ch06.3.htm
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7</A>
</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79174">
</A>
–1.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79176">
</A>
0.50</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79178">
</A>
24.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79180">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79182">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79184">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79186">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=79191">
</A>
<SPAN CLASS="TableHeads">
XC8100</SPAN>
<SUP CLASS="Superscript">
<A HREF="#pgfId=79190" CLASS="footnote">
8</A>
</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79193">
</A>
TTL</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79195">
</A>
R </P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79197">
</A>
2.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79199">
</A>
0.8</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79201">
</A>
3.86</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79203">
</A>
–4.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79205">
</A>
0.50</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79207">
</A>
24.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79209">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79211">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79213">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79215">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=79217">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79219">
</A>
CMOS</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79221">
</A>
C </P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79226">
</A>
3.85<SUP CLASS="Superscript">
<A HREF="CH06.3.htm#21274" CLASS="XRef">
2</A>
</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79231">
</A>
0.9<SUP CLASS="Superscript">
<A HREF="CH06.3.htm#21192" CLASS="XRef">
3</A>
</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79233">
</A>
3.86</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79235">
</A>
–4.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79237">
</A>
0.40</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79239">
</A>
4.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79241">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79243">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79245">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79247">
</A>
</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=79249">
</A>
<SPAN CLASS="TableHeads">
ACT 2/3</SPAN>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79251">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79253">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79255">
</A>
2.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79257">
</A>
0.8</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79259">
</A>
2.4</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79261">
</A>
–8.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79263">
</A>
0.50</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79265">
</A>
12.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79267">
</A>
3.84</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79269">
</A>
–4.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79271">
</A>
0.33</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79273">
</A>
6.0</P>
</TD>
</TR>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableLeft">
<A NAME="pgfId=79279">
</A>
<SPAN CLASS="TableHeads">
FLEX10k</SPAN>
<SUP CLASS="Superscript">
<A HREF="#pgfId=79277" CLASS="footnote">
9</A>
</SUP>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79281">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79283">
</A>
3V/5V</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79285">
</A>
2.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79287">
</A>
0.8</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79289">
</A>
2.4</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79291">
</A>
–4.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79293">
</A>
0.45</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79295">
</A>
12.0</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79297">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79299">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79301">
</A>
</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="Table">
<A NAME="pgfId=79303">
</A>
</P>
</TD>
</TR>
</TABLE>
<P CLASS="Body">
<A NAME="pgfId=32003">
</A>
