Concerning quoting, the absolute worst is relying on Microsoft's
Hotmail or Outlook to quote in a way which only works for top-posting
(which is also not good). I ditched Hotmail, partly because I could
not find any way to change the quoting scheme to precede lines with
'>'. Anybody know how to do that in Hotmail and in MS Outlook? > The two C32 I had tested heavily in the last days
worked fine even
> with 22nF on Vdd. Another C32 is running with 100nF, and a fourth
> with 220nF. But that's no significant quantity.
>
> Regarding the symptoms: I guess you will get random errors, so it
> will be hard to assign.
At first I mentioned my 0.1uF because I thought it would be
significantly more than 400nF. I guess I was thinking of pF (400e-12).
I wouldn't think the two 0.1uF have been trouble for me either. I have
had crashes (CPU runs astray), but think it is from noise such as EST,
often through Gnd. I can shock myself on the grounded bolt on the 7805
heatsink, and my prototype crashes. With all the possible causes
building up so fast, it's hard to troubleshoot.
> At this rate has anyone seen failures as a
consequence of not meeting
> this requirement? If so, what sort of symptoms have been seen?
We are using 2*100nF on a DT128 design, hundreds (from different mask
revisions) are in use, no failure.
The two C32 I had tested heavily in the last days worked fine even
with 22nF on Vdd. Another C32 is running with 100nF, and a fourth
with 220nF. But that's no significant quantity.
Regarding the symptoms: I guess you will get random errors, so it
will be hard to assign.
Oliver
--
Oliver Betz, Muenchen
Reply by Jonathan Masters●November 10, 20062006-11-10
-----Original Message-----
From: 6... [mailto:6...] On Behalf
Of Oliver Betz
Sent: Saturday, 11 November 2006 4:26 AM
To: 6...
Subject: Re: [68HC12] Re: Vdd (core voltage) decoupling requirements
Jefferson Smith wrote:
> > you are right, I missed this one. And since there
is not stated that
> > this value is "per pin on a package with two Vdd
pins", one could
> > think that 100nF total capacitance is sufficient.
>
> Is it safe to just use 0.1uF in all my designs to be sure? I supposed
no, the data sheet says 400nF minimum.
> the only reason to need less is if smaller size is
desired.
right. Or higher voltage => likely more robust device.
Oliver
--
Oliver Betz, Muenchen
At this rate has anyone seen failures as a consequence of not meeting
this requirement? If so, what sort of symptoms have been seen?
Jonathan
Reply by Oliver Betz●November 10, 20062006-11-10
Jefferson Smith wrote:
> > you are right, I missed this one. And since there
is not stated that
> > this value is "per pin on a package with two Vdd pins", one could
> > think that 100nF total capacitance is sufficient.
>
> Is it safe to just use 0.1uF in all my designs to be sure? I supposed
no, the data sheet says 400nF minimum.
> the only reason to need less is if smaller size is
desired.
right. Or higher voltage => likely more robust device.
Oliver
--
Oliver Betz, Muenchen
Reply by Jefferson Smith●November 10, 20062006-11-10
--- In 6..., "Oliver Betz" wrote: > you are right, I missed this one. And since there is
not stated that
> this value is "per pin on a package with two Vdd pins", one could
> think that 100nF total capacitance is sufficient.
Is it safe to just use 0.1uF in all my designs to be sure? I supposed
the only reason to need less is if smaller size is desired.
Reply by Oliver Betz●November 9, 20062006-11-09
Edward Karpicz wrote:
[...]
> Sorry, checked again and not a number of times, but
at least datasheet
> rev1.20 p466:
>
> "16.2.3 VDD, VSS - Regulator Output1 (Core Logic)
>
> Signals VDD/VSS are the primary outputs of VREG3V3V2 that provide the power
> supply for the core logic. These signals are connected to device pins to
> allow external decoupling capacitors (100 nF...220 nF, X7R ceramic)."
you are right, I missed this one. And since there is not stated that
this value is "per pin on a package with two Vdd pins", one could
think that 100nF total capacitance is sufficient.
BTW: I found one situation where 400nF makes the voltage regulator
output "nicer": waking up from STOP mode (where the core voltage is
reduced by ~200mV), it seems that the voltage regulator switches
slower to full power mode than the core starts consuming power,
therefore the voltage drops slightly. I measured 74mV drop after 40us
with a 47nF decoupling capacitor (16MHz crystal). Screenshots
available on request.
Although I don't think that this could be a problem, I can't be
sure.
And I don't know whether _that_ is the reason why Motorola/Freescale
states 400nF min. capacitance.
Oliver
--
Oliver Betz, Muenchen
Reply by Edward Karpicz●November 9, 20062006-11-09
Oliver Betz wrote:
> Edward Karpicz wrote:
>
>> > did anybody scrutinize closely why Freecale tells us to use at least
>> > (!) 400nF to decouple the 2,5V core voltage?
>>
>> Hm, where did you find this?
> you also found it, C32 data sheet. Yeah, thanks. I already have units in field and in production, C32 in
QFP48
and only 220nF on VDD1. Wouldn't look at it again if you didn't start
this
thread. Oops, rev1.20 p68: "In 48LQFP and 52LQFP package versions, VDD2 is
not available. Thus 470nF must be connected to VDD1." >
>> Datasheet I have tells a number of times to
>> decouple with 100-220nF. Are you talking about Voltage Regulator Min
>
> where did you find this? "Early documents" as EB376 or data sheets of
> other derivatives, usually "per pin" where two pins are supplied for
> Vdd (2,5V core)?
