AD5422 Analog Devices, AD5422 Datasheet - Page 35

• Manufacturer Part Number: AD5422
• Description: Single Channel, 16-Bit, Serial Input, Current Source & Voltage Output DAC
• Manufacturer: Analog Devices

Specifications of AD5422

• Resolution (bits): 16bit
• Dac Update Rate: 40kSPS
• Dac Settling Time: 18µs
• Max Pos Supply (v): +40V
• Single-supply: No
• Dac Type: I or V Out
• Dac Input Format: SPI

APPLICATIONS INFORMATION
DRIVING INDUCTIVE LOADS
When driving inductive or poorly defined loads, connect a
0.01 µF capacitor between I
with loads above 50 mH. There is no maximum capacitance
limit. The capacitive component of the load may cause slower
settling. The digital slew rate control feature may also prove
useful in this situation.
TRANSIENT VOLTAGE PROTECTION
The AD5412/AD5422 contain ESD protection diodes that
prevent damage from normal handling. The industrial control
environment can, however, subject I/O circuits to much higher
transients. To protect the AD5412/AD5422 from excessively
high voltage transients, external power diodes and a surge
current limiting resistor are required, as shown in Figure 73.
The constraint on the resistor value is that, during normal
operation, the output level at I
compliance limit of AV
and resistor must have appropriate power ratings. Further
protection can be provided with transient voltage suppressors or
transorbs; these are available as both unidirectional suppressors
(protect against positive high voltage transients) and
bidirectional suppressors (protect against both positive and
negative high voltage transients) and are available in a wide
range of standoff and breakdown voltage ratings. It is
recommended that all field connected nodes be protected.
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 may occur. The
iCoupler® products from Analog Devices, Inc., provide voltage
isolation in excess of 2.5 kV. The serial loading structure of the
AD5412/AD5422 makes the parts ideal for isolated interfaces
because the number of interface lines is kept to a minimum.
Figure 74 shows a 4-channel isolated interface to the AD5412/
AD5422 using an ADuM1400. For further information, visit
http://www.analog.com/icouplers.
Figure 73. Output Transient Voltage Protection
AD5412/
AD5422
AV
AV
GND
DD
DD
DD
I
OUT
– 2.5 V, and the two protection diodes
OUT
OUT
and GND. This ensures stability
must remain within its voltage
R
P
R
LOAD
Rev. D | Page 35 of 40
MICROPROCESSOR INTERFACING
Microprocessor interfacing to the AD5412/AD5422 is via a serial
bus that uses a protocol compatible with microcontrollers and
DSP processors. The communications channel is a 3-wire
minimum interface consisting of a clock signal, a data signal,
and a latch signal. The AD5412/AD5422 require a 24-bit data-
word with data valid on the rising edge of SCLK.
For all interfaces, the DAC output update is initiated on the
rising edge of LATCH. The contents of the registers can be
read using the readback function.
LAYOUT GUIDELINES
In any circuit where accuracy is important, careful consider-
ation of the power supply and ground return layout helps to
ensure the rated performance. Design the printed circuit board
(PCB) on which the AD5412/AD5422 is mounted so that the
analog and digital sections are separated and confined to
certain areas of the board. If the AD5412/AD5422 is in a system
where multiple devices require an analog ground-to-digital
ground connection, make the connection at one point only.
Establish the star ground point as close as possible to the device.
The AD5412/AD5422 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.
CONTROLLER
1
ADDITIONAL PINS OMITTED FOR CLARITY.
SYNC OUT
DATA OUT
CONTROL
CLOCK IN
SERIAL
SERIAL
OUT
V
V
V
V
IA
IB
IC
ID
Figure 74. Isolated Interface
ENCODE
ENCODE
ENCODE
ENCODE
ADuM1400
1
DECODE
DECODE
DECODE
DECODE
AD5412/AD5422
V
V
V
V
OA
OB
OC
OD
TO
SCLK
TO
SDIN
TO
LATCH
TO
CLEAR