AD5422 datasheet(33/38 Pages) AD

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Preliminary Technical Data

AD5412/AD5422

Rev. PrF | Page 33 of 38

APPLICATIONS INFORMATION

DRIVING INDUCTIVE LOADS

When driving inductive or poorly defined loads connect a

0.01µF capacitor between IOUT and GND. This will ensure

stability with loads beyond 50mH. 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 contains ESD protection diodes which

prevent damage from normal handling. The industrial control

environment can, however, subject I/O circuits to much higher

transients. In order to protect the AD5412/AD5422 from

excessively high voltage transients , external power diodes and a

surge current limiting resistor is required, as shown in Figure

64. The constraint on the resistor value is that during normal

operation the output level at IOUT must remain within its

voltage compliance limit of AVDD – 2.5V and the two protection

diodes and resistor must have appropriate power ratings.

Further protection can be provided with Transient Voltage

Suppressors or Transorbs, these are available as both

unidirectional (protects against positive high voltage transients)

and bidirectional (protects 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 are protected.

IOUT

AGND

AVDD

RLOAD

AVDD

AD5412/

AD5422

Figure 64. Output Transient Voltage Protection

SINGLE CONNECTOR FOR IOUT AND VOUT

Typically in analog output modules that facilitate both current

and voltage outputs there is a seperate connector for each

current output and for each voltage output even though either

the voltage output or the current output can be used at any one

time, this results in a redundant connector. For instance in an 8

channel current and voltage output module there will be 16

connectors and only 8 of these will be in use at any one time

resulting in 8 redundant connectors. The AD5412/AD5422 can

be configured with the IOUT and VOUT pins connected together

and to one connector, thus removing the redundant connector

and allowing for a reduced sized connector block. Figure 65

shows that with an external buffer amplifier the

AD5412/AD5422 can be configured with a single output

connector for current and voltage output.

VOUT

IOUT

+VSENSE

-VSENSE

AD5412/

AD5422

IOUT / VOUT

Figure 65. Connecting IOUT and VOUT to one connector

When the AD5412/AD5422 is configured for a voltage output

the IOUT pin will be in tri-state, when configured for a current

output the VOUT pin will be in tri-state, the function of the

buffer is to prevent current leakage to ground through the

+VSENSE pin when the current output is enabled, the +VSENSE pin

is internally connected to AGND through a resistance of

approx. 40kΩ.

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. The

Coupler® family of products from Analog Devices provides

voltage isolation in excess of 2.5 kV. The serial loading structure

of the AD5412/AD5422 make it ideal for isolated interfaces

because the number of interface lines is kept to a minimum.

Figure 66 shows a 4-channel isolated interface to the

AD5412/AD5422 using an ADuM1400. For further

information, visit http://www.analog.com/icouplers.

ENCODE

DECODE

ENCODE

DECODE

ENCODE

DECODE

VIA

VIB

VIC

VOA

VOB

VOC

ENCODE

DECODE

VID

VOD

ADuM1400 *

Controller

Serial Clock Out

Serial Data Out

SYNC Out

Control out

To SCLK

To SDIN

To LATCH

To CLEAR

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 66. Isolated Interface

MICROPROCESSOR INTERFACING

Microprocessor interfacing to the AD5412/AD5422 is via a serial

bus that uses 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.

AD5422 Datasheet(PDF) 33 Page - Analog Devices

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