Datasheet
Data Sheet AD5410/AD5420
Rev. F | Page 29 of 32
INDUSTRIAL, HART COMPATIBLE ANALOG
OUTPUT APPLICATION
Many industrial control applications have requirements for
accurately controlled current output signals, and the AD5410/
AD5420 are ideal for such applications. Figure 55 shows the
AD5410/AD5420 in a circuit design for an output module spe-
cifically for use in an industrial control application. The design
provides for a HART-enabled current output, with the HART
capability provided by the AD5700/AD5700-1 HART modem, the
industry’s lowest power and smallest footprint HART-compliant IC
modem. For additional space-savings, the AD5700-1 offers a 0.5%
precision internal oscillator. The HART_OUT signal from the
AD5700 is attenuated and ac-coupled into the CAP2 pin of the
AD5420. Further information on this configuration can be found
in Application Note AN-1065. An alternative method of coupling
the HART signal into the RSET pin (only applicable of the external
RSET is used), is available in Circuit Note CN-0270. Use of
either configuration results in the AD5700 HART modem output
modulating the 4 mA to 20 mA analog current without affecting
the dc level of the current. This circuit adheres to the HART
physical layer specifications as defined by the HART
Communication Foundation.
The module is powered from a field supply of 24 V. This supplies
AV
DD
directly. For transient overvoltage protection, transient
voltage suppressors (TVS) are placed on both the I
OUT
and field
supply connections. A 24 V TVS is placed on the I
OUT
connection,
and a 36 V TVS is placed on the field supply input. For added
protection, clamping diodes are connected from the I
OUT
pin to the
AV
DD
and GND power supply pins. The recommended external
band-pass filter for the AD5700 HART modem includes a 150 kΩ
resistor, which limits current to a sufficiently low level to adhere
to intrinsic safety requirements. In this case, the input has higher
transient voltage protection and should, therefore, not require
additional protection circuitry, even in the most demanding of
industrial environments.
Isolation between the AD5410/AD5420 and the backplane
circuitry is provided with the ADuM1400 and ADuM1200
iCoupler digital isolators; further information on iCoupler
products is available at www.analog.com. The internally generated
digital power supply of the AD5410/AD5420 powers the field
side of the digital isolators, removing the need to generate a
digital power supply on the field side of the isolation barrier.
The AD5410/AD5420 digital supply out-put supplies up to 5 mA,
which is more than enough to supply the 2.8 mA requirement
of the ADuM1400 and ADuM1200 operating at a logic signal
frequency of up to 1 MHz. To reduce the number of isolators
required, nonessential signals such as CLEAR can be connected
to GND and
FAULT
, and SDO can be left unconnected, reducing
the isolation requirements to just three signals. Doing so,
however, disables the fault alert features of the part.
07027-048
DV
CC
AV
DD
I
OUT
DV
CC
SELECT
CAP1
GNDCAP2
REFOUT REFIN
CLEAR
LATCH
SCLK
SDIN
FAULT
SDO
AD5700/AD5700-1
AD5410/AD5420
10µF
0.1µF
0.1µF
0.1µF
BACKPLANE INTERFACE
BACKPLANE SUPPLY
I
OUT
C3
0.1µF
10kΩ
1µF
150pF
18Ω
+
V
DD1
V
DD2
GND
2
GND
1
V
IA
V
IB
V
OA
V
OB
ADuM1200
V
DD2
GND
1
V
IA
NC
GND
1
V
IC
V
ID
V
IB
V
OA
V
OC
V
OD
V
OB
GND
2
V
E2
GND
2
ADuM1400
V
DD1
MICROCONTROLLER
DIGITAL
OUTPUTS
DIGITAL
INTPUTS
UART
INTERFACE
V
DD2
GND
1
V
IA
V
E1
GND
1
V
OC
V
OC
V
IB
V
OA
V
IC
V
ID
V
OB
GND
2
V
E2
GND
2
ADuM1402
V
DD1
HART_OUT
TXD
RTS
RXD
CD
REF
ADC_IP
V
CC
DGNDAGND
0.1µF
C1
2.2nF
C2
22nF
AV
DD
24V
FIELD
SUPPLY
FIELD
GROUND
SMAJ36CA
36V
150kΩ
1.2MΩ
1.2MΩ
300pF
Figure 55. AD5410/AD5420 in an Industrial Analog Output Application