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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Future power supply concepts for automotive electronics
References: <3D878889.98EC63A6@erckert-ibe.de> <3D8E3436.32FD08A6@webaccess.net> <3D8F86FC.CBC83B71@erckert-ibe.de> <3D8FDF51.A028E654@webaccess.net> <3D90E72B.9C71568A@erckert-ibe.de>
Date: Wed, 25 Sep 2002 02:13:53 GMT
NNTP-Posting-Date: Tue, 24 Sep 2002 19:13:53 PDT
> How do you interface the 12V actuator drivers? Directly from your logic
> IC (today 3.3V port, future even lower)?
> Serial bus (SPI or SCI) is nice looking at pin count but carries a lot
> of logic into a high voltage technology and there it costs money.
I have DACs built in 0.35 micron that have a 2 volt swing given a 3.3
volt supply. This is the industry standard, it seems, in this product
space. This is a single wire interface to a DMOS or bipolar driver. The
0.18 generation is now expected to keep some 0.35 structures in order to
remain compatible with available drivers. The same chip that has the
DACs has a ADC, sample and holds and an analog mux. Separating the ADC
and its paraphernalia makes no sense because it essentially splits one
chip into two because there is no other single chip to absorb the
functions. The ideal is analog in from all sources and analog out to all
drivers with digital processing in the middle and all in one chip with
the logical next generation combining the two large logic chips along
with the analog functions. This is better than combining all the logic
and breaking out the analog which has 50 or so control signals. Instead
of reducing pin count (good), it would increase pin count (very bad
because going up to over 400 pins on one chip brings cost up).
> Actuator drivers generate high dI/dt which cause inductive supply bounce
> and ground bounce. Is there acceptance to interface the low voltage
> signals with differential lines (similar to old RS-423-A or CAN twisted
> pair drivers) or do you just low pass filter a single wire to get rid of
> signal integrity problems. In automotive I have seen ground bounce up to
> +-3V on one board and up to +-15V from board to board when a 0.05 Ohm
> switch hits a short circuit!
Maybe optical fiber. Not too bad if the distances are short enough to
use LEDs. Ground bounce is not a big deal if circuits have their signals
isolated from ground and power. Obviously in what I do where distances
are inches, I will use copper. In a very noisy environment, fiber is
> Do you power down low voltage logic in stand by or do you keep it alive
> although it leaks even while it is not clocked (I have to come down to
> less than 100uA at 85 Celsius with assynchronuous interrupts still being
> I think of moving the interrupt handler into the power IC so that I get
> rid of leakages. Problem is that I have no clue how much programability
> I will need. (simple micro or is a finite state machine and some
> configuration bytes sufficient?)
> How about bus wake up? Where should the protocol handler sit? I think it
> must be on the same chip as the interrupt handler because it must
> monitor the bus while the CPU is off.
You have a bigger problem in an automobile than in a line powered
device. It is considered rud for your electronics to discharge the
battery whereas I'm still fine going to the next generation letting the
processor (core) internal sleep logic simply shut down the clock. The
oscillator has to run but the internal clock distribution can be halted
at any time. A kind of worse problem is power modes for linear drivers
because they have to shut down and come back up without doing physical
damage. That can be difficult.
> Blue lasers need about 3.6V. So it looks like 5V will stay as a mass
> market technology (cheap, that's good!). But I don't think you will
> drive it directly from your logic IC. The lasers I know need to be kept
> close to inversion or in inversion (otherwise pumping them up from 0
> will steal you some ns until you have a good beam). So they require
> quite some analog circuitry anyway.
In CDs and DVDs, the laser driver (Elantec and Temic are the ones I know
a little about) fall back to read power between pulses Read power is
between a couple of hundred microwatts out of the lens up to about a
milliwatt. Read power is required because the servo system is sitting on
its hands waiting for focus and track position information without
which, it will wander aimlessly into the weeds. So after laser on during
system initialization, the laser is never below read power which is over
threshhold (in inversion I presume). Actually, it is done with switched
current sources. The power levels are "servoed" there being maybe four
in some systems. The chip that does the low level currents to the driver
is mixed signal and runs on 3.3 volts. It has 5 volts to to support PECL
but that may go away.
> Analog on 0.18um is expensive. You have to pay submicron mask allignment
> without getting the benefit of shrinking. This only makes sense if you
> can save more interfacing bond pad area than the area you need putting
> the analog stuff on the 0.18um.
The masks for 0.18 seem to be less than double the 0.35 price. The masks
for SiGe are scary, however. The good thing is that if you get the
underlayers right in the first mask set, metal changes are nominal.
About $30,000 per affected layer. If you are really lucky, you can fix
an error in just one metal mask. Of course, the last time I had a
complaint, they decided to do a FIB before ordering masks. I netted one
good part from three that were FIBed and I'm still stuck with it as a
wafer slowly grinds its way along.
> My current conclusion is in the future we will see digtal technologies
> operating between 1V and 1.8V, Analog signal processing operating at 5V
> and power drivers operating at 17V (your 12V+margin), 40V (12V
> automotive plus transient margin) and 60V (42V automotive + transient
> Interfacing could be either
> digital --- 5V analog --- power
> (let's call it topology 'chain')
> digital --- 5V analog
> -- power
> (let's call it topology 'star')
Clearly the new technologies present challenges especially in the
incredibly harsh environment of an automobile. Somewhat similar
challenges exist in consumer electronics. Going to 0.18 while retaining
0.35 analog on the same chip is a good compromise at the system level in
my work. It is unclear what to do at 90 nanometers.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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