AD7708 datasheet(36/44 Pages) AD

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AD7708/AD7718

AD7708/AD7718-to-ADSP-2103/ADSP-2105 Interface

Figure 21 shows an interface between the AD7708/AD7718 and

the ADSP-2103/ADSP-2105 DSP processor. In the interface

shown, the RDY bit of the Status Register is again monitored to

determine when the Data Register is updated. The alternative

scheme is to use an interrupt-driven system, in which case the

RDY output is connected to the IRQ2 input of the ADSP-2103/

ADSP-2105. The serial interface of the ADSP-2103/ADSP-2105

is set up for alternate framing mode. The

RFS and TFS pins of

the ADSP-2103/ADSP-2105 are configured as active low outputs

and the ADSP-2103/ADSP-2105 serial clock line, SCLK, is also

configured as an output. The

CS for the AD7708/AD7718 is

active when either the

RFS or TFS outputs from the ADSP-2103/

ADSP-2105 are active. The serial clock rate on the ADSP-

2103/ADSP-2105 should be limited to 3 MHz to ensure correct

operation with the AD7708/AD7718.

DIN

RESET

DVDD

AD7708/

AD7718

SCLK

DOUT

SCLK

RFS

TFS

ADSP-2103 /

ADSP-2105

Figure 21. AD7708/AD7718-to-ADSP-2103/ADSP-2105

Interface

BASIC CONFIGURATION

The basic connection diagram for the AD7708/AD7718 in 10-

channel mode is shown in Figure 22. This shows both the AVDD

and DVDD pins of the converters being driven from the analog

5 V supply. Some applications will have AVDD and DVDD driven

from separate supplies. AVDD and DVDD can be operated inde-

pendently of each other, allowing the device to be operated with

5 V analog supply and 3 V digital supply or vice versa. The parts

can be operated in 8- or 10-channel configurations. In 8-channel

mode the user has two reference input options. This allows the

user to operate some channels in ratiometric mode and others

in absolute measurement mode. In 10-channel mode only one

reference option is available. An AD780/REF195, precision 2.5 V

reference, provides the reference source for the part. A quartz

crystal or ceramic resonator provides the 32.768 kHz master

clock source for the part. In some cases, it will be necessary to

connect capacitors on the crystal or resonator to ensure that it

does not oscillate at overtones of its fundamental operating fre-

quency. The values of capacitors will vary, depending on the

manufacturer’s specifications.

AD780 /

REF195

RECEIVE

(READ)

AIN6

AIN5

AIN4

AIN3

AIN2

AIN1

0.1 F

10 F

ANALOG 5V

SUPPLY

GND

VIN

VOUT

AGND

DGND

0.1 F

10 F

0.1 F

AVDD

DVDD

REF1IN(+)

REF1IN(–)

RESET

DOUT

DIN

SCLK

MCLKIN

MCLKOUT

CHIP

SELECT

SERIAL

DATA

(WRITE)

SERIAL

CLOCK

32kHz

CRYSTAL

ANALOG 5V

SUPPLY

AD7708/

AD7718

AIN8

AIN7

AIN9

AINCOM

AIN10

Figure 22. Basic Configuration for 10-Channel Mode

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