ISL1218IUZ Ver la hoja de datos (PDF) - Renesas Electronics
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ISL1218IUZ Datasheet PDF : 21 Pages
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ISL1218
ISL1218 for up to 10 years. Another option is to use a Super
Cap for applications where VDD is interrupted for up to a
month. See the Applications Section for more information.
Normal Mode (VDD) to Battery Backup Mode (VBAT)
To transition from the VDD to VBAT mode, both of the following
conditions must be met:
Condition 1:
VDD < VBAT - VBATHYS
where VBATHYS 50mV
Condition 2:
VDD < VTRIP
where VTRIP 2.2V
Battery Backup Mode (VBAT) to Normal Mode (VDD)
The ISL1218 device will switch from the VBAT to VDD mode
when one of the following conditions occurs:
Condition 1:
VDD > VBAT + VBATHYS
where VBATHYS 50mV
Condition 2:
VDD > VTRIP + VTRIPHYS
where VTRIPHYS 30mV
These power control situations are illustrated in Figures 9 and
10.
VDD
VTRIP
VBAT
VBAT - VBATHYS
BATTERY BACKUP
MODE
2.2V
1.8V
VBAT + VBATHYS
FIGURE 9. BATTERY SWITCHOVER WHEN VBAT < VTRIP
VDD
VBAT
VTRIP
VTRIP
BATTERY BACKUP
MODE
3.0V
2.2V
VTRIP + VTRIPHYS
FIGURE 10. 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 ISL1218 are active during battery
backup mode unless disabled via the control register. The User
SRAM is operational in battery backup mode down to 2V.
Power Failure Detection
The ISL1218 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 ISL1218 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 ISL1218 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
ISL1218 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.
Real Time Clock Operation
The Real Time Clock (RTC) uses an external 32.768kHz
quartz crystal to maintain an accurate internal representation of
second, minute, hour, day of week, date, month, and year. The
RTC also has leap-year correction. The clock also corrects for
months having fewer than 31 days and has a bit that controls
24 hour or AM/PM format. When the ISL1218 powers up after
the loss of both VDD and VBAT, the clock will not begin
incrementing until at least one byte is written to the clock
register.
FN6313 Rev.0.00
Jun 22, 2006
Page 8 of 21
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