X1227S8I-2.7A Datasheet X1227S8, X1227S8-2.7, X1227S8-2.7A | P22-P24

FN8099.2

May 8, 2006

Random Read

Random read operations allows the master to access

any location in the X1227. Prior to issuing the Slave

Address Byte with the R/W

bit set to zero, the master

must first perform a “dummy” write operation.

The master issues the start condition and the slave

address byte, receives an acknowledge, then issues

the word address bytes. After acknowledging receipt

of each word address byte, the master immediately

issues another start condition and the slave address

byte with the R/W

bit set to one. This is followed by an

acknowledge from the device and then by the eight bit

data word. The master terminates the read operation

by not responding with an acknowledge and then issu-

ing a stop condition. Refer to Figure 17 for the

address, acknowledge, and data transfer sequence.

In a similar operation called “Set Current Address,” the

device sets the address if a stop is issued instead of

the second start shown in Figure 17. The X1227 then

goes into standby mode after the stop and all bus

activity will be ignored until a start is detected. This

operation loads the new address into the address

counter. The next Current Address Read operation will

read from the newly loaded address. This operation

could be useful if the master knows the next address it

needs to read, but is not ready for the data.

Sequential Read

Sequential reads can be initiated as either a current

address read or random address read. The first data

byte is transmitted as with the other modes; however,

the master now responds with an acknowledge, indi-

cating it requires additional data. The device continues

to output data for each acknowledge received. The

master terminates the read operation by not responding

with an acknowledge and then issuing a stop condition.

The data output is sequential, with the data from

address n followed by the data from address n + 1.

The address counter for read operations increments

through all page and column addresses, allowing the

entire memory contents to be serially read during one

operation. At the end of the address space the counter

“rolls over” to the start of the address space and the

X1227 continues to output data for each acknowledge

received. Refer to Figure 18 for the acknowledge and

data transfer sequence.

Figure 17. Random Address Read Sequence

Figure 18. Sequential Read Sequence

Slave

Address

Word

Address 1

Slave

Address

Data

SDA Bus

Signals from

the Slave

Signals from

the Master

Word

Address 0

1111

0000000

Data

(2)

Slave

Address

Data

(n)

SDA Bus

Signals from

the Slave

Signals from

the Master

Data

(n-1)

(n is any integer greater than 1)

Data

(1)

X1227

FN8099.2

May 8, 2006

APPLICATION SECTION

CRYSTAL OSCILLATOR AND TEMPERATURE

COMPENSATION

Intersil has now integrated the oscillator compensation

circuity on-chip, to eliminate the need for external

components and adjust for crystal drift over tempera-

ture and enable very high accuracy time keeping

(<5ppm drift.

The Intersil RTC family uses an oscillator circuit with

on-chip crystal compensation network, including

adjustable load-capacitance. The only external com-

ponent required is the crystal. The compensation net-

work is optimized for operation with certain crystal

parameters which are common in many of the surface

mount or tuning-fork crystals available today. Table 6

summarizes these parameters.

Table 7 contains some crystal manufacturers and part

numbers that meet the requirements for the Intersil

RTC products.

The turnover temperature in Table 6 describes the

temperature where the apex of the of the drift vs. tem-

perature curve occurs. This curve is parabolic with the

drift increasing as (T-T0)

. For an Epson MC-405

device, for example, the turnover temperature is typi-

cally 25 deg C, and a peak drift of >110ppm occurs at

the temperature extremes of -40 and +85 deg C. It is

possible to address this variable drift by adjusting the

load capacitance of the crystal, which will result in pre-

dictable change to the crystal frequency. The Intersil

RTC family allows this adjustment over temperature

since the devices include on-chip load capacitor trim-

ming. This control is handled by the Analog Trimming

capacitance range covered by the ATR circuit is

approximately 3.25pF to 18.75pF, in 0.25pf incre-

ments. Note that actual capacitance would also

include about 2pF of package related capacitance. In-

circuit tests with commercially available crystals dem-

onstrate that this range of capacitance allows fre-

quency control from +116ppm to -37ppm, using a

12.5pF load crystal.

In addition to the analog compensation afforded by the

adjustable load capacitance, a digital compensation

feature is available for the Intersil RTC family. There

are three bits known as the Digital Trimming Register

or DTR, and they operate by adding or skipping pulses

in the clock signal. The range provided is ±30ppm in

increments of 10ppm. The default setting is 0ppm. The

DTR control can be used for coarse adjustments of

frequency drift over temperature or for crystal initial

accuracy correction.

