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'[OT] Re: DAC Conversions..'
1999\02\03@095833 by Heinz Czychun

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Hi Scott,

       I've got an old national data book so I'm not sure the PDF is the same.

       Just a guess from what you've said, and not knowing how you have it
hooked up, is it possible you don't have a negative voltage at pin 3. I
doubt this chip will work with a single power supply.

       Are you using an OPAmp or resistor to convert the current output
into a voltage?

       Or is it possible the chip is "pins up", do you have another to try?

Regards,
Heinz

At 3:31 AM 2/3/99, Scott Shidel... wrote:
>yeah, I have the PDF, and have it hooked up like they do...still cant get
>it to work,,,Rheir diagrams arent really complete though,..they dont hjave
>a complete in cicuit diagram..
<snip>
>>
>> At 10:27 AM 2/2/99, Scott Shidel... wrote:
>> >Can someone point me to a site with some projects for the national
>> >dac0800? I am using one in a project and get get it to give me anything
>> >but 1-1.4v out..its running with a 5v vref...
>> >
<snip>
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1999\02\03@175629 by Scott Shidel...

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On Wed, 3 Feb 1999, Heinz Czychun wrote:

> Hi Scott,
>
>         I've got an old national data book so I'm not sure the PDF is the same
.
>
>         Just a guess from what you've said, and not knowing how you have it
> hooked up, is it possible you don't have a negative voltage at pin 3. I
> doubt this chip will work with a single power supply.
>
Hmmmmm:)
Yah. For power I have +5v and 0v..For a 5v vref, what would you recommend
my voltages be?

>         Are you using an OPAmp or resistor to convert the current output
> into a voltage?
>

Resistor for now.  Only load on the DAC other than the resistor is my
DMM..When I put it into service I am going to use an op amp.

>         Or is it possible the chip is "pins up", do you have another to try?
>
Yeah, I suspected that...chip number 2 is the same way..didnt go for 3:)
I think you have a good point with the power suply voltage..what would you
recommend?

{Quote hidden}

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1999\02\03@194212 by Heinz Czychun

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At 5:54 PM 2/3/99, Scott Shidel... wrote:
>On Wed, 3 Feb 1999, Heinz Czychun wrote:
>
>> Hi Scott,
>>
>>         I've got an old national data book so I'm not sure the PDF is
>>the same.
>>
>>         Just a guess from what you've said, and not knowing how you have it
>> hooked up, is it possible you don't have a negative voltage at pin 3. I
>> doubt this chip will work with a single power supply.
>>
>Hmmmmm:)
>Yah. For power I have +5v and 0v..For a 5v vref, what would you recommend
>my voltages be?

That depends on what voltages are available in the final design.
As a staring point I would suggest a balanced supply starting at some
voltage higher than logic voltage.

For TTL logic the specs. suggest a 10V reference, with a 5k resistor to
provide an IFS of 2ma.

If you then gnd -Io (pin 2) and connect the inverting input of an opamp to
Io (pin 4), the voltage at the output of the opamp will go from 0 to IFS
(2ma) * Rl (Rl being the feedback resistor between the opamp output to the
inverting input). That relationship will hold true, of course, only while
the opamp is in the linear region.

If you just use a resistor at Io you will get a desending voltage starting
at the supply voltage.

{Quote hidden}

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