about AD8304 VNEG current

Question

Hi 
 When using the AD8304 with VNEG and ACOM separated (e.g., ACOM=0V, VNEG=-0.5V, VPS=5V), if the input current to INPT is 1mA, what kind of driving capability is required for VNEG? In other words, what is the maximum current for VNEG?

enash · Accepted Answer

The photodiode current will flow out of the VNEG pin and into your negative supply. So if you plan to have photodiode currents as high as 10mA, you the supply will have to sink that. The datasheet also says “The bias current, buffer output (and its load) current, and the full IPD all have to be absorbed by this negative supply, and its supply capacity must be ensured for the maximum current condition”. It's unclear how much current all this adds up to. We know that the part has a total quiescent current of 4.5mA. All of this current is not going through VNEG. But without knowing more, I would suggest that you provide a VNEG that can sink 15mA.)

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