AD5755-1x AD [Analog Devices], AD5755-1x Datasheet - Page 33

• Manufacturer Part Number: AD5755-1x
• Description: Quad Channel, 16-Bit, Serial Input, 4-20mA & Voltage Output DAC, Dynamic Power Control, HART Connectivity
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
The AD5755-1 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 low
effective series inductance (ESI) such as the common ceramic
types, which 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 AD5755-1 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 SDIN and SCLK lines helps reduce crosstalk
between them (not required on a multilayer board that has a
separate ground plane, but separating the lines helps). It is
essential to minimize noise on the REFIN line because it
couples through to the DAC output.
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 feed through the board. A
microstrip technique is by far the best, but not always possible
with a double-sided board. In this technique, the component
Rev. PrD | Page 33 of 34
side of the board is dedicated to ground plane, while signal
traces are placed on the solder side.
GALVANICALLY ISOLATED INTERFACE
In many process control applications, it is necessary to provide
an isolation barrier between the controller and the unit being
controlled to protect and isolate the controlling circuitry from
any hazardous common-mode voltages that might occur.
Isocouplers provide voltage isolation in excess of 2.5 kV. The
serial loading structure of the AD5755-1 makes it ideal for
isolated interfaces, because the number of interface lines is kept
to a minimum. Figure 23 shows a 4-channel isolated interface
to the AD5755-1 using an ADuM1400. For more information,
go to www.analog.com.
1
ADDITIONAL PINS OMITTED FOR CLARITY
SERIAL CLOCK OUT
µCONTROLLER
SERIAL DATA OUT
CONTROL OUT
SYNC OUT
V
V
V
V
IA
IB
IC
ID
ADuM1400
Figure 23. Isolated Interface
ENCODE
ENCODE
ENCODE
ENCODE
1
DECODE
DECODE
DECODE
DECODE
AD5755-1
V
V
V
V
OA
OB
OC
OD
TO SCLK
TO SDIN
TO SYNC
TO LDAC