JAJSSV2G March 2011 – January 2024 DAC3482
PRODUCTION DATA
The CMOS DACs consist of a segmented array of PMOS current sources, capable of sourcing a full-scale output current up to 30mA. Differential current switches direct the current to either one of the complementary output nodes IOUTP or IOUTN. Complementary output currents enable differential operation, thus canceling out common mode noise sources (digital feed-through, on-chip and PCB noise), dc offsets, even order distortion components, and increasing signal output power by a factor of two.
The full-scale output current is set using external resistor RBIAS in combination with an on-chip bandgap voltage reference source (1.2V) and control amplifier. Current IBIAS through resistor RBIAS is mirrored internally to provide a maximum full-scale output current equal to 64 times IBIAS.
The relation between IOUTP and IOUTN can be expressed as:
We will denote current flowing into a node as – current and current flowing out of a node as + current. Since the output stage is a current source the current flows from the IOUTP and IOUTN pins. The output current flow in each pin driving a resistive load can be expressed as:
where CODE is the decimal representation of the DAC data input word
For the case where IOUTP and IOUTN drive resistor loads RL directly, this translates into single-ended voltages at IOUTP and IOUTN:
Assuming that the data is full scale (65535 in offset binary notation) and the RL is 25Ω, the differential voltage between pins IOUTP and IOUTN can be expressed as:
Note that care should be taken not to exceed the compliance voltages at node IOUTP and IOUTN, which would lead to increased signal distortion.