Re: Simple analog signaling for an AC adapter
As an analog and mixed-mode designer I learned quite some time ago that it is preferable not to use an analog system when a digital one can do a better job. Tolerances, repertoire of possible responses, long time constants, and safety are all rather easy to handle and expand through digital means, but can become very complicated and costly through analog ones. My fears in allowing for a completely analog 'communications' system to coexist with a digital one would be:
(1) we compromise overall safety
(2) we make it harder to satisfy the stated goals (e.g., life expectancy of standard, adapter/device compatibility over life of standard, and certification support)
(3) we could be hindering standard adoption rather than promoting it.
(4) we might have to create a full digital communications standard from scratch (thus increasing overall cost)
(5) we would be increasing the cost of adapters and devices that wish to implement the digital parts of the standard.
(6) we could be limiting what can be accomplished by the digital communication system (e.g., speed, compatibility)
We have to keep in mind the point that Leonard and Piotr have made, once devices and adapters are being produced in quantity, the differential cost between an analog method and a digital one will mostly disappear. At that point, all adapters and devices will have to keep around analog communications subsystems just to remain compatible, with no real added benefit.
I would expect the cost curve to follow the same adoption path as many other technologies (1) first the high-cost high-margin devices will adopt the standard (for which functionality would be key), (2) added-value multi-port adapters will follow suit, (3) both of these will create a market for ICs and off-the shelf subsystems for UPAMD thus reducing implementation costs, (4) lower cost devices and adapters will start adopting the standard. I would expect such adoption curve to be followed with or without analog communications, and I actually see that requiring analog communications as part of the standard could hinder rather than accelerate adoption.
Although I can see how a purely analog system can work, I cannot see how it can easily satisfy goal 5 (higher power applied only when it is safe to do so); goal 4, as the aging of analog components will make it harder to guarantee safety or compliance for the life of the adapter; or goal 6, as the certification of analog systems across age and component variations would become harder to accomplish. (An example that comes to mind is the UCD9248 IC from TI, as it states in its errata that it cannot reliably identify a considerable section of its address range because it relies on resistors and analog values to set it.)
Gary and/or Arjan, can you come up with a more fleshed-out proposal on alternatives for how this analog communications would work? A reference design would be ideal, but at the very least it should attempt to address safety and digital communications compatibility.
For the sake of argument, if we assume that digital communications would be following a differential CAN standard over a separate pair, what modifications would be required to make analog communications work?
We can discuss on this Tuesday's communications subgroup meeting.
Edgar
On Dec 8, 2010, at 8:00 PM, <Leonard_Tsai@xxxxxxxxxx> <Leonard_Tsai@xxxxxxxxxx> wrote:
> Coming from ODM point of view, the digital communication cost will disappear
> fast than you expect. Most of the power adapter today already include
> digitally control IC. Adding an interface of digital communication channel
> may increase small $ in the beginning but will disappear once healthy
> competition starts.
>
> Analog way is a bigger problem as it creates testing requirement for
> production line and room for error.
>
> Leonard
>
> -----Original Message-----
> From: upamd@xxxxxxxx [mailto:upamd@xxxxxxxx] On Behalf Of Tomlins, Garry
> Sent: Wednesday, December 08, 2010 8:20 PM
> To: Piotr Karocki; upamd@xxxxxxxx
> Subject: RE: Simple analog signaling for an AC adapter
>
> I agree with Lee and Arjan:
> This is heading down a path of unnecessary and complex functionality that
> leads in turn to a complex and expensive implementation. I beleive it will
> not be attractive to the major equipment ODM's who will need to adopt this if
> it is to be a success.
> We should have a simple analog low cost option.
> In my experience in servicing the adapter market for high volume electronics
> adding a pin, a wire, a resistor a pin to an IC is a big deal - let alone a
> separate communications system!
> My vote is for a simple analog option as described. I believe this will have
> a good chance of adoption and would be a success for the project.
> Garry
>
>
>
> Texas Instruments (Cork) Limited, Registered in Ireland under Registration
> Number: 294554, Registered Office: Riverside One, Sir John Rogerson's Quay,
> Dublin 2
>
> -----Original Message-----
>
> From: upamd@xxxxxxxx [mailto:upamd@xxxxxxxx] On Behalf Of Piotr Karocki
> Sent: 08 December 2010 11:50
> To: upamd@xxxxxxxx
> Subject: Re: Simple analog signaling for an AC adapter
>
> I don't agree with Arjan.
>
> We could either "describe current situation" or "shape the future".
>
> Our standard could allow resistor-based "communication", something,
> something, and full communication (required voltage etc.).
> But as one of goals is to allow to connect every device to every supply (and,
> in near future, connections in form of grid; power hubs, power storage etc.),
> every supply has to have full communication option. Making provision to
> understand simpler communication (as resistor based) makes supply more
> costly.
> Say, we have hundred million devices. Half of them - resistor based
> communication, and tenth of them - full model of communication (4/10 of them
> some 'in-between' form).
> Or, we could force whole 100 000 000 devices to have full model of
> communication.
>
> But it is the only way to make this full communication cheaper - as it would
> be "more mass" production. It would be ONE standard...
> And the only way to make possible to connect device from 2010 to power supply
> from 2050 or vice versa. This scenario is not impossible - when standard
> becomes "grid version"... How often you change wiring in your house?
>
> ________________________________
> From: upamd@xxxxxxxx [upamd@xxxxxxxx] On Behalf Of arjan strijker
> [arjan.strijker@xxxxxxx]
> Sent: Wednesday, December 08, 2010 12:26 PM
> To: Atkinson, Lee; Bob Davis; upamd@xxxxxxxx
> Subject: RE: Simple analog signaling for an AC adapter
>
> I agree with Lee that UPAMD should also support low cost devices.
> A simple resistor to ground inside the device could tell the adapter what
> voltage it requires.
> More sophisticated device can still do power negotiation etc.
>
> With regards,
> Arjan Strijker
>
> From: upamd@xxxxxxxx [mailto:upamd@xxxxxxxx] On Behalf Of Atkinson, Lee
> Sent: Wednesday, December 08, 2010 12:08 AM
> To: Bob Davis; upamd@xxxxxxxx
> Subject: Simple analog signaling for an AC adapter
>
> Bob, here is a quick presentation on the method that HP uses for
> signaling from the adapter to the notebook. We've had this system in place
> since 2005 or 2006, and have shipped maybe close to 150million systems that
> use the common "HP Smart" system (including notebooks, all in one desktops,
> and small form-factor desktops).
>
> My suggestion is that we at least baseline a system that will allow some
> scalability of the communication method; at least, allow very low cost
> devices to connect to a UPAMD power source and work reliably even if their
> functionality is limited. I'm not sure that a lot of simple devices that
> would use UPAMD have a need for all the messages that the adapter could
> provide, or would be able to negotiate variable power consumption. I think we
> all agree, there is very little precedence for using sophisticated signaling
> in the common DC powered devices now in the market. Though I agree the simple
> methods are limited, if we can deliver a scalable solution there will be
> fewer reasons for the industry to not adopt UPAMD.
>
> Thanks again--Lee
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