isl12020m Intersil Corporation, isl12020m Datasheet - Page 10

• Manufacturer Part Number: isl12020m
• Description: Real Time Clock With Embedded Crystal, ?5ppm Accuracy
• Manufacturer: Intersil Corporation

The I
power consumption. Aside from this, all RTC functions are
operational during battery-backup mode. Except for SCL and
SDA, all the inputs and outputs of the ISL12020M are active
during battery-backup mode unless disabled via the control
register.
The device Time Stamps the switchover from V
and V
registers respectively. If multiple V
occur before status is read, the earliest V
power-down time is stored and the most recent V
time is stored.
Temperature conversion and compensation can be enabled
in battery-backup mode. Bit BTSE in the BETA register
controls this operation, as described in “BETA Register
(BETA)” on page 18.
Power Failure Detection
The ISL12020M 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
Brownout Detection
The ISL12020M monitors the V
provides warning if the V
levels. There are six (6) levels that can be selected for the
trip level. These values are 85% below popular V
The LVDD bit in the Status Register will be set to “1” when
brownout is detected. Note that the I
active unless the Battery V
Battery Level Monitor
The ISL12020M has a built in warning feature once the Back
Up battery level drops first to 85% and then to 75% of the
battery’s nominal V
drops to between 85% and 75%, the LBAT85 bit is set in the
status register. When the level drops below 75%, both
LBAT85 and LBAT75 bits are set in the status register.
There is a Battery Time Stamp Function available. Once the
V
RTC time/date are written into the TSV2B register. This
information can be read from the TSV2B registers to
DD
FIGURE 13. BATTERY SWITCHOVER WHEN V
V
V
V
2
TRIP
is low enough to enable switchover to the battery, the
DD
BAT
BAT
C bus is deactivated in battery-backup mode to reduce
to V
V
TRIP
DD
, and the time is stored in t
BAT
BATTERY-BACKUP
level. When the battery voltage
DD
TRIP
DD
MODE
level drops below prescribed
10
and V
DD
levels are reached.
DD
level continuously and
2
power-down sequences
BAT
C serial bus remains
DD
).
V
TRIP
SV2B
to V
DD
BAT
+ V
BAT
BAT
and t
DD
TRIPHYS
to V
> V
3.0V
2.2V
to V
levels.
SB2V
BAT
TRIP
DD
ISL12020M
discover the point in time of the V
are multiple power-down cycles before reading these
registers, the first values stored in these registers will be
retained. These registers will hold the original power-down
value until they are cleared by setting CLRTS = 1 to clear the
registers.
The normal power switching of the ISL12022 is designed to
switch into battery-backup mode only if the V
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.
Note that the ISL12022 is not guaranteed to operate with
V
than this minimum, correct operation of the device,
especially after a V
Real Time Clock Operation
The Real Time Clock (RTC) uses an integrated 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
ISL12020M powers up after the loss of both V
the clock will not begin incrementing until at least one byte is
written to the clock register.
Single Event and Interrupt
The alarm mode is enabled via the MSB bit. Choosing Single
Event or interrupt alarm mode is selected via the IM bit. Note
that when the frequency output function is enabled, the
alarm function is disabled.
The standard alarm allows for alarms of time, date, day of
the week, month, and year. When a time alarm occurs in
single event mode, the IRQ/F
the alarm status bit (ALM) will be set to “1”.
The pulsed Interrupt mode allows for repetitive or recurring
alarm functionality. Hence, once the alarm is set, the device
will continue to alarm for each occurring match of the alarm
and present time. Thus, it will alarm as often as every minute
(if only the nth second is set) or as infrequently as once a
year (if at least the nth month is set). During pulsed Interrupt
mode, the IRQ/F
the alarm status bit (ALM) will be set to “1”.
The ALM bit can be reset by the user or cleared automatically
using the auto reset mode (see ARST bit). The alarm function
can be enabled/disabled during battery-backup mode using
the FOBATB bit. For more information on the alarm, please
see “ALARM Registers (10h to 15h)” on page 19.
Frequency Output Mode
The ISL12020M has the option to provide a clock output
signal using the IRQ/F
frequency output mode is set by using the FO bits to select
BAT
< 1.8V. If the battery voltage is expected to drop lower
OUT
DD
pin will be pulled low for 250ms and
OUT
power-down cycle, is not guaranteed.
open drain output pin. The
OUT
DD
pin will be pulled low and
power-down. If there
DD
DD
January 15, 2009
power is
and V
FN6667.2
BAT
,