EVAL-SDP-CB1Z View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
'EVAL-SDP-CB1Z' PDF : 28 Pages View PDF
Data Sheet
AD7691
CS MODE, 3-WIRE WITH BUSY INDICATOR
This mode is usually used when a single AD7691 is connected
to an SPI-compatible digital host having an interrupt input.
The connection diagram is shown in Figure 37, and the
corresponding timing is given in Figure 38.
With SDI tied to VIO, a rising edge on CNV initiates a
conversion, selects the CS mode, and forces SDO to high
impedance. SDO is maintained in high impedance until the
completion of the conversion irrespective of the state of CNV.
Prior to the minimum conversion time, CNV can select other
SPI devices, such as analog multiplexers, but CNV must be
returned low before the minimum conversion time elapses and
then held low for the maximum possible conversion time to
guarantee the generation of the busy signal indicator. When the
conversion is complete, SDO goes from high impedance to low
impedance. With a pull-up on the SDO line, this transition is
used as an interrupt signal to initiate the data reading controlled
by the digital host. When using this option, select the value of
the pull-up resistor such that it maintains an appropriate rise
time on the SDO line for the application. This is a function of
the resistance of the pull-up and the capacitance of the SDO
line. The AD7691 then enters the acquisition phase and powers
down. The data bits are 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 can allow a faster reading
rate, provided it has an acceptable hold time. After the optional
19th SCK falling edge, or when CNV goes high, whichever
occurs first, SDO returns to high impedance.
If multiple AD7691 devices are selected at the same time, the
SDO output pin handles this contention without damage or
induced latch-up. Meanwhile, it is recommended to keep this
contention as short as possible to limit extra power dissipation.
CNV
VIO
SDI AD7691 SDO
SCK
CONVERT
VIO
DIGITAL HOST
47kΩ
DATA IN
IRQ
CLK
Figure 37. 3-Wire CS Mode with Busy Indicator
Connection Diagram (SDI High)
SDI = 1
tCNVH
CNV
ACQUISITION
tCONV
CONVERSION
SCK
SDO
tCYC
tACQ
ACQUISITION
tSCKL
tSCK
1
2
3
17
18
19
tHSDO
tSCKH
tDSDO
tDIS
D17
D16
D1
D0
Figure 38. 3-Wire CS Mode with Busy Indicator Serial Interface Timing (SDI High)
Rev. E | Page 19 of 28
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