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Discussion in 'Electronic Design' started by Bob Stephens, Apr 27, 2004.

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  1. Bob Stephens

    Bob Stephens Guest

    I am currently using a Silicon Labs (Cygnal) 8051 derivative -C8051F060 -
    in an prototype embedded design. I am looking for a replacement device for
    future revisions which would have most or all of the following:

    8 or 16 bit architecture
    4 or more 8 bit +/- 25 mA ports
    2 16 bit 1 Msps A/D
    2 or more 10 bit 200 Ksps A/D
    2 12 bit DAC
    2 USART
    I2C
    SPI
    4 or more counter/timers
    Low power modes w/wakeup via USART interrupt
    Good C/Assembler development tools and debugger
    JTAG programming interface
    Readily available silicon through distributors in prototype and production
    quantities
    Datasheets which approximate the actual performance of the device

    Anyone have any particular favorites they've had good luck with?


    TIA

    Bob
     
  2. This looks like a trick question - what's the F060 missing from the
    list above ?

    16 bit / 1MSPS ADCs in uC are not common things, but you can get
    some DSPs with more MSPS and fewer bits.

    -jg
     
  3. If you can put all the analog stuff outside
    (could be hard to get high speed 16 bit ADC in a micro)
    then the AT91RM3400 could be good for the job.

    32 bit ARM7 at 66 MHz executing from internal SRAM, loading from ext
    dataflash
    Multiple I/O
    5 x USART
    SPI
    TWI (I2C compatible)
    6 timers
    low power

    The AT91SAM7A3 will be the flash version of above with some 10 bit ADC.
     
  4. mikem

    mikem Guest

    Good Luck!
     
  5. Bob Stephens

    Bob Stephens Guest

    Primarily the low power consumption and accurate specs...
     
  6. Bob Stephens

    Bob Stephens Guest

    Yes, I am considering using an outboard ADC. Unfortunately real estate is
    at a premium - as usual.

    Bob
     
  7. Bob Stephens

    Bob Stephens Guest

    Actually, the Cygnal part (in *Theory*) provides all of these features and
    more. If only they were a wee bit more honest in their datasheets...


    Bob
     
  8. Actually, the Cygnal part (in *Theory*) provides all of these features and
    I'm working a lot with Cygnal devices and I'm curious what did you mean by
    "If only they were a wee bit more honest in their datasheets..." ?

    - Dejan
     
  9. rickman

    rickman Guest

    Like the others have said, trying to get a 1 MSPS 16 bit ADC in an MCU
    is pretty much like looking for a one legged relay runner. 16 bit ADC
    chips in the MSPS range are difficult to make and tend to be a bit
    pricey by themselves, I have seen $10 to $30 each depending on INL. To
    put two of them in an MCU and keep the total price below $50 would be a
    trick.

    I am sure you can find all the other features in various MCUs. Check
    out the ADI AD7655 and similar parts. I think this TQFP48 is about as
    small as you will get. But realize that you won't get 1 MSPS at "low
    power". I'm not sure what your issues with the Cygnal part are. I am
    sure people here would be interested in the details.

    --

    Rick "rickman" Collins


    Ignore the reply address. To email me use the above address with the XY
    removed.

    Arius - A Signal Processing Solutions Company
    Specializing in DSP and FPGA design URL http://www.arius.com
    4 King Ave 301-682-7772 Voice
    Frederick, MD 21701-3110 301-682-7666 FAX
     
  10. Bob Stephens

    Bob Stephens Guest

    The only Cygnal part I have used is the '060 - I can't speak to the rest.
    The data sheet specs as regards power consumption, and internal Vref
    performance are extremely misleading at best. We are using it in a battery
    powered device, and with the analog peripherals running it is an extreme
    power hog. Vdd typical with CPU active is stated as 18 mA, "Power supply
    Current (each ADC)is given as 4.0 mA typical. Well, I'm measuring around
    85mA total for Vdd and AVdd with one converter running. Also "The
    independent, temperature stable 1.25 V bandgap voltage reference generator,
    with an output buffer amplifier which multiplies the bandgap reference by
    2" comes in at about 2.4401 volts except when it's warm or cold or ... and
    varies from device to device. I've had to add an external precision Vref to
    get any kind of stability out of the converters - not a big deal if planned
    up front but a thumping PITA to tack on to a densely packed board after the
    fact.
     
  11. Jeff Fox

    Jeff Fox Guest

    What do you consider to be misleading in the datasheets? Peak
    advertizing mips for artificial problems? That is pretty much
    common practice. Or is it something else?
     
