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Author Topic: Problem with LT1639 Op-Amp  (Read 508 times)
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I am using an Arduino to control a DAC which is then used in conjunction with an LT1639 for a gain of 2.4.  The LT1639 is connected to a 24VAC power supply.

When first giving power, the DAC will send 5V to the LT1639 and I should get 12V back from the LT1639, which I do if I have the multimeter connected before power up.  But if I short it to ground or check it after start up it will show a reading of 1.3V until I cycle the power.  What could be causing this?  I already replaced the op-amp once. 

Thanks!
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I emailed LT and this is the response I got

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Are you using a single 24V supply, or +/-12V?  If single supply, then you are probably running into an output swing issue.  On page 4 of the data sheet, the typical output short circuit current is listed as 20mA on a 5V supply.  The Output Saturation Voltage vs Load Current (Output High) graph on page 8 shows the output saturation voltage approaching 1V at 10mA output current so I would not be surprised to see it at 1.3V when the output is shorted and driving 20+mA with a 24V supply.  Can you use a negative rail to allow more headroom and provide a load to limit the current?

I am only using a single 24V supply. 
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