SW00ENB-ZCC Toshiba, SW00ENB-ZCC Datasheet - Page 28

• Manufacturer Part Number: SW00ENB-ZCC
• Description: MCU, MPU & DSP Development Tools CASEWORKS
• Manufacturer: Toshiba

Specifications of SW00ENB-ZCC

• Tool Type: Development Software Support
• Core Architecture: 870
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

3.3.10
3.3.11
3.3.12
Spike currents generated during switching can cause Vcc (Vdd) and GND (Vss) voltage levels to
fluctuate, causing ringing in the output waveform or a delay in response speed. (The power
supply and GND wiring impedance is normally 50
power supply lines with respect to high frequencies must be kept low. This can be accomplished
by using thick and short wiring for the Vcc (Vdd) and GND (Vss) lines and by installing
decoupling capacitors (of approximately 0.01 F to 1 F capacitance) as high-frequency filters
between Vcc (Vdd) and GND (Vss) at strategic locations on the printed circuit board.
For low-frequency filtering, it is a good idea to install a 10- to 100- F capacitor on the printed
circuit board (one capacitor will suffice). If the capacitance is excessively large, however, (e.g.
several thousand F) latch-up can be a problem. Be sure to choose an appropriate capacitance
value.
An important point about wiring is that, in the case of high-speed logic ICs, noise is caused
mainly by reflection and crosstalk, or by the power supply impedance. Reflections cause
increased signal delay, ringing, overshoot and undershoot, thereby reducing the device’s safety
margins with respect to noise. To prevent reflections, reduce the wiring length by increasing the
device mounting density so as to lower the inductance (L) and capacitance (C) in the wiring.
Extreme care must be taken, however, when taking this corrective measure, since it tends to
cause crosstalk between the wires. In practice, there must be a trade-off between these two
factors.
Printed circuit boards with long I/O or signal pattern lines
are vulnerable to induced noise or surges from outside
sources. Consequently, malfunctions or breakdowns can
result from overcurrent or overvoltage, depending on the
types of device used. To protect against noise, lower the
impedance of the pattern line or insert a noise-canceling
circuit. Protective measures must also be taken against
surges.
For details of the appropriate protective measures for a particular device, consult the relevant
databook.
Widespread use of electrical and electronic equipment in recent years has brought with it radio
and TV reception problems due to electromagnetic interference. To use the radio spectrum
effectively and to maintain radio communications quality, each country has formulated
regulations limiting the amount of electromagnetic interference which can be generated by
individual products.
Electromagnetic interference includes conduction noise propagated through power supply and
telephone lines, and noise from direct electromagnetic waves radiated by equipment. Different
measurement methods and corrective measures are used to assess and counteract each specific
type of noise.
Difficulties in controlling electromagnetic interference derive from the fact that there is no
method available which allows designers to calculate, at the design stage, the strength of the
electromagnetic waves which will emanate from each component in a piece of equipment. For this
reason, it is only after the prototype equipment has been completed that the designer can take
measurements using a dedicated instrument to determine the strength of electromagnetic
interference waves. Yet it is possible during system design to incorporate some measures for the
Decoupling
External noise
Electromagnetic interference
3 General Safety Precautions and Usage Considerations
14
to 100 .) For this reason, the impedance of
Input/Output
Signals