Is a CPLD appropriate for this triple PWM application?

On Fri, 16 Sep 2005 18:39:59 +0200, "Falk Brunner"
<Falk.Brunner@gmx.de> wrote:

>
>"they call me frenchy" <solarfrenchyNO@SPAMhouseofharmonystudios.com>
>schrieb im Newsbeitrag
>
>> Aha, I see.  I will be driving normal L..E..D..s and now that I
>> understand the difference between PWM and PDM, I ask the following
>> question...
>>
>> Since I want to keep system cost to a minimum, I should avoid adding
>> an extra LPF....will PDM work, or should I just stay with PWM?  I will
>> research this tomorrow, but feel free to comment if you like.
>
>For driving LEDs you dont need (and dont should use!) a LPF (low pass
>filter). The filtering is done by the eyes/brain ot the observer. Just keep
>the PWM frequency high enough to avoid flickering (100 Hz ++). The only
>thing you need is the current limiting resistor.
>
>Regards
>Falk
>
>
Right, but my question (as elementary as it may be) was whether PDM
would work for such an application or whether PWM is preferred for any
particular reason.  Both of them seem to acheive the same thing in
different ways assuming the frequency is adequately high.

grusse,
frenchy

"they call me frenchy" <solarfrenchyNO@SPAMhouseofharmonystudios.com>
schrieb im Newsbeitrag

> Right, but my question (as elementary as it may be) was whether PDM
> would work for such an application or whether PWM is preferred for any
> particular reason.  Both of them seem to acheive the same thing in
> different ways assuming the frequency is adequately high.

For LEDs, PWM is just as good as PDM. PDM has the advantage that you can use
lower clock frequencies, but this is not a real advantage.

Regards
Falk

they call me frenchy wrote:
<snip>

> I appreciate your input.  You will probably hear from me again in the
> coming weeks.  BTW, what is the most appropriate newsgroup for my new
> uC path?
> 
> infinite gratitude,
> frenchy

That would be comp.arch.embedded.  If you go for the AVR, you'll also 
find www.avrfreaks.net to be very helpful.

mvh.,

David

On Fri, 16 Sep 2005 23:06:05 +0200, "Falk Brunner"
<Falk.Brunner@gmx.de> wrote:

>For LEDs, PWM is just as good as PDM. PDM has the advantage that you can use
>lower clock frequencies, but this is not a real advantage.
>
>Regards
>Falk
>
>

In battery powered applications I was under the impression that
lowering the clock frequency was one of the main keys to saving
precious power.  Also, the fact that PDM uses less logic resources
than does PWM further tells me that PDM has an edge over PWM for
L..E..D applications.... but I see that most driver ICs for this this
application use PWM pretty much exclusively, hmmmm.

thx,
frenchy

they call me frenchy wrote:
> On Fri, 16 Sep 2005 23:06:05 +0200, "Falk Brunner"
> <Falk.Brunner@gmx.de> wrote:
> 
> 
>>For LEDs, PWM is just as good as PDM. PDM has the advantage that you can use
>>lower clock frequencies, but this is not a real advantage.
>>
>>Regards
>>Falk
>>
> In battery powered applications I was under the impression that
> lowering the clock frequency was one of the main keys to saving
> precious power.  Also, the fact that PDM uses less logic resources
> than does PWM further tells me that PDM has an edge over PWM for
> L..E..D applications.... but I see that most driver ICs for this this
> application use PWM pretty much exclusively, hmmmm.

  A minus of PDM, is there are more edges, and thus more EMC issues....

  Because Microcontrollers target wider markets, and have timers
with capture/compare from way back, they almost all use PWM.
  In terms of uC die area, the difference is not significant.
  However, (just to keep you on your toes), a few use a mix of PWM
and PDM, and we have done a design that used a UART to
generate PWM+PDM DAC output.


-jg