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

Alvin.Cox at Alvin.Cox at
Fri Jul 19 13:23:31 PDT 2002

* 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

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