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ADL5304 Dual Supply for 10mA input range

Question asked by csthane on Jun 29, 2018
Latest reply on Jul 5, 2018 by Bruce_H

Hi we are looking to port an old design based on the ADL5304 using a single supply to new design that needs to span a little more current range. This new current range will need to span up to 10mA.

 

On the first page of the datasheet it mentions "Dual-supply operation extends the specified input current range to 10 mA.", however I cannot find much more detail on this other than the datasheet suggesting on p16 recommending the VSMx, DCBI, etc be 0V not 1.5V which makes sense if you need to bias the photo-diode at 0V.

 

However all the performance figures show the device being able to operate to 10mA with Vneg = 0V. Ie in figure 3 it shows 10mA Inum current and Vpos is said to be 5V and Vneg is said to be 0V?

 

In specifications it shows the device being able to work from 1pA to 3mA in single supply mode (Vneg=0), and 1pA to only 1mA in dual supply mode (-5 < Vneg < -2), I am presuming this is a typo and meaning 10mA?

 

Did I miss understand the statement on the front page? In single supply mode I expect 0.2V/dec*log10(10mA/100nA) + 1.5V = 2.5V which is still within the 5V rail and I cannot see any reason a negative supply would be required for this?

 

Mainly I would like to avoid the complexity of a negative supply if possible. Not only would I need to add a negative SMP and possibly LDO, but I would also have to add an additional stage to shift the negative voltage up to the ADC range which will add noise and increases the likelihood of damaging the ADC with reverse voltage.

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