Datasheet

AD7538
Rev. B | Page 9 of 16
DAC SECTION
Figure 4 shows a simplified circuit diagram for the AD7538
DAC section. The three MSBs of the 14-bit data word are
decoded to drive the seven switches (A to G). The 11 LSBs
of the data word consist of an R-2R ladder operated in a
current steering configuration.
The R-2R ladder current is ⅛ of the total reference input
current. ⅞ current flows in the parallel ladder structure.
Switch A to Switch G steer equally weighted currents between
I
OUT
and AGND.
Because the input resistance at V
REF
is constant, it may be driven
by a voltage source or a current source of positive or negative
polarity.
2R 2R 2R 2R 2R 2R 2R 2R 2R 2R 2R
RR R
R/4
G F E D C B A S10 S9 S0
V
REF
R
FB
I
OUT
AGND
01139-004
Figure 4. Simplified Circuit Diagram for the AD7538 DAC Section