AVR-Chat

From: "jay marante" <jaythesis@yahoo.com>
To: <AVR-chat@yahoogroups.com>
Sent: Tuesday, April 06, 2004 11:58
Subject: [AVR-Chat] current in MCU and thte sleep mode at
mega16 issue


> just to clear things up...
>
> the datasheet of ATMEGA16L says that DC current Vcc and
GND pins = 200mA. <-- what does this mean?

This means that the total amount of current that is allowed
to enter or leave these pins must not be greater than 200mA.
The part by itself uses very little current, but when you
attach it to things, those things also draw current.
Individually, a small amount, but collectively it can add
up.

> also, what does Icc in power supply current at 8MHz = 20mA
(max) mean?

Current suck on a CMOS part is proportional to its operating
frequency.  In this case, if you clock it at 8 MHz, the part
will draw (nominally) 20 mA.  If you run it at 4 MHz, that
current drops to somewhere around 10 mA.  If you stop it
altogether, it will draw very little current.

> is 200mA means that it is its maximum current that should
be supplied to the MCU?
> and, does 20mA mean that is its normal power consumption?

Yes and yes.

> im using a max883 linear regulator. it is labeled as: 5V,
low-dropout, low-Iq, 200mA Linear regulator.
>    -- Low 220mV dropout voltage at 200mA output current
>    -- 11uA Quiescent current
>
> is this enough to power my system when the input to the
regulator is a 9V alkaline battery? the only device
connected to the MCU is a 4x20 LCD and a 4x3 keypad. i
really need the battery to last long.

If your regulator is adequately heatsinked, then yes it will
work.  But if you want the battery to last long, use a
switching regulator.

> any suggestions? should i change the linear regulator with
a DC-DC converter?

Yes.

> thanks for the help.
>
> -jay

Do you absolutely have to use a 9 volt battery?  (I am
assuming it is the square kind with snaps on the end).  If
not, consider running your project from "AA" or "C" cells.

Erikc  - firewevr@airmail.net
///
"An Fhirinne in aghaidh an tSaoil."
"The Truth against the World."
        -- Bardic Motto

----- Original Message -----
From: "jay marante" <jaythesis@yahoo.com>
To: <AVR-chat@yahoogroups.com>
Sent: Tuesday, April 06, 2004 11:58
Subject: [AVR-Chat] current in MCU and thte sleep mode at
mega16 issue


> just to clear things up...
>
> the datasheet of ATMEGA16L says that DC current Vcc and
GND pins = 200mA. <-- what does this mean?

This means that the total amount of current that is allowed
to enter or leave these pins must not be greater than 200mA.
The part by itself uses very little current, but when you
attach it to things, those things also draw current.
Individually, a small amount, but collectively it can add
up.

> also, what does Icc in power supply current at 8MHz = 20mA
(max) mean?

Current suck on a CMOS part is proportional to its operating
frequency.  In this case, if you clock it at 8 MHz, the part
will draw (nominally) 20 mA.  If you run it at 4 MHz, that
current drops to somewhere around 10 mA.  If you stop it
altogether, it will draw very little current.

> is 200mA means that it is its maximum current that should
be supplied to the MCU?
> and, does 20mA mean that is its normal power consumption?

Yes and yes.

> im using a max883 linear regulator. it is labeled as: 5V,
low-dropout, low-Iq, 200mA Linear regulator.
>    -- Low 220mV dropout voltage at 200mA output current
>    -- 11uA Quiescent current
>
> is this enough to power my system when the input to the
regulator is a 9V alkaline battery? the only device
connected to the MCU is a 4x20 LCD and a 4x3 keypad. i
really need the battery to last long.

If your regulator is adequately heatsinked, then yes it will
work.  But if you want the battery to last long, use a
switching regulator.

> any suggestions? should i change the linear regulator with
a DC-DC converter?

Yes.

> thanks for the help.
>
> -jay

Do you absolutely have to use a 9 volt battery?  (I am
assuming it is the square kind with snaps on the end).  If
not, consider running your project from "AA" or "C" cells.

Erikc  - firewevr@airmail.net
///
"An Fhirinne in aghaidh an tSaoil."
"The Truth against the World."
        -- Bardic Motto



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From: "jay marante" <jaythesis@yahoo.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Wednesday, April 07, 2004 04:29
Subject: Re: [AVR-Chat] current in MCU and thte sleep mode
at mega16 issue


> any suggested DC-DC converter? i prefer from texas
intruments or maxim. they're the only company i can ask for
samples. it should be five volts output.
>
> thanks for the help.
>
> -jay
>

This is the only Maxim part I could find that would be
suitable (i.e. DIP-8 package, minimum external parts, 5.0
volts):

MAX639  (5.0 volts @ 225mA)
http://pdfserv.maxim-ic.com/en/ds/MAX639-MAX653.pdf

For some reason, the Texas Instruments website is not
working right so nothing to offer there.

Erikc  - firewevr@airmail.net
///
"An Fhirinne in aghaidh an tSaoil."
"The Truth against the World."
        -- Bardic Motto

From: "Wagner Lipnharski" <wagner@ustr.net>
To: <AVR-Chat@yahoogroups.com>
Sent: Thursday, April 08, 2004 14:31
Subject: Re: [AVR-Chat] current in MCU and thte sleep mode
at mega16 issue


> erikc wrote:
> > ----- Original Message -----
> > From: "jay marante" <jaythesis@yahoo.com>
> > To: <AVR-Chat@yahoogroups.com>
> > Sent: Wednesday, April 07, 2004 04:29
> > Subject: Re: [AVR-Chat] current in MCU and thte sleep
mode
> > at mega16 issue
> >
> >
> >> any suggested DC-DC converter? i prefer from texas
> > intruments or maxim. they're the only company i can ask
for
> > samples. it should be five volts output.
> >>
> >> thanks for the help.
> >>
> >> -jay
>
>
> If you are using only an AVR with LCD and keyboard, I
guess you don't need
> to have exactly 5V for supply. The AVR stands lower
voltages and also the
> LCD.  Try to find out what is the minimum voltage you
should supply for the
> LCD to work properly. I guess anything above 4.2V will be
ok.  Reducing VCC
> will also reduce AVR current consumption, what extends
battery life.

Reducing the clock frequency also helps since current
consumption is proportional to clock frequency.

> There is a little trick to use LCD and AVR to reduce
current consumption.
>
> It involves to supply the LCD with the minimum possible
voltage, lets say
> 4.2V, then supply the AVR with the same 4.2V but with a
series diode to its
> vcc pin, capacitor to ground.  It reduces VCC to AVR to
around 3.6V.
> If the AVR stands that low voltage, it will run fine and
the logic up level
> of AVR, around 3.6V, will be considered "up" level by the
LCD, so no
> problem.
>
> The main idea is that AVR reduces current consumption with
low VCC, so,
> inserting the diode in series, will also reduce its
overall current
> consumption.

The LCD displays I'm familiar with all need between 4.5 and
5.5 volts to operate correctly.  They also consume very
little current since they run so slowly.  (I think thier
internal clock is something like 200 KHZ or so.)  You can't
reduce the AVR's Vcc below half of the display's Vcc
otherwise the display will not recognise logic high levels
coming from the AVR.  Maybe two or three diodes in series
should be sufficient.

Then going with the switcher's I mentioned earlier, you not
only get more efficient power transfer to the load, but you
can drain the battery to exhaustion as well.


Erikc  - firewevr@airmail.net
///
"An Fhirinne in aghaidh an tSaoil."
"The Truth against the World."
        -- Bardic Motto