ISL1221 データシートの表示（PDF） - Renesas Electronics
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ISL1221 Datasheet PDF : 24 Pages
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ISL1221
VDD
VTRIP
VBAT
VBAT - VBATHYS
BATTERY BACKUP
MODE
2.2V
1.8V
VBAT + VBATHYS
FIGURE 11. BATTERY SWITCHOVER WHEN VBAT < VTRIP
VDD
VBAT
VTRIP
VTRIP
BATTERY BACKUP
MODE
3.0V
2.2V
VTRIP + VTRIPHYS
FIGURE 12. BATTERY SWITCHOVER WHEN VBAT > VTRIP
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 ISL1221 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 ISL1221 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 VDD and VBAT).
Low Power Mode
The normal power switching of the ISL1221 is designed to
switch into battery backup mode only if the VDD 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 VDD to VBAT
without requiring VDD to drop below VTRIP. Since the
additional monitoring of VDD vs. VTRIP is no longer needed,
that circuitry is shut down and less power is used while
operating from VDD. Power savings are typically 600nA at VDD
= 5V. Low Power Mode is activated via the LPMODE bit in the
control and status registers.
Low Power Mode is useful in systems where VDD is normally
higher than VBAT at all times. The device will switch from VDD
to VBAT when VDD drops below VBAT, with about 50mV of
hysteresis to prevent any switchback of VDD after switchover.
In a system with a VDD = 5V and backup lithium battery of
VBAT = 3V, Low Power Mode can be used. However, it is not
recommended to use Low Power Mode in a system with VDD =
3.3V ±10%, VBAT 3.0V, and when there is a finite I-R voltage
drop in the VDD line.
InterSeal™ Battery Saver
The ISL1221 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
ISL1221 will not draw any power from the battery source until
after the device is first powered up from the VDD source.
Thereafter, the device will switchover to battery backup mode
whenever VDD power is lost.
Event/Tamper Monitor and Detection
The ISL1221 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 ISL1221
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.
FN6316 Rev 1.00
July 15, 2010
Page 9 of 24
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