X40420/X40421 – Preliminary
Low VCC detection circuitry protects the user’s system
from low voltage conditions, resetting the system when
VCC falls below the minimum VTRIP1 point. RESET/
RESET is active until VCC returns to proper operating
level and stabilizes. A second voltage monitor circuit
tracks the unregulated supply to provide a power fail
warning or monitors different power supply voltage.
Three common low voltage combinations are available,
however, Xicor’s unique circuits allows the threshold for
either voltage monitor to be reprogrammed to meet
special needs or to ﬁne-tune the threshold for applica-
tions requiring higher precision.
A manual reset input provides debounce circuitry for
minimum reset component count.
A battery switch circuit compares VCC with VBATT input
and connects VOUT to whichever is higher. This pro-
vides voltage to external SRAM or other circuits in the
event of main power failure. The X40420/21 can drive
50mA from VCC to 250µA from VBATT. The device only
switches to VBATT when VCC drops below the low VCC
voltage threshold and VBATT.
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 WDO signal. The
user selects the interval from three preset values. Once
selected, the interval does not change, even after
cycling the power.
The memory portion of the device is a CMOS Serial
EEPROM array with Xicor’s Block Lock protection. The
array is internally organized as x 8. The device features
an 2-wire interface and software protocol allowing
operation on a two-wire bus.
The device utilizes Xicor’s proprietary Direct Write™
cell, providing a minimum endurance of 100,000 cycles
and a minimum data retention of 100 years.
14-Pin SOIC, TSSOP
14-Pin SOIC, TSSOP
1 V2FAIL V2 Voltage Fail Output. This open drain output goes LOW when V2MON is less than VTRIP2 and
goes HIGH when V2MON exceeds VTRIP2. There is no power up reset delay circuitry on this pin.
2 V2MON V2 Voltage Monitor Input. When the V2MON input is less than the VTRIP2 voltage, V2FAIL goes
LOW. This input can monitor an unregulated power supply with an external resistor divider or can
monitor a second power supply with no external components. Connect V2MON to VSS or VCC
when not used.
3 LOWLINE Early Low VCC Detect. This open drain output signal goes LOW when VCC < VTRIP1.
When VCC > VTRIP1, this pin is pulled high with the use of an external pull up resistor.
REV 1.2.14 7/12/02
Characteristics subject to change without notice. 2 of 25