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© 2007 Yamar Electronics Ltd.

10

DS-ISL40 R1.6

4.5 Ceramic Filter

The ISL40 is designed to operate with one ceramic filter for transmission and reception. However, if

switching between two channels is desired, two ceramic filters are required. The minimum allowable

bandwidth of the ceramic filters is +/-70 kHz @ 3dB. Narrower bandwidth limits the maximal bit rate.

The ISL40 selectable frequencies are designed according to the market available ceramic filters.

Nominal

freq.

3 db BW 20db

BW

Insertion

loss

Stop band

attenuation

In/Out

imped.

Murata

part #

Oscilent

part #

MHz

KHz

min.

KHz

max.

dB

max.

dB

min.

Ohm

*3.58

+/-40

530

6.0

25

530

SFSH3.58MCB

4.5

+/-70

750

6.0

30

1000

SFSL4.5MDB

773-0045

5.5

+/-80

750

6.0

30

600

SFSL5.5MDB

773-0055

6.0

+/-80

750

6.0

30

470

SFSL6.0MDB

773-0060

6.5

+/-80

800

6.0

30

470

SFSL6.5MDB

773-0065

•

The 3.58MHz frequency can be operated with 9.6Kbps and 19.2Kbps only

4.6

Oscillator

The ISL40 is designed to operate with a low cost 32.768KHz crystal connected between OscIn and

OscOut pins. This type of crystal has the advantage of very low power consumption and low cost.

However there are also drawbacks. It is very sensitive to noise and has a temperature dependency that

should be carefully considered when selecting the crystal.

The following guidelines should be used when designing the PCB:

1.

Design the trace length as short as possible.

2.

Avoid thin line on resonator traces (< 0.010"), keep them as wide as possible.

3.

To avoid noise, protect these signals with Ground shields.

The exact values of C1, C2, R1 and R2 should be determined according to the crystal manufacturer.

4.7

Recommended 32.768KHz Crystal Specifications

Type

Value

Nominal Frequency:

32.768KHz

Frequency tolerance @25ºC

+/-20 ppm

Load capacitance

12.5 pF

Serial resistance

50K Ohm (max.)

Drive level

1uW (max.)

Quality factor

50,000 (max.)

Turnover temperature

+25ºC +/- 5ºC

Parabolic constant

-0.04 ppm/ºC² (max.)

Aging

+/-3 ppm in first year (max.)

Operating temperature

-40ºC to + 85ºC

Storage temperature

-55ºC to + 125ºC

The overall frequency tolerance should not exceed 200ppm.

4.8

Communication performance

The maximal cable length between extreme devices depends mainly on the AC impedance of loads

connected to that line and number of nodes. The DC cable length has less effect on communication.

The SIG40 needs at least 20mVpp for proper reception. Good communication should be achieved if an

oscilloscope at the SIG40 receiver can see the transmitted signal within the noise.