FN6667 datasheet(11/34 Pages) RENESAS

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ISL12020M

FN6667 Rev 6.00

Page 11 of 34

January 9, 2015

General Description

The ISL12020M device is a low power Real Time Clock (RTC) with

embedded temperature sensor and crystal. It contains crystal

frequency compensation circuitry over the temperature range of

0°C to 85°C good to ±5ppm accuracy. It also contains a

clock/calendar with Daylight Savings Time (DST) adjustment,

power fail and low battery monitors, brownout indicator, 1 periodic

or polled alarm, intelligent battery-backup switching and 128

Bytes of battery-backed user SRAM.

The oscillator uses an internal 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. In addition, both the

ISL12020M could be programmed for automatic Daylight

Savings Time (DST) adjustment by entering local DST

information.

The ISL12020M’s 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/FOUT 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 Super Capacitor

with automatic switchover from VDD to VBAT. The ISL12020M

device is specified for VDD = 2.7V to 5.5V and the clock/calendar

portion of the device remains fully operational in battery-backup

mode down to 1.8V (Standby Mode). The VBAT level is monitored

and reported against preselected levels. The first report is

registered when the VBAT level falls below 85% of nominal level,

the second level is set for 75%. Battery levels are stored in

PWR_VBAT registers.

The ISL12020M offers a “Brownout” alarm once the VDD falls

below a preselected trip level. This allows system Micro to save

vital information to memory before complete power loss. There

are six VDD levels that could be selected for initiation of the

Brownout alarm.

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 ISL12020M for up

to 10 years. Another option is to use a Super Capacitor for

applications where VDD is interrupted for up to a month. See the

“Application Section” on page 28 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 ISL12020M 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 13 and

14.

FIGURE 11. IDD with TSE = 1 vs TEMPERATURE

FIGURE 12. OSCILLATOR CHANGE vs TEMPERATURE AT DIFFERENT

AGING SETTINGS (IATR) (BETA SET FOR 1ppm STEPS)

Typical Performance Curves Temperature is +25°C unless otherwise specified. (Continued)

100

110

-40

-20

204060

TEMPERATURE (°C)

VBAT = 2.7V

VDD = 3.3V

VDD = 5.5V

-80

-60

-40

-20

-40

-20

406080

TEMPERATURE (°C)

62.5ppm

32ppm

0ppm

-31ppm

-61.5ppm

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