  12. Cygnal are at the low end of uA/MHz, so good luck.
    Also, I've never seen a data sheet that could not be improved :)
    -jg
     
  13. Bob Stephens

    Bob Stephens Guest

    <repost of reply to yet another post>

    The only Cygnal part I have used is the '060 - I can't speak to the rest.
    The data sheet specs as regards power consumption, and internal Vref
    performance are extremely misleading at best. We are using it in a battery
    powered device, and with the analog peripherals running it is an extreme
    power hog. Vdd typical with CPU active is stated as 18 mA, "Power supply
    Current (each ADC)is given as 4.0 mA typical. Well, I'm measuring around
    85mA total for Vdd and AVdd with one converter running. Also "The
    independent, temperature stable 1.25 V bandgap voltage reference generator,
    with an output buffer amplifier which multiplies the bandgap reference by
    2" comes in at about 2.4401 volts except when it's warm or cold or ... and
    varies from device to device. I've had to add an external precision Vref to
    get any kind of stability out of the converters - not a big deal if planned
    up front but a thumping PITA to tack on to a densely packed board after the
    fact.
     
  14. rickman

    rickman Guest

    That is sad to hear. I have not used any of the Cygnal parts, but I had
    the impression from others that they were solid, well designed parts.
    If you are seeing these problems over a batch of parts, is it possible
    that they were not made well? Often internal parameters are not tested
    and it is assumed that if the rest of the chip is good, then these
    parameters should be good "by design". You might want to contact Cygnal
    about it.

    One part that I know I have heard good things about on the analog side
    is the MSP430 family. They are not 5 volt tolerant, but they seem to
    come with a wide variety of peripherals and can run on very, very low
    Idd. If you can deal with a 3.3 volt part on your board, this might be
    a better choice.

    --

    Rick "rickman" Collins


    Ignore the reply address. To email me use the above address with the XY
    removed.

    Arius - A Signal Processing Solutions Company
    Specializing in DSP and FPGA design URL http://www.arius.com
    4 King Ave 301-682-7772 Voice
    Frederick, MD 21701-3110 301-682-7666 FAX
     
  15. Bob Stephens

    Bob Stephens Guest

    Actually, my board is 3.3V. Thanks Rick, I'll take a look at the MSP.
     
  16. That sounds Atypical - you have, of course, asked Cygnal about it ?

    Vref stability is a matter for the fine print. ALL Vrefs will differ
    from unit to unit, and also vary over temperature.
    The key point is, by how much ?

    [They quote 2.44V, or 2.43V Typical as Vref, so 'about 2.4401' does not
    sound too terrible ? ]

    Their spec also says typ 15ppm/'C tempco.
    That's not the very best, but Maxim sell plenty of Vrefs worse than
    that. Remember this is an ON-CHIP, Vref.

    'Best in class' on External Vrefs approaches a few ppm, but they will
    cost as much as the smaller uC :)
    If the tempco matters, you'd probably also want to do better
    than the 1.25% Vref tolerance.
    eg : Maxim can give Vref's with 3ppm and 0.04% Cals.


    The Icc numbers sound 'way out' - did you check their EVB Icc, and a
    number of samples ?
    What did Cygnal say ?

    I have not used their 060, but their 330 came in right where expected
    on Icc.

    -jg
     
  17. An on-chip Vref has the disadvantage that it is at the die temperature
    for the micro. No big deal if the micro is running at a couple of mA
    and not switching much, but if it is running hot you can get
    objectionable (perhaps on cosmetic grounds) drift during warm-up.

    Best regards,
    Spehro Pefhany
     
  18. Ben Bradley

    Ben Bradley Guest

    In sci.electronics.design,comp.arch.embedded, Bob Stephens
    ^^^^^^^

    <SOAPBOX,MODE="ON">

    <ahem>

    DO NOT DESIGN WITH "TYPICAL" VALUES.

    Every chip can be at the stated minimum or maximum (whichver is
    worst case) and still be within spec. If they don't have a max current
    or power condumption spec, then that's bad, because it can pull five
    amperes and (as long as everything else functions within guaranteed
    specs) still be "within spec."
    If there is some minumum or maximum spec that the chip isn't
    meeting (as long as there's no asterisk where it says "these are just
    approximate, we don't guarantee them" or other such weasel words),
    then you can call the manufacturer and say they have defective parts,
    and reasonably ask that they be replaced.
    OTOH, every data sheet says specs 'may change at any time' so they
    might just change the specs when you complain, but if any
    manudfacturer did things like that there would be a LOT of people
    complaining about it on Usenet and elsewhere,

    Bob Pease has given this lecture at least once, I forget if it was
    in his ED column or 'live' as part of is National tour ... ISTR he
    suggested running white-out down the 'typical' column of data sheets -
    regardless, that's a good idea.
     
  19. Bob Stephens

    Bob Stephens Guest

    What you say is of course true. The problem in this case is that the
    "datasheet" is over 300 pages long and contradicts itself all over the
    place and as regards maximum and minimum specs the most common value for
    this part is "TBD"...

    Bob

    <SOAPBOX_MODE &= 0x00;> //you forgot to turn it off
     
  20. Fred Bartoli

    Fred Bartoli Guest


    If you have a power hungry uC and plenty of unused CPU time then you have
    die temperature control for (almost) free.


    Fred.
     
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