RAM data need not
always be saved when power goes down.
For an early warning of impending power failure, the
LTC1235 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 the time-out
period.
TYPICAL APPLICATION
V_IN ≥ 7.5V
+
10μF
LT1086-5
V_IN
V_OUT
ADJ
+5V
+
100μF
51k
10k
V_CC
V_OUT
0.1μF
LTC1235
V_BATT BACKUP
+3V
RESET
PFO
PFI
PB RST
WDI
POWER TO μP
0.1μF ^{CMOS RAM POWER}
I/O LINE
μP RESET
μP NMI
I/O LINE
μP
SYSTEM
1235 TA1
THE LTC1235 EXTENDS BATTERY LIFE BY PROVIDING BATTERY POWER ONLY WHEN REQUIRED TO BACK UP RAM DATA.
IT SAVES THE BATTERY WHEN NO DATA BACKUP IS NEEDED. THE μP REQUESTS BACKUP WITH THE BACKUP PIN.
Battery Life vs
Backup Duty Cycle
10
9
LTC1235
8
7
6
5
LTC695
4
(WITHOUT
CONDITIONAL
3
BATTERY
BACKUP)
2
1
0
0
20
40
60
80 100
BACKUP DUTY CYCLE (%)
1235 TA02
1235fa
1