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Old 20th April 2011, 12:18 PM   #1
Gunders is offline Gunders  Norway
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Default Problems understanding I/V converter from DAC

Hi
I'm trying to understand the I/V converter used in this schematic. I have a problem seeing why they have connected the non-inverting input to the inverting output from the DAC instead of grounding it. Do they achieve anything by doing this? I also wonder why they use an I/V converter when it is a voltage output DAC.

Datasheet for the MAX5184 DAC: http://datasheets.maxim-ic.com/en/ds...81-MAX5184.pdf

Thank you for your help in advance
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Old 20th April 2011, 12:32 PM   #2
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What makes you think this is an I/V converter? Looks to me like a poor implementation of a differential amp.
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Old 25th April 2011, 10:15 PM   #3
DF96 is offline DF96  England
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Are they using the opamp as a unity gain buffer, with some frequency compensation to keep it stable? Just a guess, as I am not familiar with either chip.
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Old 25th April 2011, 11:10 PM   #4
cbdb is offline cbdb  Canada
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Its an I/V converter. No current into the opamp inputs so Vout =Iin- x (R19//C129) , or Iin- x 3.3k till the caps impedance reaches 3.3k then Vout drops,(low pass filter). Someone else can do the math.

Last edited by cbdb; 25th April 2011 at 11:12 PM.
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Old 26th April 2011, 12:04 AM   #5
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Quote:
Originally Posted by Gunders View Post
Hi
I'm trying to understand the I/V converter used in this schematic. I have a problem seeing why they have connected the non-inverting input to the inverting output from the DAC instead of grounding it. Do they achieve anything by doing this? I also wonder why they use an I/V converter when it is a voltage output DAC.

Datasheet for the MAX5184 DAC: http://datasheets.maxim-ic.com/en/ds...81-MAX5184.pdf

Thank you for your help in advance
The spec sheet says the MAX5184 has 400 ohm internal load resistors on the current outputs, so the chip's outputs are already "voltage". The opamp is simply a buffer with some gain.

Bobby Dipole
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Old 26th April 2011, 12:12 AM   #6
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Looks like a regular I/V converter. Maybe they tie the plus input of the op amp to their internal ground to insure accuracy.

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