AD1853: output impedance

Document created by analog-archivist Employee on Feb 23, 2016
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Output impedance of AD1853 current output audio DAC
The data sheet for AD1853 specify a couple of things for the analog
outputs, but not the output impedance (it specifies output capacitance).
Would it be possible to obtain that information?


Normally the output impedance of the AD1853 is so high that it can be neglected
and the current output DAC simply looks like a current source. To reach the
specified performance the AD1853 should drive an op-amp I to V converter, as
shown in figure 29 and 30. By driving the virtual earth at the -ve terminal of
the op-amp, the DAC is looking into a very low impedance because the voltage at
the virtual earth hardly changes over the output current range of the DAC.

For some other type of load e.g. a passive load referred to ground, the voltage
at the DAC outputs changes with output current, which causes the specifications
to be degraded, and therefore  the I to V converter is the recommended load.

Also, please ignore the section entiltled Output Drive, Buffering and Loading.
this is a datasheet error and refers to a DAC with voltage output, not current

If you are looking for a DAC with a voltage output, you might wish to consider
the AD1852.