ISL1218 データシートの表示（PDF） - Renesas Electronics

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ISL1218

Low Power RTC with Battery Backed SRAM

Renesas Electronics 

ISL1218

EQUIVALENT AC OUTPUT LOAD CIRCUIT FOR VDD = 5V

5.0V

SDA

AND

IRQ/FOUT

1533

FOR VOL= 0.4V

AND IOL = 3mA

100pF

FIGURE 7. STANDARD OUTPUT LOAD FOR TESTING THE

DEVICE WITH VDD = 5.0V

General Description

The ISL1218 device is a low power real time clock with timing

and crystal compensation, clock/calendar, power fail indicator,

periodic or polled alarm, intelligent battery backup switching,

and battery-backed user SRAM.

The oscillator uses an external, low-cost 32.768kHz crystal.

The real time clock tracks time with separate registers for

hours, minutes, and seconds. The device has calendar

registers for date, month, year and day of the week. The

calendar is accurate through 2099, with automatic leap year

correction.

The ISL1218's powerful alarm can be set to any clock/calendar

value for a match. For example, every minute, every Tuesday

or at 5:23 AM on March 21. The alarm status is available by

checking the Status Register, or the device can be configured

to provide a hardware interrupt via the IRQ pin. There is a

repeat mode for the alarm allowing a periodic interrupt every

minute, every hour, every day, etc.

The device also offers a backup power input pin. This VBAT pin

allows the device to be backed up by battery or SuperCap with

automatic switchover from VDD to VBAT. The entire ISL1218

device is fully operational from 2.0V to 5.5V and the

clock/calendar portion of the device remains fully operational

down to 1.8V (Standby Mode).

Pin Description

X1, X2

The X1 and X2 pins are the input and output, respectively, of

an inverting amplifier. An external 32.768kHz quartz crystal is

used with the ISL1218 to supply a timebase for the real time

clock. Internal compensation circuitry provides high accuracy

over the operating temperature range from -40°C to +85°C.

This oscillator compensation network can be used to calibrate

the crystal timing accuracy over temperature either during

manufacturing or with an external temperature sensor and

microcontroller for active compensation. The device can also

be driven directly from a 32.768kHz source at pin X1.

X1

X2

FIGURE 8. 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.

IRQ/FOUT (Interrupt Output/Frequency Output)

This dual function pin can be used as an interrupt or frequency

output pin. The IRQ/FOUT mode is selected via the frequency

out control bits of the control/status register.

• 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.

• Frequency Output Mode. The 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.

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 2.0V 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

FN6313 Rev.0.00

Jun 22, 2006

Page 7 of 21

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