LTSPICE: When using a single power supply, the AD8041 input bias current is too high.

Question

Hi all, 
 
 When using dual power supply, the input bias current is approximately 1.2uA, which is within the normal range.

When powered by a single 5V supply, the input bias current exceeds 16uA, which is beyond the maximum value specified in the datasheet.

Where is the problem?

thanks 
 
 AD8041.asc

retiredEE · Accepted Answer

If you look at the AD8041 model in ADI.lib, you'll find connections of components at the AD8041 inputs (See FrontEnd.asc). All four capacitors tied to the inputs are spec'ed with parallel resistances. When +V and -V are at 5 volts, the bias currents come from I1 and I2 and meet typical spec, but when -V=0 the inputs get additional currents flowing out through the parallel resistances connected to +V making the bias currents approx. -16.8uA. 
 
 FrontEnd.asc)

retiredEE · Answer

I believe you can still use single supplies but keep your reference at Vs/2. That will help keep the bias currents in spec. In the AD8041 part spec, notice those TCP scope traces shown center around Vs/2. The input R/C stage models the Input Characteristic specs. Checkout figures 9 and 13 of the part spec. They're good examples of single supply application.

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LTSPICE: When using a single power supply, the AD8041 input bias current is too high.

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