Datasheet

Data Sheet AD5737
Rev. C | Page 43 of 44
INDUSTRIAL HART CAPABLE ANALOG OUTPUT
APPLICATION
Many industrial control applications have requirements for
accurately controlled current output signals, and the AD5737
is ideal for such applications. Figure 65 shows the AD5737 in
a circuit design for a HART-enabled output module, specifically
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 CHARTx
pin of the AD5737. Such a 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.
For transient overvoltage protection, a 24 V transient voltage
suppressor (TVS) is placed on the I
OUT
/V
OUT
connection. For added
protection, clamping diodes are connected from the I
OUT_x
/V
OUT_x
pin to the AV
DD
and GND power supply pins. A 5 kΩ current
limiting resistor is also placed in series with the +V
SENSE_x
input.
This is to limit the current to an acceptable level during a transient
event. 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.
AD5737
10067-065
MCU
UART
INTERFACE
10µF
10kΩ
10µF
0.1µF
0.1µF
0.1µF
0.1µF
2.7V TO 5.5V
DV
DD
AV
DD
RESET
ALERT
FAULT
CLEAR
SYNC
LDAC
SCLK
SDIN
SDO
DGND
AD5700/AD5700-1
TXD
V
CC
RXD
RTS
CD
HART_OUT
+15V
AV
CC
+5V
SW(X4)
V
BOOST
(X4)
IOUT B,C,D
CHART B,C,D
IOUTA
D2
D1
D3
R
P
R
L
REFOUT REFIN CHART A GND
22nF
C1
47nF
C2
4.20mA
CURRENTLOOP
ADC_IP
REF
GND
1µF
150kΩ
150pF
300pF
1.2MQ
1.2MQ
Figure 65. AD5737 in HART Configuration