QWe have an +5V/-5V symmetrical supply available. It is therefore possible to
derive +4V from the +5V line. Since the AD8321 requires 9V the following
question arises: Is it possible to connect pins 4,11,12,13,15,16 to -5V and
pins 7,8,9,17,20 to +4V? If digital ground is defined to be -5V, no problem
should occur since the analog inputs and output and pins 5 and 14 are
decoupled by capacitors. Is such an operation acceptable or will the
Is it perhaps even possible to use +5V as Vcc and -5V as GND (in order to
save the +4V regulator), or do 10V supply voltage reduce performance or even
lifetime of the device?
AProvided –5V is defined as digital ground, it is acceptable to operate the
AD8321 with +4V and –5V supplies as you describe. Capacitive coupling on the
input and output as described in figure 25 of the datasheet will ensure the
correct common mode level at the input and output pins of the AD8321.
You must ensure that there is a low impedance return path for the analog ground
return current of the AD8321 back to the power supply. Use of a solid copper
plane for the –5V will be mandatory to ensure best performance. If you have
significant digital circuitry on your board, I would suggest you provide
separate ground return paths for the digital circuit and the AD8321 back to the
The 9V total supply is a thermal limitation of the package. The AD8321 can be
operated from 10V total supply (+/-5V), with no degradation in long term
reliability, provided the following two conditions are met:
1) The maximum ambient temperature is limited to +75degC
2) The total voltage across the AD8321 supply pins is regulated to 10V +/-5%.
This may imply that each
The part is only production tested at 9V total supply. Typical performance will
be similar at 10V total supply, however maximum and minimum gain parameters are
not guaranteed and you can expect the power consumption to increase slightly.