Table 6. Crystal Parameters Required for Intersil RTC’s

Table 7. Crystal Manufacturers

Parameter Min Typ Max Units Notes

Frequency 32.768 kHz

Freq. Tolerance ±100 ppm Down to 20ppm if desired

Turnover Temperature 20 25 30 °C Typically the value used for most

crystals

Operating Temperature Range -40 85 °C

Parallel Load Capacitance 12.5 pF

Equivalent Series Resistance 50 kΩ For best oscillator performance

Manufacturer Part Number Temp Range +25°C Freq Toler.

Citizen CM201, CM202, CM200S -40 to +85°C ±20ppm

Epson MC-405, MC-406 -40 to +85°C ±20ppm

Raltron RSM-200S-A or B -40 to +85°C ±20ppm

SaRonix 32S12A or B -40 to +85°C ±20ppm

Ecliptek ECPSM29T-32.768K -10 to +60°C ±20ppm

ECS ECX-306/ECX-306I -10 to +60°C ±20ppm

Fox FSM-327 -40 to +85°C ±20ppm

X1227

FN8099.2

May 8, 2006

A final application for the ATR control is in-circuit cali-

bration for high accuracy applications, along with a

temperature sensor chip. Once the RTC circuit is pow-

ered up with battery backup, the frequency drift is

measured. The ATR control is then adjusted to a set-

ting which minimizes drift. Once adjusted at a particu-

lar temperature, it is possible to adjust at other

discrete temperatures for minimal overall drift, and

store the resulting settings in the EEPROM. Extremely

low overall temperature drift is possible with this

method. The Intersil evaluation board contains the cir-

cuitry necessary to implement this control.

For more detailed operation see Intersil’s application

note AN154 on Intersil’s website at www.intersil.com.

Layout Considerations

The crystal input at X1 has a very high impedance and

will pick up high frequency signals from other circuits on

the board. Since the X2 pin is tied to the other side of

the crystal, it is also a sensitive node. These signals can

couple into the oscillator circuit and produce double

clocking or mis-clocking, seriously affecting the accu-

racy of the RTC. Care needs to be taken in layout of the

RTC circuit to avoid noise pickup. Below in Figure 19 is

a suggested layout for the X1226 or X1227 devices.

Figure 19. Suggested Layout for Intersil RTC in SO-8

The X1 and X2 connections to the crystal are to be

kept as short as possible. A thick ground trace around

the crystal is advised to minimize noise intrusion, but

ground near the X1 and X2 pins should be avoided as

it will add to the load capacitance at those pins. Keep

in mind these guidelines for other PCB layers in the

vicinity of the RTC device. A small decoupling capaci-

tor at the Vcc pin of the chip is mandatory, with a solid

connection to ground.

For other RTC products, the same rules stated above

should be observed, but adjusted slightly since the

packages and pinouts are slightly different.

Assembly

Most electronic circuits do not have to deal with

assembly issues, but with the RTC devices assembly

includes insertion or soldering of a live battery into an

unpowered circuit. If a socket is soldered to the board,

and a battery is inserted in final assembly, then there

are no issues with operation of the RTC. If the battery

is soldered to the board directly, then the RTC device

Vback pin will see some transient upset from either

soldering tools or intermittent battery connections

which can stop the circuit from oscillating. Once the

battery is soldered to the board, the only way to assure

the circuit will start up is to momentarily (very short

period of time!) short the Vback pin to ground and the

circuit will begin to oscillate.

Oscillator Measurements

When a proper crystal is selected and the layout guide-

lines above are observed, the oscillator should start up

in most circuits in less than one second. Some circuits

may take slightly longer, but startup should definitely

occur in less than 5 seconds. When testing RTC cir-

cuits, the most common impulse is to apply a scope

probe to the circuit at the X2 pin (oscillator output) and

observe the waveform. DO NOT DO THIS! Although in

some cases you may see a useable waveform, due to

the parasitics (usually 10pF to ground) applied with the

scope probe, there will be no useful information in that

waveform other than the fact that the circuit is oscillat-

ing. The X2 output is sensitive to capacitive impedance

so the voltage levels and the frequency will be affected

by the parasitic elements in the scope probe. Applying a

scope probe can possibly cause a faulty oscillator to

start up, hiding other issues (although in the Intersil

RTC’s, the internal circuitry assures startup when using

the proper crystal and layout). The best way to analyze

the RTC circuit is to power it up and read the real time

clock as time advances.

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 supercapacitor for applications where Vcc

may disappear intermittently for short periods of time.

Depending on the value of supercapacitor 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 Vcc to charge the superca-

pacitor, which is connected to the Vback pin. Do not

X1227

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P28

X1227S8I-2.7A

Mfr. #:

Buy X1227S8I-2.7A

Manufacturer:

Renesas / Intersil

Description:

IC RTC CLK/CALENDAR I2C 8-SOIC

Lifecycle:

New from this manufacturer.

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X1227S8I-2.7A

X1227S8I-2.7A

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