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help with opamps?

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things

New Member
Hi, well basically we have this DAC AD5668 | Octal, 16-Bit D/A Converter with 5 ppm/°C On-Chip Reference in 16-Lead TSSOP | D/A Converters | Digital to Analog Converters | Analog Devices

Now, with that DAC, we need to somehow get 2 +/-5V differential signals, and then 6 0-5V signals. So what I am wondering, is what would be the best way to get 2 +/-5V differential, and 6 0-5V signals from that DAC chip? We know opamps would be our best bet, but we dont know which opamp would suit us best. Our power supply would be from the USB port, so something that runs on +5V would be good, but if absolutely needed, we can get little DC/DC converters that will give us +/- from the 5V USB ;)

Cheers,
Dan:)
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
I would suggest you're going to struggle unless you use an external power supply, otherwise you will need to generate a -5V supply from the USB +5V one - and USB can only supply a relatively small current.

The other problem is the +5V/-5V swing requirement, even so called 'rail to rail' opamps don't actually manage it, they just get closer than a normal opamp.
 

things

New Member
Hi Nigel, yeah, I am a little worried about the power requirements too. The USB port would basically have to power a FTDI USB - Serial interface, that DAC chip, then some sort of amp. The output signals only really need to be low current.

EDIT: http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=102-1522-ND
I have used that converter for powering opamps from USB power before, it works well, but i'd like to gather idea's first ;)

-Dan ;)
 
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Sceadwian

Banned
What frequency? Rail to rail opamps will deliver rail to rail performance, but their severely slew rate limited at the rail extremes.
 

things

New Member
Well, the galvo's can do about 40K points per second, so around 40Khz.
 

Sceadwian

Banned
I'm guessing a well selected rail to rail opamp would work, you'd have to read the PDF on a couple to determine what the frequency/slew rate limits are at full rail outputs I really don't know if you'll find anything that will give you a full 50khz rail to rail though.

I don't know what kind of signal you're actually driving but a small transformer might work as well, but you'll lose DC coupling and the frequency would have to be fixed or it'd become non-linear.
 

things

New Member
I have got this sorted now, thanks for the help ;)

-Dan :)
 

Sceadwian

Banned
Would you care to explain it to us? We hate it when posters say they got it working the way they want and don't provide details =)
 
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