AD7980 Analog Devices, AD7980 Datasheet - Page 19

• Manufacturer Part Number: AD7980
• Manufacturer: Analog Devices

Specifications of AD7980

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

CS MODE 4-WIRE, WITHOUT BUSY INDICATOR
This mode is usually used when multiple AD7980s are
connected to an SPI-compatible digital host.
A connection diagram example using two AD7980s is shown in
Figure 35, and the corresponding timing is given in Figure 36.
With SDI high, a rising edge on CNV initiates a conversion,
selects the CS mode, and forces SDO to high impedance. In this
mode, CNV must be held high during the conversion phase and
the subsequent data readback (if SDI and CNV are low, SDO is
driven low). Prior to the minimum conversion time, SDI can be
used to select other SPI devices, such as analog multiplexers,
but SDI must be returned high before the minimum conversion
time elapses and then held high for the maximum conversion
time to avoid the generation of the busy signal indicator.
SCK
SDO
CNV
AQUISITION
SDI(CS1)
t
SSDICNV
SDI(CS2)
t
HSDICNV
CONVERSION
t
CONV
t
EN
SDI
AD7980
Figure 36. 4-Wire CS Mode Without Busy Indicator Serial Interface Timing
Figure 35. 4-Wire CS Mode Without Busy Indicator Connection Diagram
CNV
SCK
D15
1
t
HSDO
SDO
D14
2
D13
3
t
DSDO
t
SCKL
t
14
Rev. B | Page 19 of 28
SCKH
SDI
t
SCK
15
D1
AD7980
CNV
SCK
t
CYC
When the conversion is complete, the AD7980 enters the
acquisition phase and powers down. Each ADC result can be
read by bringing its SDI input low, which consequently outputs
the MSB onto SDO. The remaining data bits are then clocked by
subsequent SCK falling edges. The data is valid on both SCK
edges. Although the rising edge can be used to capture the data,
a digital host using the SCK falling edge allows a faster reading
rate provided it has an acceptable hold time. After the 16th SCK
falling edge or when SDI goes high, whichever is earlier, SDO
returns to high impedance and another AD7980 can be read.
16
D0
AQUISITION
t
SDO
ACQ
D15
17
CS2
CS1
CONVERT
DATA IN
CLK
DIGITAL HOST
D14
18
30
31
D1
32
D0
t
DIS
AD7980