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ADL5315 interfacing with AD8304 - IOUT Voltage Compliance

Question asked by ICHIBAN on Apr 2, 2018
Latest reply on Apr 3, 2018 by jdobler

Hi, I am using a ADL5315 high side current mirror to measure photodiode dark currents across a range of bias levels. I am looking at characterizing them from 0 - 6.5V DC. I have a DAC that will set the voltage on VSET (not connected to SREF) and am using a 7.5V LDO on VPOS. The datasheet notes that the voltage on the IOUT pin can be anywhere from 0 to (Vpos -1V), which would limit my DAC swing to 6.5V in my case. I am monitoring the currents using the AD8304 current to voltage log amplifier.


Now, given that the AD8304 has a max supply voltage of 5.5V, I suspect that the potential 6.5V on the INPT pin will cause issues. Can someone confirm this? The absolute maximum VCC limit listed is 8V and no voltage compliance is listed on this pin. It only lists a 0.5V node voltage which will be over-driven depending on the value of IOUT of the ADL5315.


I would recommend making this fully clear to the designer in the AN-1512 app note. Connecting the two chips will only work under certain configurations. 


Else, are there any other current to voltage log detectors that would be suitable for upwards of 8V applied to the INPT pin? 


Thanks in advance.