Connect with us

ATTiny13 voltage and current ratings

Discussion in 'Electronic Basics' started by [email protected], Jul 3, 2007.

Scroll to continue with content
  1. Guest

    I was reading the datasheet on my ATTiny13, and noticed the following
    ABSOLUTE MAXIMUM ratings:

    Maximum Operating Voltage 6.0V
    DC Current Vcc and GND pins: 200 mA

    I was planning on powering my device with 4 1.2 NiMH batteries. Do I
    still need a 78L05 voltage regulator, or can I skip that? (I've got
    one just in case, but wondering if it's necessary with 4.8V
    nominal...)

    Why the restriction on the DC current input? Won't the device just
    suck as much current as it needs? Or should I put a resistor there in
    series with Vcc...? R=V/I = 5.0V / 0.2A = 25 ohms?

    Thanks,

    Michael
     
  2. Eeyore

    Eeyore Guest

    It should be just fine.

    Eh ?

    It means you can't exceed that current on those pins *including any load
    currents*.

    Graham
     
  3. Tim Wescott

    Tim Wescott Guest

    NiMH batteries will routinely show 1.25V/cell when they are fully
    charged, which puts you right at 6V. 1.3V/cell is not unheard of, and
    that puts you over. I'd recommend a low drop out* 5V regulator. Even
    if you could just go straight off the battery you want to have some
    healthy capacitance on the power supply line, as batteries have
    significant internal resistance that can cause supply-line droop, which
    messes up the processor.

    The DC current input restriction is there because something in the chip
    will burn up if you exceed it. The chip by itself shouldn't consume
    much power (the amount will be in the data sheet), but you will be
    driving things from it's output pins -- the maximum current directive is
    to you, the circuit designer, to make sure you don't hang too many
    things off of the chip.

    * The 78L05 needs more than 1.5V of overhead, depending on whose you
    buy and how much current you pull -- I figure that 8V into the regulator
    is the minimum safe value, and I prefer 9V.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  4. Guest



    Thanks for the useful information. I'll look more into the specs on
    my 78L05.

    Say... you wrote "Applied Control Theory for Embedded Systems", eh?
    Are Ziegler-Nichols and Cohen-Coon covered in your text?

    Thanks,

    Michael
     
  5. Tim Wescott

    Tim Wescott Guest

    No, but if I ever get a chance to do some addenda, Z-N is on my list of
    things to add, and now I'm going to have to familiarize myself with
    Cohen-Coon.

    Ziegler-Nichols tuning tends to result in an underdamped system; Astrom
    and Hagglund improved on this in a way that uses the Z-N measurements
    followed by different calculations.

    If you can get your hands on the system for long enough, it's much
    better to do a more formal system identification, followed by a
    controller design. This covers a lot more bases than Z-N tuning does.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  6. ehsjr

    ehsjr Guest

    Forget the 78L05 or any other regulator. You don't need it,
    and it won't work, in any event.

    You have 4 cells. The maximum voltage per cell is 1.43. So
    the maximum total voltage is 5.72, and your device can handle
    up to 6.00. The cells will drop to nominal very quickly, so
    you'll have 4.8 volts. No 5 volt regulator will work with 4.8 V
    input.

    If you *must* have 5.0 volts exactly, you'll either need to
    add more cells and a regulator, or use a dc-dc converter, which
    *can* produce 5V regulated output with 4.8V input.

    Ed
     
  7. Guest


    I could use a 9V batt. Don't like to, but I could.

    I suppose I could even go to Goodwill, get some wall warts for $1, and
    use a regulator on that.

    I just have a house full of 1.2V NiMHs.
     
  8. Guest


    I took a process control class in college; didn't learn much from it,
    I'm afraid, and I didn't do so great in the class first time around
    (wink) - but those terms came up during class (PID controllers,
    etc.)

    Personally, during class, I wondered why a simple on-off thermostat
    couldn't work. I just couldn't visualize the need for such esoteric
    mathematical exercises for control.

    If Z-N and Cohen-Coon have been superseded by something even better,
    I'm all ears...

    Michael
     
  9. Jasen Betts

    Jasen Betts Guest

    If you're going to charge the battery while the controller is
    connected, or if you want to protect it against misuse then the regulator
    would be needed, but otherwise no.
    if you put large loads on the output pins those currents flow through VCC or
    GND

    Bye.
    Jasen
     
  10. Jasen Betts

    Jasen Betts Guest

    What is it with arithmetic this week? everyone seems to be messing it
    up!

    anything less than 1.5v per cell is OK.
     
  11. Tim Wescott

    Tim Wescott Guest

    Often a simpler approach _is_ all that's needed -- witness the millions
    of homes with on-off thermostats that keep the temperature nice and
    comfortable.

    But then, often that simpler approach has its limitations -- witness the
    millions of homes that use continuously-variable heat pumps with fancy
    "thermostats", that keep the temperature nice and comfortable _and_ save
    a considerable amount of power over a heat pump with an on-off thermostat.

    On-off control also forces the process variable to oscillate around some
    value (hopefully the right one). If this isn't tolerable, then you need
    continuous control.

    And if you want to know ahead of time if on-off control is adequate, you
    need to do at least some of that fancy math.
    Entire books have been written on self-tuning PID controllers.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  12. Tim Wescott

    Tim Wescott Guest

    Oh gawd. (4)(1.25) = 5. Not six. Ooh I hate it when I carry twice.

    Ehsjr is right -- you don't need a regulator. Just put a honkin' big
    cap on the output, and have fun.

    Make sure the processor will still be happy when you get down to
    0.9V/cell, though -- anything more and the battery still has lots of
    useful charge. You should also consider shutting your system off
    automatically when the voltage drops to that level, to save the battery
    from damage.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Do you need to implement control loops in software?
    "Applied Control Theory for Embedded Systems" gives you just what it says.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-