ISL1219IUZ-T datasheet(9/24 Pages) INTERSIL

Numer części	ISL1219IUZ-T

Szczegółowy opis	Low Power RTC with Battery Backed SRAM and Event Detection

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Producent	INTERSIL [Intersil Corporation]

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9

FN6314.1

August 14, 2006

These power control situations are illustrated in Figures 11

and 12.

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 ISL1219 are active

during battery backup mode unless disabled via the control

register. The User SRAM is operational in battery backup

mode down to 1.8V.

Power Failure Detection

The ISL1219 provides a Real Time Clock Failure Bit (RTCF)

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 ISL1219 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™ Battery Saver

The ISL1219 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 ISL1219 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.

Event/Tamper Monitor and Detection

The ISL1219 provides an event detection, time stamp and

alarm function to be used in a wide variety of applications

ranging from security, warranty monitoring, data collection

and recording.

The tamper detect input pin, EVIN, can be used as a event

or tamper detection input of an external switch (mechanical

or electronic). When the EVIN pin is a valid HIGH, the

ISL1219 sets the EVT bit in the status register and, can

optionally: 1) Issue an Event output signal (EVDET pin) and

store time stamp information in on board SRAM (second,

minute, hour, date, month and year), 2) At the time event

occurred, stop the RTC registers from advancing.

To allow for flexibility of external switches used at the EVIN

pin, the internal pull-up (~1µA in full on mode) can be

disabled/enabled. This will allow more flexibility depending

on the capacitive and resistive loading at the EVIN pin.

A noise filter option is also provided for the event monitor

circuit. The EVIN pin has a time based filter where the EVIN

signal must be stable for a period of time to trigger a valid

detection. The time hysteresis filter can vary from 0, 3.9ms,

15.2ms or 31.25ms.

For low power applications the event monitor can be

sampled at a user selectable rate. The EVIN pin can be

always ON or periodically sampled with a frequency of 1/4, 1

or 2Hz.

VBAT - VBATHYS

VBAT

VBAT + VBATHYS

BATTERY BACKUP

MODE

VDD

VTRIP

2.2V

1.8V

FIGURE 11. BATTERY SWITCHOVER WHEN VBAT < VTRIP

FIGURE 12. BATTERY SWITCHOVER WHEN VBAT > VTRIP

VTRIP

VBAT

VTRIP + VTRIPHYS

BATTERY BACKUP

MODE

VDD

VTRIP

3.0V

2.2V

ISL1219

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