SE active negation output characteristics

[Aloisi, Paul]

* From the T10 Reflector (t10 at t10.org), posted by:
* "Aloisi, Paul" <paul_aloisi at ti.com>
*
Jeff,

>From 2.0 to 3.0 Volts the current is not limited, it can be anywhere in the
white area. 3.0 to 3.24 volts the current is limited to 20 mA, from 3.24 to
3.7 volts the current is limited to 7 mA. 

This allows high current for the transition region, it prevents overdriving
the signal, which helps on the next assertion cycle. We really wanted the
maximum negated signal to be in the 2.5 to 3.0 Volt area limiting the
voltage swing. This allows the best assertion signal range. These are not in
conflict with Table 18.

Paul Aloisi


> -----Original Message-----
> From:	Jeff Schroeder [SMTP:jeffrey.schroeder at st.com]
> Sent:	Friday, October 29, 1999 4:56 PM
> To:	T10 mailing list
> Subject:	SE active negation output characteristics
> 
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Jeff Schroeder <jeffrey.schroeder at st.com>
> *
> I'm hoping somebody can help shed some light on what appears to me to be
> some conflicting requirements for the single ended active negation
> output characteristics.
> 
> Referencing SPI-3 rev. 10: Table 18 says, "b) Voh (high-level output
> voltage) = 2,5 V D.C. to 3,7 V D.C. (signal negated). See figure 26 for
> Ioh." However, figure 26 clearly shows the range to be 2.0 V to 3.7 V,
> at least when the current is below 7 mA. Adding to the confusion is that
> the spec in table 18 does not specify Ioh.
> 
> So, I did a little digging in the archives to see if I could find where
> this originated. Revision 1 of the Fast-20 spec had four rules that
> governed Voh and Ioh for active negation. Among them were these two:
>   "b) Voh (high-level output voltage) = 2,5 to 3,7 V d.c. (signal
>       negated).
>    c) Voh (high-level output voltage) = 2,0 to 3,24 V d.c. at Ioh = 7 mA
>       (signal negated);"
> 
> These two rules are not necessarily in conflict, since rule c) does not
> specify the current as Ioh < 7 mA, but as Ioh = 7 mA. After some
> discussion and adjusting of the voltage and current values, rules c),
> d), and e) were transformed into what is today figure 26 in SPI-3.
> However, rule b) still persists also, and it appears to be in conflict
> with figure 26, which shows the minimum Voh to be 2.0 V for all Ioh < 7
> mA.
> 
> Am I missing something here? Will the real Voh requirement please stand
> up?
> 
> Thanks,
> Jeff
> -- 
> Jeff Schroeder
> TPA Americas
> STMicroelectronics, Inc., San Jose, CA
> Email: jeffrey.schroeder at st.com  Phone: 408-487-3965 Fax: 408-441-8470
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