SAS 3.3V LED driver characteristics - Feedback by 8/2/02 please!

John Lohmeyer lohmeyer at
Mon Jul 22 08:56:41 PDT 2002

* From the T10 Reflector (t10 at, posted by:
* John Lohmeyer <lohmeyer at>

I wholeheartedly agree with moving to 3.3-volt LED driver specifications.

However, I have two issues with the Drive LED on specification:

1. The sign in the IOL inequality for the Drive LED on specification is 
backwards to normal practice for chip specs. This inequality should be less 
than or equal to 10 mA, not greater than 10 mA. (This says the chip can 
sink up to 10 mA over the VOL range.)

2. The 0.15 VOL spec is aggressive. Do you really want your chip vendors to 
scrape chips that can only sink 10 mA at 0.16 Volts on the LED driver pin, 
but are otherwise perfectly good parts?


At 7/19/2002 03:23 PM, you wrote:
>* From the T10 Reflector (t10 at, posted by:
>* Alvin.Cox at
>The majority of the SAS PHY working group desires to change the LED driver
>characteristics to be 3.3V compliant rather than 5V compliant. As a new
>interface, this seems to be the best opportunity to change. IC supply
>voltages are lower and LED efficiencies are increasing. One complication is
>the old specification allowed a rather high output-low voltage. At 0.5V
>maximum, it is a significant proportion of the nominal 3.3V supply. The
>current was also rather high when considering the LED's available today.
>The SAS PHY working group makes the following recommendation for
>consideration in the SAS specification for the READY LED electrical
>characteristics. We realize that this may be an aggressive specification at
>this time, but feel that it most likely can be achieved with today's
>commonly used technologies. Check the SAS specification (Section 5) for the
>complete set of READY LED implementation requirements.
>Output characteristics of the READY LED signal (tested through the device
>mated connector)
>     State              Output current             Output voltage
>Drive LED off      -100 µA < IOH < 100 µA         0 < VOH < 3.6 V
>Drive LED on             IOL > 10 mA              0 < VOL < 0.15V
>Alvin Cox
>Seagate Technology, LLC
>* For T10 Reflector information, send a message with
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John Lohmeyer                  Email: lohmeyer at
LSI Logic Corp.                Voice: +1-719-533-7560
4420 ArrowsWest Dr.              Fax: +1-719-533-7183
Colo Spgs, CO 80907

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