REV 1.0 6/27/00
Characteristics subject to change without notice.
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Preliminary Information
ADVANCED INFORMATION
4K
X55020
Dual Voltage Monitor with Integrated System Battery Switch and EEPROM
FEATURES
Dual voltage monitoring
System battery switch-over circuitry
Early warning low V
CC
fail indicator
Active high and active low reset outputs
Selectable watchdog timer
--(0.15s, 0.4s, 0.8s, off)
Low V
CC
(V1MON) and V2MON detection and
reset assertion
--Four standard reset threshold voltages
--Re-program V1
TRIP
and V2
TRIP
reset threshold
voltage using special programming sequence
--Reset signal valid to V
CC
= 1V
Long battery life with low power consumption
--<50A max standby current, watchdog on
--<30A max standby current, watchdog off
--<1.5mA max active current during read
4Kbits of EEPROM
Built-in inadvertent write protection
--Power-up/power-down protection circuitry
--In circuit programmable ROM mode
10MHz SPI interface modes (0,0 & 1,1)
Minimize EEPROM programming time
--64-byte page write mode
--Self-timed write cycle
--5ms write cycle time (typical)
2.7V to 5.5V power supply operation
Available packages
--20-lead TSSOP
DESCRIPTION
This device combines power-on reset control, battery
switch circuit, watchdog timer, supply voltage supervi-
sion, secondary voltage supervision, and 4Kbit serial
EEPROM in one package. This combination lowers
system cost, reduces board space requirements, and
increases reliability.
Applying power to the device activates the power on
reset circuit which holds RESET/RESET active for a
period of time. This allows the power supply and oscilla-
tor to stabilize before the processor can execute code.
A system battery switch circuit compares V
CC
(V1MON) with V
BATT
input and connects V
OUT
to
whichever is higher. This provides voltage to external
SRAM or other circuits in the event of main power fail-
ure. The X55020 can drive 50mA from V
CC
and 250A
from V
BATT
. The device switches to V
BATT
when V
CC
drops below the low V
CC
voltage threshold and V
BATT
.
The Watchdog Timer provides an independent protec-
tion mechanism for microcontrollers. When the micro-
controller fails to restart a timer within a selectable
time-out interval, the device activates the RESET/
RESET signal. The user selects the interval from three
preset values. Once selected, the interval does not
change, even after cycling the power.
The device's low V
CC
detection circuitry protects the
user's system from low voltage conditions, resetting the
system when V
CC
(V1MON) falls below the minimum
V
CC
trip point (V1
TRIP
). RESET/RESET is asserted
until V
CC
returns to proper operating level and stabi-
lizes. A second voltage monitor circuit tracks the unreg-
ulated supply or monitors a second power supply
voltage to provide a power fail warning. Xicor's unique
circuits allow the threshold for either voltage monitor to
be reprogrammed to meet special needs or to fine-tune
the threshold for applications requiring higher precision.
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