ISL12022M 데이터 시트보기 (PDF) - Intersil

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ISL12022M

Real Time Clock with Embedded Crystal, ±5ppm Accuracy

Intersil 

ISL12022M

Pin Descriptions

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

supercapacitor or tied to ground if not used. See the Battery

Monitor parameter in the “DC Operating Characteristics-RTC”

table on page 3.

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 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 bi-directional pin used to transfer data into and out

of the device. It has an open drain output and may be OR’ed

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 VDD = 2.7V 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 ISL12022M

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 24 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 ISL12022M 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 12

and 13.

The I2C bus is deactivated in battery backup mode to reduce

power consumption. Aside from this, all RTC functions are

operational during battery backup mode. Except for SCL and

SDA, all the inputs and outputs of the ISL12022M are active

during battery backup mode unless disabled via the control

register.

VDD

BATTERY BACKUP

MODE

VTRIP

VBAT

2.2V

1.8V

VBAT - VBATHYS

VBAT + VBATHYS

FIGURE 12. BATTERY SWITCHOVER WHEN VBAT < VTRIP

VDD

VBAT

VTRIP

VTRIP

BATTERY BACKUP

MODE

3.0V

2.2V

VTRIP + VTRIPHYS

FIGURE 13. BATTERY SWITCHOVER WHEN VBAT > VTRIP

9

FN6668.5

July 10, 2009

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