SAS 3.3V-compliant LED driver question - Please respond!

mfitzpatrick at fcpa.fujitsu.com mfitzpatrick at fcpa.fujitsu.com
Wed Jul 10 09:48:21 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* mfitzpatrick at fcpa.fujitsu.com
*
Alvin,

Fujitsu supports changing the LED driver to be compatible with 3.3V.

Mike Fitzpatrick
Fujitsu Computer Products of America.


----- Forwarded by Michael Fitzpatrick/Orch/SJ/FCPA/Fujitsu on 07/10/2002
09:45 AM -----
|---------+------------------------------->
|         |                               |
|         |           Alvin.Cox at seagate.co|
|         |                              m|
|         |                       Sent by:|
|         |              owner-t10 at t10.org|
|         |                               |
|         |                               |
|         |                     07/08/2002|
|         |                       09:20 AM|
|         |                               |
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  |     To:      t10 at t10.org                                                                                                                  |
  |     cc:                                                                                                                                   |
  |       Subject:SAS 3.3V-compliant LED driver question - Please respond!                                                                    |
  >-------------------------------------------------------------------------------------------------------------------------------------------|




* From the T10 Reflector (t10 at t10.org), posted by:
* Alvin.Cox at seagate.com
*
Since we are developing a new interface, the SAS PHY group would like to
change the LED driver requirements to be compatible with 3.3V rather than
5V. Efficiency improvements in LED's plus the lowering of interface and IC
supply voltages makes this new interface development a great opportunity to
update the LED driver characteristics. The current specification is stated
below:

          Output characteristics of the READY LED signal

    State              Output current             Output voltage
Drive LED off      -100 µA < IOH < 100 µA         0 < VOH < 5.5 V
Drive LED on             IOL > 30 mA              0 < VOL < 0.5V

To achieve an integrated solution the following changes are proposed. The
SAS PHY working group need feedback from IC suppliers regarding the
feasibility of the LED on output voltage at the specified output currents.
We also solicit feedback from system integrators regarding the 3.6V maximum
off voltage. The configuration would be similar to todays implementation
where the driver is an open collector or open drain configuration which may
be connected to an LED with current limiting resistor or, in some
instances, directly to GROUND. References are measured at the drive
connector (through the mated pair). If the output voltage cannot be
achieved at the given currents, please define what voltage level is
realistic.


          Output characteristics of the READY LED signal

    State              Output current             Output voltage

Drive LED off      -100 µA < IOH < 100 µA         0 < VOH < 3.6 V

Drive LED on             IOL > 20 mA              0 < VOL < 0.20V
   OR
Drive LED on             IOL > 10 mA              0 < VOL < 0.15V

Alvin Cox
Seagate Technology, LLC
Phone  (405) 324-3413
Pager  (888) 787-9434

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