SPI-3 single-ended AC test circuit

Gingerich, Kevin k-gingerich at ti.com
Tue Jun 29 13:57:23 PDT 1999


* From the T10 Reflector (t10 at symbios.com), posted by:
* "Gingerich, Kevin" <k-gingerich at ti.com>
*
Gene, I vaguely remember those discussions. I hope I argued for not mixing
the bus load models. The 47 ohm load resistor is in the test circuit to
simulate distributed-parameter load as seen by the driver. Adding a large
lumped capacitance to the test load violates that supposition.

I'm of the opinion that any capacitance in the test load be specified to
account for the instrumentation loading and standardize the measurement. I
think the 15 pF was allowed for cheap scope probes and the 100 pF number
came up because someone didn't want to have to correlate his ATE
measurements to the bench. 

/Kevin/

-----Original Message-----
From: Gene_Milligan at notes.seagate.com
[mailto:Gene_Milligan at notes.seagate.com]
Sent: Friday, June 25, 1999 7:01 PM
To: John Lohmeyer
Cc: T10 Reflector; Barnes, Larry
Subject: Re: SPI-3 single-ended AC test circuit


* From the T10 Reflector (t10 at symbios.com), posted by:
* Gene_Milligan at notes.seagate.com
*
I recall that Kevin tried years ago to get the 15 pF raised to, I think,
>100 pF and it took vigilance to avoid this change. The argument for the
change was that the cable loading was much higher than 15 pF. The argument
against the change was that the 15 pF was the gold standard the slew rates
had been specd during the design phase.

Gene


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