X55060 Datasheet, PDF (5/23 Pages) Intersil Corporation – Dual Voltage Monitor with Integrated System Battery Switch and EEPROM

X55060
Figure 1. Two Uses of Dual Voltage Monitoring
Unregulated
Supply
5V
Reg
R1
R2 V2
V_OUT
X55060
V_CC
RESET
V2MON
V2FAIL
System
Reset
System
Interrupt
R1 and R2 selected so V2 = V2MON threshold when
Unregulated supply reaches 6V.
Unregulated
Supply
5V
Reg
3.3V
Reg
X55060
V_CC
RESET
V2MON
V2FAIL
V_OUT
System
Reset
Notice: No external components required to monitor
two voltages.
Watchdog Timer
The Watchdog Timer circuit monitors the microproces-
sor activity by monitoring the CS/WDI pin. The micro-
processor must toggle the CS/WDI pin HIGH to LOW
periodically prior to the expiration of the watchdog time
out period to prevent the WDO signal going active.
The state of two nonvolatile control bits in the Status
Register determines the watchdog timer period. The
microprocessor can change these watchdog bits by
writing to the status register. The factory default set-
ting disables the watchdog timer.
The Watchdog Timer oscillator stops when in battery
backup mode. It re-starts when V_CC returns.
System Battery Switch
As long as V_CC exceeds the low voltage detect thresh-
old V_TRIP1, V_OUT is connected to V_CC through a 5Ω
(typical) switch. When the V_CC has fallen below V_TRIP,
then V_CC is applied to V_OUT if V_CC is equal to or
greater than V_BATT + 0.03V. When V_CC drops to less
than V_BATT - 0.03V, then V_OUT is connected to V_BATT
through an 80Ω (typical) switch. V_OUT typically sup-
plies the system static RAM voltage, so the switchover
circuit operates to protect the contents of the static
RAM during a power failure. Typically, when V_CC has
failed, the SRAMs go into a lower power state and
draw much less current than in their active mode.
When V_CC returns, V_OUT switches back to V_CC when
V_CC exceeds V_BATT + 0.03V. There is a 60mV hyster-
esis around this battery switch threshold to prevent
oscillations between supplies.
While V_CC is connected to V_OUT the BATT-ON pin is
pulled LOW. The signal can drive an external PNP
transistor to provide additional current to the external
circuits during normal operation.
Operation
The device is in normal operation with V_CC as long as
V_CC > V_TRIP1. It switches to the battery backup mode
when V_CC goes away.
Condition
V_CC > V_TRIP1
V_CC > V_TRIP1 &
V_BATT = 0
0 ≤ V_CC V_TRIP1
and V_CC < V_BATT
Mode of Operation
Normal Operation.
Normal Operation without battery
back up capability.
Battery Backup Mode; RESET
signal is asserted. No communica-
tion to the device is allowed.
5
FN8133.0
March 28, 2005