ISL12024IRTCZ Datasheet, PDF(22/24 Page) Intersil Corporation – Real-Time Clock/Calendar with Embedded Unique ID

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ISL12024IRTCZ Datasheet, PDF (22/24 Pages) Intersil Corporation – Real-Time Clock/Calendar with Embedded Unique ID

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ISL12024IRTCZ

Backup Battery Operation

Many types of batteries can be used with the Intersil RTC

products. 3.0V or 3.6V Lithium batteries are appropriate, and

sizes are available that can power a Intersil RTC device for

up to 10 years. Another option is to use a super capacitor for

applications where VDD may disappear intermittently for

short periods of time. Depending on the value of

superconductor used, backup time can last from a few days

to two weeks (with >1F). A simple silicon or Schottky barrier

diode can be used in series with VDD to charge the

superconductor, which is connected to the VBAT pin. Try to

use Schottky diodes with very low leakages, <1ÂµA desirable.

Do not use the diode to charge a battery (especially lithium

batteries!)

There are two possible modes for battery backup operation;

Standard and Legacy Mode. In Standard Mode, there are no

operational concerns when switching over to battery backup

since all other devices functions are disabled. Battery drain

is minimal in Standard Mode, and return to Normal VDD

powered operations is predictable. In Legacy Mode, the

VBAT pin can power the chip if the voltage is above VDD and

less than VTRIP. In this mode, it is possible to generate alarm

and communicate with the device, unless SBI = 1, but the

supply current drain is much higher than the Standard Mode

and backup time is reduced. In this case if alarms are used

in backup mode, the IRQ/FOUT pull-up resistor must be

connected to VBAT voltage source. During initial power-up

the default mode is the Standard Mode.

2.7V TO 5.5V

VDD

VBAT

VSS

SUPERCAPACITOR

FIGURE 24. SUPERCAPACITOR CHARGING CIRCUIT

Alarm Operation Examples

Below are examples of both Single Event and periodic

Interrupt Mode alarms.

EXAMPLE 1

Alarm0 set with single interrupt (IM = â0â)

A single alarm will occur on January 1 at 11:30am.

A. Set Alarm0 registers as follows:

BIT

ALARM0

SCA0 0 0 0 0 0 0 0 0 00h Seconds disabled

MNA0 1 0 1 1 0 0 0 0 B0h Minutes set to 30,

enabled

BIT

ALARM0

HRA0 1 0 0 1 0 0 0 1 91h Hours set to 11,

enabled

DTA0

1 0 0 0 0 0 0 1 81h Date set to 1,

enabled

MOA0 1 0 0 0 0 0 0 1 81h Month set to 1,

enabled

DWA0 0 0 0 0 0 0 0 0 00h Day of week

disabled

B. Also, the AL0E bit must be set as follows:

BIT

CONTROL

INT

0 0 1 0 0 0 0 0 x0h Enable Alarm

After these registers are set, an alarm will be generated when

the RTC advances to exactly 11:30am on January 1 (after

seconds changes from 59 to 00) by setting the AL0 bit in the

status register to â1â and also bringing the IRQ/FOUT output

low.

EXAMPLE 2

Pulsed interrupt once per minute (IM = â1â)

Interrupts at one minute intervals when the seconds register

is at 30 seconds.

A. Set Alarm0 registers as follows:

BIT

ALARM0

DESCRIPTION

SCA0

1 0 1 1 0 0 0 0 B0h Seconds set to 30,

enabled

MNA0 0 0 0 0 0 0 0 0 00h Minutes disabled

HRA0 0 0 0 0 0 0 0 0 00h Hours disabled

DTA0 0 0 0 0 0 0 0 0 00h Date disabled

MOA0 0 0 0 0 0 0 0 0 00h Month disabled

DWA0 0 0 0 0 0 0 0 0 00h Day of week disabled

B. Set the Interrupt register as follows:

BIT

CONTROL

DESCRIPTION

INT 1 0 1 0 0 0 0 0 x0h Enable Alarm and Int

Mode

FN6749.0

August 8, 2008

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