Voltage monitor input
Low Voltage Detect Output
V2 Voltage Fail Output
Serial Clock (SCL)
The SCL input is used to clock all data into and out of
Serial Data (SDA)
SDA is a bidirectional pin used to transfer data into
and out of the device. It is an open drain output and
may be wire-ORed with other open drain or open col-
lector outputs. An open drain requires the use of a
Write Protect (WP)
The WP pin should be tied HIGH at all time. (This WP
pin is reserved for internal factory testing only).
Reset Output (RESET)
RESET is an active LOW, open drain output which
goes active whenever VCC falls below the minimum
Vtrip sense level. It will remain active until VCC rises
above the minimum Vtrip sense level for 150ms.
RESET goes active if the Watchdog Timer is enabled
and there is no start bit before the end of the select-
able Watchdog time-out period. A serial start bit will
reset the Watchdog Timer. RESET also goes active on
power up at 1V and remains active for 150ms after the
power supply stabilizes.
V2 Voltage Fail Output (V2FAIL)
V2FAIL is an active LOW, open drain output which
goes active whenever V2MON falls below the mini-
mum V2trip sense level. It will remain active until
V2MON rises above the minimum V2MON sense level.
Power On Reset
Application of power to the X40620 activates a Power
On Reset Circuit. This circuit goes active at 1V and
pulls the RESET pin active. This signal prevents the
system microprocessor from starting to operate with
insufﬁcient voltage or prior to stabilization of the oscil-
lator. When VCC exceeds the device VTRIP value for
200ms (nominal) the circuit releases RESET allowing
the processor to begin executing code.
Low Voltage VCC (V1) Monitoring
During operation, the X40620 monitors the VCC level
and asserts RESET if supply voltage falls below a pre-
set minimum VTRIP. The RESET signal prevents the
microprocessor from operating in a power fail or
brownout condition. The RESET signal remains active
until the voltage drops below 1V. It also remains active
until VCC returns and exceeds VTRIP for 200ms.
When the internal low voltage detect circuitry senses
that VCC is low, the following happens:
– The RESET pin goes active.
– Communication to the device is interrupted and any
command is aborted. If a serial nonvolatile store is in
progress when power fails, the circuitry does not
stop the nonvolatile store operation, but attempts to
complete the operation.
The low VCC threshold is typically set to 3.1V for a 2.5
to 3.7V operating range.
LOW VOLTAGE V2 MONITORING
The X40620 also monitors a second voltage level and
asserts V2FAIL if the voltage falls below a preset mini-
mum V2TRIP. The V2FAIL signal is either ORed with
RESET to prevent the microprocessor from operating
in a power fail or brownout condition or used to inter-
rupt the microprocessor with notiﬁcation of an impend-
ing power failure. The V2FAIL signal remains active
until the VCC drops below 1V. It also remains active
until V2MON returns and exceeds V2TRIP by 0.2V
Characteristics subject to change without notice. 2 of 17