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AD7980 Datasheet(PDF) 17 Page - Analog Devices

Part No. AD7980
Description  16-bit, 1 MSPS PulSAR ADC in MSOP/QFN
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD7980 Datasheet(HTML) 17 Page - Analog Devices

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Preliminary Technical Data
AD7980
Rev Pr C | Page 17 of 22
CS MODE 4-WIRE WITH BUSY INDICATOR
This mode is usually used when a single AD7980 is connected
to an SPI compatible digital host, which has an interrupt input,
and it is desired to keep CNV, which is used to sample the
analog input, independent of the signal used to select the data
reading. This requirement is particularly important in
applications where low jitter on CNV is desired.
The connection diagram is shown in Figure 21 and the
corresponding timing is given in Figure 22.
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 could
be used to select other SPI devices, such as analog multiplexers,
but SDI must be returned low before the minimum conversion
time and held low until the maximum conversion time to
guarantee the generation of the BUSY signal indicator. When
the conversion is complete, SDO goes from high impedance to
low. With a pull-up on the SDO line, this transition can be used
as an interrupt signal to initiate the data readback controlled by
the digital host. The AD7980 then enters the acquisition phase
and powers down. The data bits are then clocked out, MSB first,
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 will allow a faster
reading rate provided it has an acceptable hold time. After the
optional 17th SCK falling edge, or SDI going high, whichever is
earlier, the SDO returns to high impedance.
CNV
SCK
SDO
SDI
DATA IN
IRQ
CLK
CONVERT
CS1
VIO
DIGITAL HOST
47k
Ω
AD7980
Figure 21. CS Mode 4-Wire with BUSY Indicator Connection Diagram
SDO
D15
D14
D1
D0
tDIS
SCK
1
2
3
15
16
17
tSCK
tSCKL
tSCKH
tHSDO
tDSDO
tEN
CONVERSION
ACQUISITION
tCONV
tCYC
tACQ
ACQUISITION
SDI
CNV
tSSDICNV
tHSDICNV
Figure 22. CS Mode 4-Wire with BUSY Indicator Serial Interface Timing


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