AD7691 Analog Devices, AD7691 Datasheet - Page 20

• Manufacturer Part Number: AD7691
• Manufacturer: Analog Devices

Specifications of AD7691

• Resolution (bits): 18bit
• # Chan: 1
• Sample Rate: 250kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (2Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

AD7691
CS MODE, 4-WIRE WITHOUT BUSY INDICATOR
This mode is usually used when multiple AD7691s are
connected to an SPI-compatible digital host.
A connection diagram example using two AD7691s is shown in
Figure 39, and the corresponding timing is given in Figure 40.
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
SDI (CS1)
SDI (CS2)
ACQUISITION
SDO
CNV
SCK
t
SSDICNV
t
HSDICNV
CONVERSION
t
CONV
t
EN
SDI
AD7691
Figure 40. 4-Wire CS Mode Without Busy Indicator Serial Interface Timing
Figure 39. 4-Wire CS Mode Without Busy Indicator Connection Diagram
D17
CNV
SCK
1
t
HSDO
D16
SDO
2
D15
3
t
DSDO
t
SCKL
t
Rev. B | Page 20 of 28
SCKH
16
SDI
t
SCK
AD7691
17
D1
CNV
SCK
t
CYC
time elapses and then held high for the maximum possible
conversion time to avoid the generation of the busy signal
indicator. When the conversion is complete, the AD7691 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 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 18
falling edge, or when SDI goes high, whichever occurs first, SDO
returns to high impedance and another AD7691 can be read.
18
D0
ACQUISITION
SDO
t
ACQ
D17
19
DATA IN
CLK
CS2
CS1
CONVERT
DIGITAL HOST
D16
20
34
35
D1
36
D0
t
DIS
th
SCK