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Question asked by ABuda on May 22, 2013
Latest reply on May 22, 2013 by ABuda

We're using the ADP3605 on one of our evaluations boards and we need to get a voltage of -5V.


Seeing as our input voltage can go below 5V we're using the circuit shown in Figure 17 of the datasheet to get a scaling factor bigger than -1



However the Vout = (1.5/9.5KOhn)*R1 seems to apply only when the normal circuit is used without the charge pumps.

When using the circuit below with R = 31.6k we get close to -5V, but when we use the circuit above we get -2.6V.



I'll use a potentiometer to see what the resistor needs to be in the meantime, but I'd prefer if I could use a formula to determine an acurrate value.

Is there such a formula or how would I go about deriving one?


Thank you