>
Sorry, checked again and not a number of times, but at least datasheet
rev1.20 p466:
"16.2.3 VDD, VSS - Regulator Output1 (Core Logic)
Signals VDD/VSS are the primary outputs of VREG3V3V2 that provide the power
supply for the core logic. These signals are connected to device pins to
allow external decoupling capacitors (100 nF...220 nF, X7R ceramic)."
>> Capacitive Load? C32 datasheet v1.20, p670. Min
value here is bit
>> confusing.
>
> No, it's not confusing - it's the minimum allowed capacitance.
Sorry for this nonsens, a lack of sleep.
[skip]
Edward
>
> Oliver
> --
> Oliver Betz, Muenchen
Reply by Edward Karpicz●November 9, 20062006-11-09
Andrew,
thanks for correcting me. I should sleep more.
Edward
----- Original Message -----
From: "Andrew Lohmann"
To: <6...>
Sent: Thursday, November 09, 2006 2:00 PM
Subject: Re: [68HC12] Vdd (core voltage) decoupling requirements > >Edward Karpicz wrote:
> >> Oliver Betz wrote:
>
> >> Hello All,
> >
> > did anybody scrutinize closely why Freescale tells us to use at least
> > (!) 400nF to decouple the 2,5V core voltage?
>
> >Hm, where did you find this? Data sheet I have tells a number of times to
> decouple with 100-220nF. Are you talking about Voltage Regulator Min
> Capacitive Load? C32 data sheet v1.20, p670. Min value here is bit
> confusing.
> Usually amplifiers have specified max capacitance of load they are able to
> drive, lower C is and must be OK. Does max value in table A-24 mean that
> some C32 VREGs are able to drive 12uF and some to drive only 400nF? If so
> then max and typical columns are of no use.
>
> Op amps are not really a good comparison, but you should find that an op
> amp may become stable with a very high capacitive load, this aspect is
> not documented. The best comparison is with a band gap references the
> loading capacitance should be less than a certain amount or greater than
> a higher amount. As you need some decoupling capacitance then the
> greater value makes the internal amplifier stable. Although I doubt that
> there is any limit to how high the capacitance value can be, but it is
> always best to do what the manufacturer recommends.
>
> Andrew Lohmann AMIIE
> Design Engineer
>
> PLEASE NOTE NEW EMAIL ADDRESS IS:
> a...@bellinghamandstanley.co.uk
>
> Bellingham + Stanley Ltd.
> Longfield Road, Tunbridge Wells, Kent, TN2 3EY, England.
> Tel: +44 (0) 1892 500400
> Fax: +44 (0) 1892 543115
> Website: www.bs-ltd.com
>
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Reply by Oliver Betz●November 9, 20062006-11-09
Edward Karpicz wrote:
> > did anybody scrutinize closely why Freecale tells
us to use at least
> > (!) 400nF to decouple the 2,5V core voltage?
>
> Hm, where did you find this? you also found it, C32 data sheet.
> Datasheet I have tells a number of times to
> decouple with 100-220nF. Are you talking about Voltage Regulator Min
where did you find this? "Early documents" as EB376 or data sheets of
other derivatives, usually "per pin" where two pins are supplied for
Vdd (2,5V core)?
> Capacitive Load? C32 datasheet v1.20, p670. Min value
here is bit confusing.
No, it's not confusing - it's the minimum allowed capacitance.
> Usually amplifiers have specified max capacitance of
load they are able to
Not voltage regulators.
> drive, lower C is and must be OK.
Not for all voltage regulators.
> Does max value in table A-24 mean that
> some C32 VREGs are able to drive 12uF and some to drive only 400nF? If so
No, it states that 400nF..12uF is acceptable, 200nF ot 20uF are not
acceptable.
Oliver
--
Oliver Betz, Muenchen
Reply by Andrew Lohmann●November 9, 20062006-11-09
>Edward Karpicz wrote: >> Oliver Betz wrote:
>> Hello All,
>
> did anybody scrutinize closely why Freescale tells us to use at least
> (!) 400nF to decouple the 2,5V core voltage?
>Hm, where did you find this? Data sheet I have tells a number of times to
decouple with 100-220nF. Are you talking about Voltage Regulator Min
Capacitive Load? C32 data sheet v1.20, p670. Min value here is bit
confusing.
Usually amplifiers have specified max capacitance of load they are able to
drive, lower C is and must be OK. Does max value in table A-24 mean that
some C32 VREGs are able to drive 12uF and some to drive only 400nF? If so
then max and typical columns are of no use.
Op amps are not really a good comparison, but you should find that an op
amp may become stable with a very high capacitive load, this aspect is
not documented. The best comparison is with a band gap references the
loading capacitance should be less than a certain amount or greater than
a higher amount. As you need some decoupling capacitance then the
greater value makes the internal amplifier stable. Although I doubt that
there is any limit to how high the capacitance value can be, but it is
always best to do what the manufacturer recommends.
Andrew Lohmann AMIIE
Design Engineer
PLEASE NOTE NEW EMAIL ADDRESS IS:
a...@bellinghamandstanley.co.uk
This communication contains information which is confidential and may also be
privileged. It is for the exclusive use of the addressee. If you are not the
addressee please note that any distribution, reproduction, copying, publication
or use of this communication or the information is prohibited. If you have
received this communication in error, please contact us immediately and also
delete the communication from your computer. We accept no liability for any loss
or damage suffered by any person arising from use of this e-mail.