AD7685ARMZ datasheet(26/29 Pages) AD

26 / 29 page

Data Sheet

AD7685

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 ADuM1402C digital isolator, provides a

compact and high performance solution.

Multiple AD7685s are daisy-chained to reduce the number of

signals to isolate. Note that the SCKOUT, which is a readback of

the AD7685s clock, has a very short skew with the DATA signal.

This skew is the channel-to-channel matching propagation

delay of the digital isolator (tPSKCD). 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.

The complete analog chain runs on a 5 V single 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

VDD1, VE1

GND1

VDD2, VE2

GND2

SCK

CNV

SDI

AD7685

1/4 AD8618

Ω

2V REF

±10V INPUT

5V REF

10µF

100nF

IN– GND

REF VDD VIO

SDO

SCK

CNV

SDI

AD7685

1/4 AD8618

Ω

2V REF

±10V INPUT

5V REF

10µF

100nF

IN– GND

REF VDD VIO

SDO

SCK

CNV

SDI

AD7685

1/4 AD8618

Ω

2V REF

±10V INPUT

5V REF

10µF

100nF

IN–

IN+

GND

REF VDD VIO

SDO

SCK

CNV

SDI

AD7685

1/4 AD8618

Ω

2V REF

Ω

100nF

10µF

5V REF

2V REF

Ω

±10V INPUT

5V REF

10µF

100nF

VIA

VIB

VOC

VOD

VOA

VOB

VIC

VID

2.7V TO 5V

100nF

DATA

SCKOUT

SCKIN

CONVERT

ADuM1402C

OUT

GND

ADR391

Figure 48. A True 16-Bit Isolated Simultaneous Sampling Acquisition System

Rev. D | Page 25 of 28

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