AD7846
DIGITAL FEEDTHROUGH
In the preceding interface configurations, most digital inputs to
the AD7846 are directly connected to the microprocessor bus.
Even when the device is not selected, these inputs are constantly
changing. The high frequency logic activity on the bus can feed
through the DAC package capacitance to show up as noise on
the analog output. To minimize this digital feedthrough, isolate
the DAC from the noise source. Figure 29 shows an interface
circuit that isolates the DAC from the bus.
Note that to make use of the AD7846 readback feature using
the isolation technique of Figure 29, the latch needs to be
bidirectional.
A1 TO A15
ADDRESS BUS
ADDRESS
DECODE
CS
MICRO-
PROCESSOR
+5V
CLR
LDAC
R/W
R/W
DIR
G
AD7846*
DATA BUS
B BUS A BUS
D0 TO D15
DB0 TO DB15
2×
74LS245
*LINEAR CIRCUITRY OMITTED FOR CLARITY
Figure 29. AD7846 Interface Circuit Using Latches to Minimize Digital Feedthrough
Rev. G | Page 17 of 24
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