Micro with 4-independent PWM channels

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I am looking for a PIC or Atmel Micro that has 4-independentl
controlled PWM channels of about 10-bit resolution . The frequnenc
can be the same but I need simultaneous 0-100% duty cycle control o
each channel independently . The max PWM frequncy should be greate
than 1KH
Price Range $2.00-$6.00/usd. A few A/D channels, interrupts,C-Compile
friendly. I have looked @ the PIC18F1220, however , I am not sure o
independent PWM control, as the chip still only has one CCP
Thank
Mik


Re: Micro with 4-independent PWM channels
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A little CPLD does that for you.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

Re: Micro with 4-independent PWM channels

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At 1KHz you could do it in software. perhaps in a seperate (cheap) chip used as
an intelligent
peripheral. I would think an ATTiny26 or PIC16F627 could do it without too much
trouble.

A CPLD like the Xilinx XC9536 could easily do it, and more - cost about $2

 


Re: Micro with 4-independent PWM channels
says...
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I've had this assertion made to me several times.  So far no-one has been
able to back it up.  A CPLD capable of holding 4 10 bit PWMs always seems
to be rather more expensive than a few dollars (You still have to add A/D
micro etc and fit in the $6 range remember).

From what I've seen so far it's always cheaper to add another micro to
act as a PWM peripheral that to add a CPLD to do the same thing.

That's not to say it's impossible, but so far no-ones been able to
demonstrate that it's doable.

Robert

Re: Micro with 4-independent PWM channels
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Agreed.  Why doesn't someone sell a dedicated chip as a PWM expander?
It would be nice to find a SPI or I2C - compatible chip with 6 to 8 PWM
outputs, at least 14 bits, for LED lighting applications.  Preferably in
  a 14 or 16 -pin package, 5V compatible outputs.

All the micros are skimpy on hi-resolution PWM outputs.

mw

Re: Micro with 4-independent PWM channels

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For LED Driving applications Maxim makes a number of ICs which can
directly drive numerous LEDs. The current can be set individually for
each LED. It does not use PWM, so for EMI it is better. Look at
something like the MAX6957AAI, available at Digikey in small
quantities.

Anton Erasmus



Re: Micro with 4-independent PWM channels
snipped-for-privacy@spam.prevent.net says...
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Not so.  Any of the Motorola (Freescale)  micros with a TPU can have
up to 16  high-resolution PWM outputs.   They're a bit big and
expensive to use as a PWM peripheral, though.  ;-)


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Mark Borgerson


Re: Micro with 4-independent PWM channels

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There are zillions of such chips in large scale LED video displays
(the USD 1E6 per display kind).


Best regards,
Spehro Pefhany
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Re: Micro with 4-independent PWM channels
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For LED driving it's so so easy to program allmost any micro to perform this
function. You dont need  dedicated PWM chanells, you can do it in software as
long as the frequency is not too high.

Re: Micro with 4-independent PWM channels
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this
as

I did 48 x 10 bit PWM timers in the FPSLIC once,
using about half of 5000 gates, but then I did not need more...

--
Best Regards,
Ulf Samuelsson
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Re: Micro with 4-independent PWM channels
On Sat, 29 Jan 2005 23:19:00 +0100, "Ulf Samuelsson"

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So I presume, this is now in an appnote ? Can you provide an URL ?

Regards
   Anton Erasmus


Re: Micro with 4-independent PWM channels

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It was done, but the Appnote never got finished. So much to do...

--
Best Regards,
Ulf Samuelsson
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Re: Micro with 4-independent PWM channels
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Sounds intriguing.  What frequency could you run them at?

Robert

Re: Micro with 4-independent PWM channels
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The FPGA portion ran at 25 MHz.
Design was really simple.

A 64 bit x 16 SRAM was implemented in the internal DPRAMs.

10 bits of each word, allocated to an event time.
6 bits allocated to a "timer number".
64 words means that I support 64 timers.

The timers have to be "sorted" according to PWM length..
The shortest PWM length is in position #0 in the SRAM.

The main blocks of the timer is
* A state machine controlling which value should be written to a timer
output..
* A 10 bit counter/comparator connected to the SRAM "event"
* An address register for the SRAM.

In state 1, the address counter counts from 0..47.
The event counter is also started.
The state machine ensures that outputs selected though the "timer number"
in the SRAM are set.

In state 2, the address is reset to zero, addressing word 0.
Any timer output selected here, will be cleared.
The event counter continues to count and will have reached 48 at this point.
When (SRAM.event[adr] == counter), the timer output is cleared
and the address register is incremented to point at the next counter.

There are a few limitations with this.
It is not rail to rail. A PWM output can only be high from 0..(1024-48) so
you lose 5% of the duty cycle.
Two timers cannot change value at the same time.

The end customer thought this was nice, since toggling 48 outputs
simultaneously caused ground bounce.

--
Best Regards
Ulf at atmel dot com
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Re: Micro with 4-independent PWM channels
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So that would be a 25kHz (or so) PWM?

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I can see a few other (non-pwm) potential uses for this type of
structure.

If you ever do write up an appnote it sounds like it would be an
interesting read.


Robert

Re: Micro with 4-independent PWM channels
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They do : try these
http://www.standardproducts.philips.com/products/bitdisplays /

4-16 PWM drives, and also blink...

-jg


Re: Micro with 4-independent PWM channels
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It's not high resolution (only 8 bits), rather slow, and it's really only
two  PWMs mapped to 4-16 outputs.  I can see where it would be useful for
LED displays and even as a pre-driver for controlling coil driven devices
(such as contactors).  I've added it to my interesting devices list.

Robert

Re: Micro with 4-independent PWM channels
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10 bit narrows the field a little.

a) There are many 80C51's with the FX core PCA, which offers 5 channels
of PWM, but at 8 bits. You can expand that to 10, under SW with the
low 1KHz target. ie 8 bits jitter-loaded at 4KHz gives 10 bits @ 1KHz.
  use a fast core and high priority interrupt for the PWM resolution
expansion.

b) For devices with actual HW support, you need to find a PWM with
a SW controlled Counter Reload value, and then you can set the
bit-precision.

  A good device might be the P89LPC932, which has a high-performance
4 channel PWM, all in HW.

c) A PLD could do, but usually you use PLDs only when uC cannot do the
task - ie speed, or some reset/protect operation.
  For a PLD you need 40 bits to store the 4 PWMs, 10 bits to count,
and ideally, prescale and load-buffers, so a 64MC PLD is looking
tight, and 128MC is comfortable.

-jg



Re: Micro with 4-independent PWM channels
Hi,

another point may be worth mentioning. There are 2 more LPC900 devices,
the LPC935 and LPC936 with the same PWM unit (it is called CCU).  All
of these devices are typicaly below $2!!
If you need a 10-bit ADC the LPC938 will fit the bill. I have seen it
in a Philips presentation recently and it is a LPC932 with a 10-bit ADC
and suppossed to be availble within Q1-05

An Schwob

Jim Granville wrote:
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Re: Micro with 4-independent PWM channels
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Maybe one of the new ARM based AT91SAM7S chips should do the job.
You get a 32 kB limited IAR C compiler for free.
AT91SAM7S32 should be witin your price limit

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