SP506 View Datasheet(PDF) - Signal Processing Technologies
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SP506 Datasheet PDF : 30 Pages
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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
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 VDD 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, VDD and VSS, for the V.28 and V.10
bipolar voltage swings. The VDD 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 22µF 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)
SP505/6/7APN/03
SP505, SP506, SP507 Application Note
18
© Copyright 2000 Sipex Corporation
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