Datasheet

AD7686
Rev. B | Page 24 of 28
TRUE 16-BIT ISOLATED APPLICATION EXAMPLE
In applications where high accuracy and isolation are required,
such as power monitoring, motor control, and some medical
equipment, the circuit shown in
Figure 47, using the AD7686
and the
ADuM1402C digital isolator, provides a compact and
high performance solution.
Multiple AD7686 devices are daisy-chained to reduce the
number of signals to isolate. Note that the SCKOUT, which is a
readback of the AD7686 clock, has a very short skew with the
DATA signal.
This skew is the channel-to-channel matching propagation
delay of the digital isolator (t
PSKCD
). This allows running the
serial interface at the maximum speed of the digital isolator
(45 Mbps for the
ADuM1402C), which would have been
otherwise limited by the cascade of the propagation delays of
the digital isolator. For instance, four AD7686 devices running
at 330 kSPS can be chained together.
The complete analog chain runs on a single 5 V supply using
the
ADR391 low dropout reference voltage and the rail-to-rail
CMOS
AD8618 amplifier while offering true bipolar input range.
IN– GND
REF VDD
VIO
SDO
V
DD1
, V
E1
GND
1
V
DD2
, V
E2
GND
2
SCK
CNV
SDI
AD7686
1/4 AD8618
5V
1kΩ
2V REF
±10V INPUT
5V REF 5V
5V
10µF 100nF
100nF
IN– GND
REF VDD
VIO
SDO
SCK
CNV
SDI
AD7686
1/4 AD8618
5V
1kΩ
2V REF
±10V INPUT
5V REF 5V
10µF 100nF
IN– GND
REF VDD
VIO
SDO
SCK
CNV
SDI
AD7686
1/4 AD8618
5V
1kΩ
2V REF
±10V INPUT
5V REF 5V
10µF 100nF
IN–
IN+
IN+
IN+
IN+
GND
REF VDD
VIO
SDO
SCK
CNV
SDI
AD7686
1/4 AD8618
5V
1kΩ4kΩ
4kΩ
4kΩ
4kΩ
2V REF
5V
5V
1kΩ1kΩ
1kΩ
100nF10μF
5V REF
2V REF
4kΩ
±10V INPUT
5V REF 5V
10µF 100nF
V
IA
V
IB
V
OC
V
OD
V
OA
V
OB
V
IC
V
ID
2.7V TO 5V
100nF
DATA
SCKOUT
SCKIN
CONVERT
ADuM1402C
OUT
GND
IN
ADR391
02969-048
Figure 47. A True 16-Bit Isolated Simultaneous Sampling Acquisition System