ISL1219 Datasheet, PDF (9/24 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM and Event Detection

ISL1219
V_DD
V_BAT
V_TRIP
V_TRIP
BATTERY BACKUP
MODE
3.0V
2.2V
V_TRIP + V_TRIPHYS
FIGURE 12. BATTERY SWITCHOVER WHEN V_BAT > V_TRIP
The I²C bus is deactivated in battery backup mode to provide
lower power. Aside from this, all RTC functions are
operational during battery backup mode. Except for SCL and
SDA, all the inputs and outputs of the ISL1219 are active
during battery backup mode unless disabled via the control
register. The User SRAM is operational in battery backup
mode down to 1.8V.
Power Failure Detection
The ISL1219 provides a Real Time Clock Failure Bit (RTCF)
to detect total power failure. It allows users to determine if
the device has powered up after having lost all power to the
device (both V_DD and V_BAT).
Low Power Mode
The normal power switching of the ISL1219 is designed to
switch into battery backup mode only if the V_DD power is
lost. This will ensure that the device can accept a wide range
of backup voltages from many types of sources while reliably
switching into backup mode. Another mode, called Low
Power Mode, is available to allow direct switching from V_DD
to V_BAT without requiring V_DD to drop below V_TRIP. Since
the additional monitoring of V_DD vs. V_TRIP is no longer
needed, that circuitry is shut down and less power is used
while operating from V_DD. Power savings are typically
600nA at V_DD = 5V. Low Power Mode is activated via the
LPMODE bit in the control and status registers.
Low Power Mode is useful in systems where V_DD is normally
higher than V_BAT at all times. The device will switch from
V_DD to V_BAT when V_DD drops below V_BAT, with about 50mV
of hysteresis to prevent any switchback of V_DD after
switchover. In a system with a V_DD = 5V and backup lithium
battery of V_BAT = 3V, Low Power Mode can be used.
However, it is not recommended to use Low Power Mode in
a system with V_DD = 3.3V ±10%, V_BAT ≥ 3.0V, and when
there is a finite I-R voltage drop in the V_DD line.
InterSeal™ Battery Saver
The ISL1219 has the InterSeal™ Battery Saver which
prevents initial battery current drain before it is first used. For
example, battery-backed RTCs are commonly packaged on
a board with a battery connected. In order to preserve
battery life, the ISL1219 will not draw any power from the
battery source until after the device is first powered up from
the V_DD source. Thereafter, the device will switchover to
battery backup mode whenever V_DD power is lost.
Event/Tamper Monitor and Detection
The ISL1219 provides an event detection, time stamp and
alarm function to be used in a wide variety of applications
ranging from security, warranty monitoring, data collection
and recording.
The tamper detect input pin, EVIN, can be used as a event
or tamper detection input of an external switch (mechanical
or electronic). When the EVIN pin is a valid HIGH, the
ISL1219 sets the EVT bit in the status register and, can
optionally:
1. Issue an Event output signal (EVDET pin) and store time
stamp information in on board SRAM (second, minute,
hour, date, month and year)
2. At the time event occurred, stop the RTC registers from
advancing.
To allow for flexibility of external switches used at the EVIN
pin, the internal pull-up (~1µA in full on mode) can be
disabled/enabled. This will allow more flexibility depending
on the capacitive and resistive loading at the EVIN pin.
A noise filter option is also provided for the event monitor
circuit. The EVIN pin has a time based filter where the EVIN
signal must be stable for a period of time to trigger a valid
detection. The time hysteresis filter can vary from 0, 3.9ms,
15.2ms or 31.25ms.
For low power applications the event monitor can be
sampled at a user selectable rate. The EVIN pin can be
always ON or periodically sampled with a frequency of 1/4, 1
or 2Hz.
9
FN6314.2
July 15, 2010