AD7708 Analog Devices, AD7708 Datasheet - Page 36

• Manufacturer Part Number: AD7708
• Description: 16-Bit 8/10-Channel, Low Voltage, Low Power, Sigma Delta ADC
• Manufacturer: Analog Devices

Specifications of AD7708

• Resolution (bits): 16bit
• # Chan: 10
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref/PGA Gain) p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: SOIC,SOP

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.
AD7708/AD7718
ADSP-2103 /
ADSP-2105
SCLK
RFS
TFS
DR
DT
DV
DD
CS
DOUT
DIN
SCLK
RESET
AD7708/
AD7718
BASIC CONFIGURATION
The basic connection diagram for the AD7708/AD7718 in 10-
channel mode is shown in Figure 22. This shows both the AV
and DV
5 V supply. Some applications will have AV
from separate supplies. AV
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.
ANALOG 5V
ANALOG 5V
SUPPLY
SUPPLY
V
AD780 /
REF195
IN
GND
DD
V
OUT
10 F
pins of the converters being driven from the analog
10 F
0.1 F
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
AIN8
REF1IN(+)
REF1IN(–)
AIN9
AIN10
AINCOM
DD
0.1 F
and DV
AGND
AV
AD7708/
AD7718
DD
DD
DV
DGND
DD
can be operated inde-
MCLKOUT
DD
MCLKIN
RESET
SCLK
DOUT
0.1 F
and DV
DIN
CS
P1
P2
DD
5V
32kHz
CRYSTAL
CHIP
SELECT
RECEIVE
(READ)
SERIAL
DATA
(WRITE)
SERIAL
CLOCK
driven
DD