AD5532
Rev. D | Page 19 of 20
Typical Application Circuit (ISHA Mode)
The AD5532 can be used to set up voltage levels on 32 channels
as shown in the circuit that follows. An AD780 provides the 3 V
reference for the AD5532 and for the AD5541 16-bit DAC. A
simple 3-wire interface is used to write to the AD5541. Because
the AD5541 has an output resistance of 6.25 k
Ω(typ), the time
taken to charge/discharge the capacitance at the V
IN
pin is
significant. Hence an AD820 is used to buffer the DAC output.
Note that it is important to minimize noise on V
IN
and REFIN
when laying out the circuit.
00939-C-027
AD5532*
OFFS_IN
OFFS_OUT
REFIN
V
IN
SCLK DIN SYNC
AV
CC
DV
CC
V
OUT
0–V
OUT
31
V
SS
V
DD
AD820
CS
DIN
SCLK
*ADDITIONAL PINS OMITTED FOR CLARITY
AD780*
V
OUT
AD5541*
REF
AV
CC
Figure 28. Typical Application Circuit (ISHA Mode)
POWER SUPPLY DECOUPLING
In any circuit where accuracy is important, careful
consideration of the power supply and ground return layout
helps to ensure the rated performance. The printed circuit
board on which the AD5532 is mounted should be designed so
that the analog and digital sections are separated and confined
to certain areas of the board. If the AD5532 is in a system where
multiple devices require an AGND-to-DGND connection, the
connection should be made at one point only. The star ground
point should be established as close as possible to the device.
For supplies with multiple pins (V
SS
, V
DD
, AV
CC
) it is recom-
mended to tie those pins together. The AD5532 should have
ample supply bypassing of 10 μF in parallel with 0.1 μF on each
supply located as close to the package as possible, ideally right
up against the device. The 10 μF capacitors are the tantalum
bead type. The 0.1 μF capacitor should have low effective series
resistance (ESR) and effective series inductance (ESI), such as
the common ceramic types that provide a low impedance path
to ground at high frequencies, to handle transient currents due
to internal logic switching.
The power supply lines of the AD5532 should use as large a
trace as possible to provide low impedance paths and reduce the
effects of glitches on the power supply line. Fast switching
signals, such as clocks, should be shielded with digital ground
to avoid radiating noise to other parts of the board and should
never be run near the reference inputs. A ground line routed
between the D
IN
and SCLK lines helps reduce crosstalk between
them (not required on a multilayer board as there is a separate
ground plane, but separating the lines helps).
Note it is essential to minimize noise on V
IN
and REFIN lines.
Particularly for optimum ISHA performance, the V
IN
line must
be kept noise free. Depending on the noise performance of the
board, a noise filtering capacitor may be required on the V
IN
line. If this capacitor is necessary, then for optimum throughput
it may be necessary to buffer the source which is driving V
IN
.
Avoid crossover of digital and analog signals. Traces on
opposite sides of the board should run at right angles to each
other. This reduces the effects of feedthrough through the
board. A micro-strip technique is by far the best, but not always
possible with a double-sided board. In this technique, the
component side of the board is dedicated to ground plane while
signal traces are placed on the solder side.
As is the case for all thin packages, care must be taken to avoid
flexing the package and to avoid a point load on the surface of
the package during the assembly process.
