X40020 Datasheet, PDF (3/24 Pages) Intersil Corporation – Dual Voltage Monitor with Intergrated CPU Supervisor and System Battery Switch

X40020, 40021
PIN DESCRIPTION (Continued)
Pin Name
Function
7
V_SS
Ground
8
SDA Serial Data. SDA is a bidirectional pin used to transfer data into and out of the device. It has an open
drain output and may be wire ORed with other open drain or open collector outputs. This pin requires
a pull up resistor and the input buffer is always active (not gated).
Watchdog Input. A HIGH to LOW transition on the SDA (while SCL is toggled from HIGH to LOW
and followed by a stop condition) restarts the Watchdog timer. The absence of this transition within
the watchdog time out period results in WDO going active.
9
SCL
Serial Clock. The Serial Clock controls the serial bus timing for data input and output.
10
WP
Write Protect. WP HIGH prevents writes to any location in the device (including all the registers). It
has an internal pull down resistor. (>10MΩ typical)
11
V_BATT Battery Supply Voltage. This input provides a backup supply in the event of a failure of the
primary V_CC voltage. The V_BATT voltage typically provides the supply voltage necessary to
maintain the contents of SRAM and also powers the internal logic to “stay awake.” If the battery is not
used, connect V_BATT to ground.
12
V_OUT
Output Voltage. (V)
V_OUT = V_CC if V_CC > V_TRIP1.
IF V_CC < V_TRIP1
then V_OUT = V_CC if V_CC > V_BATT + 0.03V
else V_OUT = V_BATT (ie if V_CC < V_BATT – 0.03V)
Note: There is hysteresis around V_BATT ± 0.03V point to avoid oscillation at or near the
switchover voltage. A capacitance of 0.1µF must be connected to V_OUT to ensure stability.
13 BATT-ON Battery On. This CMOS output goes HIGH when the V_OUT switches to V_BATT and goes LOW when
V_OUT switches to V_CC. It is used to drive an external PNP pass transistor when V_CC = V_OUT and current
requirements are greater than 50mA.
The purpose of this output is to drive an external transistor to get higher operating currents when the
V_CC supply is fully functional. In the event of a V_CC failure, the battery voltage is applied to the V_OUT
pin and the external transistor is turned off. In this “backup condition,” the battery only needs to supply
enough voltage and current to keep SRAM devices from losing their data–there is no communication
at this time.
14
V_CC
Supply Voltage
3
FN8112.0
March 28, 2005