There is one problem when we mix 3 V and 5 V supplies that is shown in <A HREF="CH06.3.htm#38960" CLASS="XRef">
Figure 6.15</A>
(d). If we apply a voltage to a chip input that exceeds the power supply of a chip, it is possible to power a chip inadvertently through the clamp diodes. In the worst case this may cause a voltage as high as 2.5 V (= 5.5 V – 3.0 V) to appear across the clamp diode, which will cause a very large current (several hundred milliamperes) to flow. One way to prevent damage is to include a series resistor between the chips, typically around 1 k<SPAN CLASS="Symbol">
W </SPAN>
. This solution does not work for all chips in all systems. A difficult problem in ASIC I/O design is constructing <SPAN CLASS="Definition">
5</SPAN>
<A NAME="marker=59953">
</A>
<SPAN CLASS="Definition">
V-tolerant I/O</SPAN>
. Most solutions may never surface (there is little point in patenting a solution to a problem that will go away before the patent is granted).</P>
<P CLASS="Body">
<A NAME="pgfId=31099">
</A>
Similar problems can arise in several other situations:</P>
<UL>
<LI CLASS="BulletFirst">
<A NAME="pgfId=31100">
</A>
when you connect two ASICs with “different” 5 V supplies;</LI>
<LI CLASS="BulletList">
<A NAME="pgfId=31102">
</A>
when you power down one ASIC in a system but not another, or one ASIC powers down faster than another;</LI>
<LI CLASS="BulletLast">
<A NAME="pgfId=31107">
</A>
on system power-up or system reset.</LI>
<TABLE>
<TR>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFigTitleSide">
<A NAME="pgfId=77208">
</A>
FIGURE 6.15 <A NAME="38960">
</A>
Mixed-voltage systems. (a) TTL levels. (b) Low-voltage CMOS levels. (c) A mixed-voltage ASIC. (d) A problem when connecting two chips with different supply voltages—caused by the input clamp diodes.</P>
</TD>
<TD ROWSPAN="1" COLSPAN="1">
<P CLASS="TableFigure">
<A NAME="pgfId=31003">
</A>
</P>
<DIV>
<IMG SRC="CH06-15.gif">
</DIV>
</TD>
</TR>
</TABLE>
</UL>
</DIV>
<HR>
<DIV CLASS="footnotes">
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
1.</SPAN>
<A NAME="pgfId=79005">
</A>
XC2000, XC3000/A have identical thresholds. XC3100/A thresholds are identical to XC3000 except for ±8 mA source–sink current. XC5200 thresholds are identical to XC3100A.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
2.</SPAN>
<A NAME="pgfId=79041">
</A>
<A NAME="21274">
</A>
Defined as 0.7 <SPAN CLASS="EquationVariables">
V</SPAN>
<SUB CLASS="SubscriptVariable">
DD</SUB>
, calculated with <SPAN CLASS="EquationVariables">
V</SPAN>
<SUB CLASS="SubscriptVariable">
DD</SUB>
<SUB CLASS="Subscript">
max</SUB>
= 5.5 V.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
3.</SPAN>
<A NAME="pgfId=79047">
</A>
<A NAME="21192">
</A>
Defined as 0.2 <SPAN CLASS="EquationVariables">
V</SPAN>
<SUB CLASS="SubscriptVariable">
DD</SUB>
, calculated with <SPAN CLASS="EquationVariables">
V</SPAN>
<SUB CLASS="SubscriptVariable">
DD</SUB>
<SUB CLASS="Subscript">
min</SUB>
<SPAN CLASS="EquationNumber">
</SPAN>
= 4.5 V.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
4.</SPAN>
<A NAME="pgfId=79086">
</A>
Defined as <SPAN CLASS="EquationVariables">
V</SPAN>
<SUB CLASS="SubscriptVariable">
DD</SUB>
– 0.2 V, calculated with <SPAN CLASS="EquationVariables">
V</SPAN>
<SUB CLASS="SubscriptVariable">
DD</SUB>
<SUB CLASS="Subscript">
min</SUB>
= 3.0 V.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
5.</SPAN>
<A NAME="pgfId=79097">
</A>
XC4000, XC4000A have identical I/O thresholds except XC4000A has –24 mA sink current. </P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
6.</SPAN>
<A NAME="pgfId=79126">
</A>
XC4000H/E have identical I/O thresholds except XC4000E has –12 mA sink current. Options are independent.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
7.</SPAN>
<A NAME="pgfId=79171">
</A>
Defined as <SPAN CLASS="EquationVariables">
VDD</SPAN>
– 0.5 V, calculated with <SPAN CLASS="EquationVariables">
VDD</SPAN>
<SUB CLASS="Subscript">
min</SUB>
= 4.5 V.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
8.</SPAN>
<A NAME="pgfId=79190">
</A>
Input and output options are independent.</P>
</DIV>
<DIV CLASS="footnote">
<P CLASS="TableFootnote">
<SPAN CLASS="footnoteNumber">
9.</SPAN>
<A NAME="pgfId=79277">
</A>
MAX 9000 has identical thresholds to FLEX 10k.</P>
<P CLASS="TableFootLast">
<A NAME="pgfId=79278">
</A>
<SPAN CLASS="Emphasis">
Note:</SPAN>
All voltages in volts, all currents in milliamperes.</P>
</DIV>
</DIV>
<HR><P>[ <A HREF="CH06.htm">Chapter start</A> ] [ <A HREF="CH06.2.htm">Previous page</A> ] [ <A HREF="CH06.4.htm">Next page</A> ]</P></BODY>
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