ISL12082IB8Z datasheet(9/26 Pages) INTERSIL

No de pièce	ISL12082IB8Z

Description	I2C-Bus??Real Time Clock with Two Interrupts, Alarm, and Timer

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Fabricant	INTERSIL [Intersil Corporation]

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9

FN6731.3

November 24, 2008

decoupling 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 ISL12082 for up to 10 years. Another option is to use a

Supercapacitor for applications where VDD is interrupted for

up to a month. See the “Application Section” on page 22 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 ISL12082 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 9

and 10.

The I2C bus is deactivated in battery backup mode to provide

lower power. Aside from this, all RTC functions are operational

during battery backup mode. Except for SCL and SDA, all the

inputs and outputs of the ISL12082 are active during battery

backup mode unless disabled via the control register.

Power Failure Detection

The ISL12082 provides a Real Time Clock Failure Bit (RTCF,

address 0Bh) 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 VDD and VBAT).

Low Power Mode

The normal power switching of the ISL12082 is designed to

switch into battery backup mode only if the VDD power is

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. Another mode, called Low

Power Mode, is available to allow direct switching from VDD

to VBAT without requiring VDD to drop below VTRIP. Since

the additional monitoring of VDD vs VTRIP is no longer

needed, that circuitry is shut down and less power is used

while operating from VDD. Power savings are typically

600nA at VDD = 5V. Low Power Mode is activated via the

LPMODE bit in the control and status registers.

Low Power Mode is useful in systems where VDD is normally

higher than VBAT at all times. The device will switch from

VDD to VBAT when VDD drops below VBAT, with about 50mV

of hysteresis to prevent any switchback of VDD after

switchover. In a system with a VDD = 5V and backup lithium

battery of VBAT = 3V, Low Power Mode can be used.

However, it is not recommended to use Low Power Mode in

a system with VDD = 3.3V ±10%, VBAT ≥ 3.0V, and when

there is a finite I-R voltage drop in the VDD line.

InterSeal™ and ReSeal™ Battery Saver

The ISL12082 has the InterSeal™ Battery Saver, which

prevents initial battery current drain before it is first used. For

example, battery-backed RTCs are commonly packaged on

a board with a battery connected. In order to preserve

battery life, the ISL12082 will not draw any power from the

battery source until after the device is first powered up from

the VDD source. Thereafter, the device will switchover to

battery backup mode whenever VDD power is lost.

VBAT - VBATHYS

VBAT

VBAT + VBATHYS

BATTERY BACKUP

MODE

VDD

VTRIP

2.2V

1.8V

FIGURE 9. BATTERY SWITCHOVER WHEN VBAT < VTRIP

FIGURE 10. BATTERY SWITCHOVER WHEN VBAT > VTRIP

VTRIP

VBAT

VTRIP + VTRIPHYS

BATTERY BACKUP

MODE

VDD

VTRIP

3.0V

2.2V

ISL12082

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