X45620 Datasheet, PDF (11/20 Pages) Intersil Corporation – Dual Voltage Monitor with Integrated System Battery Switch and EEPROM

X45620
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 hystere-
sis 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 external pass ele-
ments to provide additional current to the external cir-
cuits 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.
Manual Reset
By connecting a push-button from MR to ground or
driven by logic, the designer adds manual system reset
capability. The RESET pins is asserted when the push-
button is closed and remain asserted for t_PURST after the
push-button is released. This pin is debounced so a
push-button connected directly to the device will have
both clean falling and rising edges on MR.
Figure 2. Example System Connection
Unregulated
5V
Supply
Reg
Dual P-channel FET
Examples: IRF 7756, FDS9733A
V2MON
Provides
Early Detection
of Power Failure
+
Supercap
V_{CC BATT-ON}
V_OUT
V_BATT
V2MON
V2FAIL
RESET
SDA, SCL
V_SS
SRAM
Address
Decode
Enable
NMI
Addr
V_CC
RESET
2-Wire ^µC
11
FN8250.0
July 29, 2005