# ATTiny13 voltage and current ratings

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

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. ### EeyoreGuest

It should be just fine.

Eh ?

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

Graham

3. ### Tim WescottGuest

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 WescottGuest

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. ### ehsjrGuest

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 BettsGuest

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 BettsGuest

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 WescottGuest

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 WescottGuest

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