AD7685 Analog Devices, AD7685 Datasheet - Page 25

• Manufacturer Part Number: AD7685
• Manufacturer: Analog Devices

Specifications of AD7685

• Resolution (bits): 16bit
• # Chan: 1
• Sample Rate: 250kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

TRUE 16-BIT ISOLATED APPLICATION EXAMPLE
In applications where high accuracy and isolation are required,
for example, power monitoring, motor control, and some
medical equipment, the circuit given in Figure 48, using the
AD7685 and the
compact and high performance solution.
±10V INPUT
±10V INPUT
±10V INPUT
±10V INPUT
ADuM1402C
2V REF
2V REF
2V REF
2V REF
4kΩ
4kΩ
4kΩ
4kΩ
1/4 AD8618
1/4 AD8618
1/4 AD8618
1/4 AD8618
digital isolator, provides a
1kΩ
1kΩ
1kΩ
1kΩ
5V
5V
5V
5V
5V REF
5V REF
5V REF
5V REF
Figure 48. A True 16-Bit Isolated Simultaneous Sampling Acquisition System
10µF
10µF
10µF
10µF
IN+
IN+
IN+
IN+
REF VDD VIO
REF VDD VIO
REF VDD VIO
REF VDD VIO
IN– GND
IN– GND
IN– GND
IN–
AD7685
AD7685
AD7685
AD7685
GND
SDO
SDO
SDO
SDO
SCK
CNV
SCK
CNV
SCK
CNV
SCK
CNV
SDI
SDI
SDI
SDI
Rev. C | Page 25 of 28
100nF
100nF
100nF
100nF
5V
5V
5V
5V
Multiple AD7685s are daisy-chained to reduce the number of
signals to isolate. Note that the SCKOUT, which is a readback of
the AD7685’s 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
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.
The complete analog chain runs on a 5 V single supply using
the
CMOS
100nF
ADR391
5V
5V
AD8618
IN
ADR391
GND
low dropout reference voltage and the rail-to-rail
V
GND
V
V
V
V
DD1
OUT
OC
OD
IA
IB
amplifier while offering true bipolar input range.
1kΩ
1
, V
E1
10µF
ADuM1402C
1kΩ
1kΩ
5V
100nF
V
DD2
GND
4kΩ
, V
V
V
V
V
5V REF
OA
OB
IC
ID
E2
2V REF
2
DATA
SCKOUT
SCKIN
CONVERT
100nF
PSKCD
2.7V TO 5V
). This allows
AD7685