ISL1221 Ver la hoja de datos (PDF) - Renesas Electronics
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ISL1221 Datasheet PDF : 24 Pages
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ISL1221
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FIGURE 10. RECOMMENDED CRYSTAL CONNECTION
VBAT
This input provides a backup supply voltage to the device.
VBAT supplies power to the device in the event that the VDD
supply fails. This pin can be connected to a battery, a Super
Cap or tied to ground if not used.
EVIN (Event Input)
The EVIN pin is an input that is used to detect an externally
monitored event. When a high signal is present at the EVIN
pin, an “event” is detected. This input may be used for various
monitoring functions, such as the opening of a detection switch
on a chassis or door. The event detection circuit can be user
enabled or disabled (see EVEN bit) and provides the option to
be operational in battery backup modes (see EVBATB bit).
When the event detection is disabled the EVIN pin is gated
OFF. See“Functional Description” on page 8 for more details.
FOUT (Frequency Output)
The FOUT pin outputs a clock signal which is related to the
crystal frequency. The frequency output is user selectable and
enabled via the I2C bus. It is an open drain active low output.
When not used, the output is high.
IRQ/EVDET (Alarm/Event Detect Output)
This dual function pin can be used as an interrupt alarm or
event detect output pin. Checking the status register will show
the type of interrupt, Alarm or Event Detect.
• Interrupt Mode. The pin provides an interrupt signal output.
This signal notifies a host processor that an alarm has
occurred and requests action. It is an open drain active low
output.
• The output will go low when an event is detected at the EVIN
pin. If the event detection function is enabled, the
IRQ/EVDET output will go low and stay low until the EVT bit
is cleared (see the EVIN pin description in the “Pin
Description” on page 7).
Serial Clock (SCL)
The SCL input is used to clock all serial data into and out of the
device. The input buffer on this pin is always active (not gated).
It is disabled when the backup power supply on the VBAT pin is
activated to minimize power consumption.
Serial Data (SDA)
SDA is a bidirectional pin used to transfer data into and out of
the device. It has an open drain output and may be ORed with
other open drain or open collector outputs. The input buffer is
always active (not gated) in normal mode.
An open drain output requires the use of a pull-up resistor. The
output circuitry controls the fall time of the output signal with
the use of a slope controlled pull-down. The circuit is designed
for 400kHz I2C interface speeds. It is disabled when the
backup power supply on the VBAT pin is activated.
VDD, GND
Chip power supply and ground pins. The device will operate
with a power supply from VDD=2.7V to 5.5VDC. A 0.1µF
capacitor is recommended on the VDD pin to ground.
Functional Description
Power Control Operation
The power control circuit accepts a VDD and a VBAT input.
Many types of batteries can be used with Intersil RTC
products. For example, 3.0V or 3.6V Lithium batteries are
appropriate, and battery sizes are available that can power the
ISL1221 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 “Application Section” on page 20 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 ISL1221 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 11 and
12.
FN6316 Rev 1.00
July 15, 2010
Page 8 of 24
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