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

John_Loffink at Dell.com John_Loffink at Dell.com
Tue Jul 23 14:26:51 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* John_Loffink at Dell.com
*
I agree with Dave and Bill that 10mA can be marginal when considering light
pipe loss.  I also agree that we don't want to add LED drive transistors to
the backplanes.  That just adds another single point of failure to a
difficult to replace backplane.

John Loffink
512-723-2023 phone
512-723-6657 fax
John_Loffink at dell.com



-----Original Message-----
From: Bill Galloway [mailto:BillG at breatech.com]
Sent: Monday, July 22, 2002 9:16 PM
To: Dave_Davis at uk.xyratex.com; Alvin.Cox at seagate.com
Cc: t10 at t10.org
Subject: RE: SAS 3.3V LED driver characteristics - Feedback by 8/2/02
please!


* From the T10 Reflector (t10 at t10.org), posted by:
* "Bill Galloway" <BillG at breatech.com>
*
Dave,

I agree with you that the 10ma is not good enough for a bright LED run
through a light pipe. Nobody really cares because they want to go to
3.3V. What they are forcing box makers to do is to treat the signal
coming from the drive like a logic signal and drive a transistor on the
backplane which will drive the LED. I also agree that the place for the
transistor is on the drive so that they can keep the SFF 8045 voltages
and currents.

Bill Galloway
BREA Technologies, Inc.
P: (281) 530-3063
F: (281) 988-0358
BillG at breatech.com 

-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Dave
Davis
Sent: Monday, July 22, 2002 1:04 PM
To: John Lohmeyer; Alvin.Cox at seagate.com
Cc: T10 Reflector
Subject: RE: SAS 3.3V LED driver characteristics - Feedback by 8/2/02
please!


* From the T10 Reflector (t10 at t10.org), posted by:
* "Dave Davis" <Dave_Davis at uk.xyratex.com>
*
Alvin et al,
	I want to express a concern here on the brightness of LEDs that
this spec might support. Most manufacturers use some type of lightpipe
to transfer the light from the LED to the front of the enclosure. All of
these suffer loss, some due to alignment and most due to material
characteristics. Whilst the LEDs are improving there is still a
challenge in the materials that will push the use of brighter, higher
current LEDs. Whilst these could be driven using additional transistors,
all of us are striving for passive backplanes for increased reliability
and hence are not desirable. 

Has this been considered in the recommendation ? I believe that we
currently run high brightness LEDs at around 19mA and that a reduction
to 10mA would be too difficult to meet.

Regards , Dave Davis , Product Architect,
Storage Solutions Development, Dept 459 ,
Locn 1000/61, XYRATEX ,UK, mailto:dave_davis at uk.xyratex.com TEL:Int 6466
Ext +44 (0)2392 496466 FAX: +44 (0)2392 492284 Http://www.xyratex.com

-----Original Message-----
From: John Lohmeyer [mailto:lohmeyer at t10.org] 
Sent: 22 July 2002 16:57
To: Alvin.Cox at seagate.com
Cc: T10 Reflector
Subject: Re: SAS 3.3V LED driver characteristics - Feedback by 8/2/02
please!

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

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?

John




At 7/19/2002 03:23 PM, you wrote:
>* From the T10 Reflector (t10 at t10.org), posted by:
>* Alvin.Cox at seagate.com
>*
>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 t10.org
LSI Logic Corp.                Voice: +1-719-533-7560
4420 ArrowsWest Dr.              Fax: +1-719-533-7183
Colo Spgs, CO 80907

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