SP506CF datasheet(18/30 Pages) SIPEX

18 / 30 page

SP505/6/7APN/03

SP505, SP506, SP507 Application Note

the power supply unit and radiated out to the

environment. For serial port datacom applications,

both emissions and immunity must be carefully

considered during the design-in phase.

The conducted emissions in the most single supply

interface transceivers are generated from the internal

charge pump. Although the charge pump is enhanced

over previous generation pumps, the SP506 and

SP507 charge pump architecture will inherently have

small ripples on the V

DD and VSS outputs. The ripples

are due to the switching of the internal charge pump

transistors that are transferring energy. The charge

pump oscillates at 20kHz in standby mode (without

loads to the drivers) and will automatically increase

frequency to 300kHz when loaded. The ripples will

coincide with the oscillator frequency. The driver

output circuitry receives biasing from the charge

pump outputs, V

DD and VSS, for the V.28 and V.10

bipolar voltage swings. The V

DD or VSS supply ripple

could be superimposed onto the driver outputs,

depending on the ripple amplitude. Larger capacitor

values will suppress the ripple of the pump and thus,

minimize the ripple amplitude on the data lines.

For the SP505, SP506, and SP507, the amplitude of

the ripple is below 100mV when using 22

µF pump

capacitors (refer to Figure 34).

Depending on the application requirements, EMI/EMC

filtering may be needed. The SP506 and SP507 are

usually not affected by radiated disturbance nor do

they emit radiated noise/interference. But a shielded

enclosure (Faraday Cage) will help the immunity from

radiated disturbance as well as emissions of radiated

noise. Conducted noise can be surpressed by using

ferrite beads, low pass filters using RC circuits,

inductor circuits, or common mode chokes on the

signal lines.

One surface mount common-mode choke (CMC)

designed for data signaling applications in the 10Mbps

to 15Mbps band is TDK's ZJYS51R5-4P. This 8-pin

SOIC package contains a two pairs of inductors for

two differential signals. Since clock and data are

switching most frequently, the number of pairs needed

are two for DTE (TxD and TxCE drivers) or three for

DCE (TxD, TxCE, TxC drivers), which means one

IC for DTE and two ICs for DCE. Refer to Figure 31

for connection and to TDK's datasheet for the

ZJYS51R5-4P CMC.

(http://www.tdk.co.jp/tefe02/e971_zjys.pdf)

Semtech's SMDA15C-7 is used in Figure 30 to protect

the handshaking signals. Since the SMDA15C-7 only

provides protection for seven lines, the SMDA15C-5

is used for the remaining lines. Both are 8-pin SOIC

packages. Other configurations or manufacturers

can be used. Refer to the TVS datasheets.

(http://www.semtech.com/pdf/tvs/lcda15c6.pdf)

Figure 6 also shows optional TransZorbs™ or TVS

devices on the SP506 to further protect the serial

port from any ESD or overvoltage transients that

may occur in any application. The SP505, SP506

and SP507 are internally rated for 8kV based on

Human Body Model and 2kV Air Discharge per

IEC1000-4-2. Adding transzorbs to the I/O lines will

protect the serial port to over 15kV of ESD transients

per IEC1000-4-2 Air Discharge and 8kV per Contact

Discharge. The TVS devices on the driver inputs

and receiver outputs are included for hot-insertion

of the interface module/board applications.

The internal junction of the SP505, SP506 and SP507

receiver inputs and driver outputs are similar to the

I-V curve on Figure 28. However, TVS devices are

always recommended where ever possible as it is

difficult to predict transient induced phenomena in

any environment.

It is also important to know that these TVS devices

are also specified for IEC1000-4-4 Electrical Fast

Transients and IEC1000-4-5 Surge (Lightning)

protection. Refer to the TVS datasheets from Semtech

for details (www.semtech.com).

Electromagnetic Interference is also a concern for

networking equipment. The EMI noise is cause by

radiated emissions or power-line conducted emissions

from the system. The equipment has to be characterized

for both immunity and emissions. Immunity is the

system's tolerance to incoming interference or

disturbances generated from outside sources.

Emissions are the system's own generation of these

types of disturbances. Specifically, the documents

EN61000-4-3 and EN61000-4-6 pertain to Radiated

electric field test and Line Conducted electric field

test, respectively, for immunity. The EN55022

specification pertains to emissions and specifies

Line Conducted Emission, which are noise or

disturbances generated from a power supply unit,

conducted in the cables; and Radiated emissions,

which pertain to noise or disturbances generated by

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