AD7946 Analog Devices, AD7946 Datasheet - Page 19

• Manufacturer Part Number: AD7946
• Manufacturer: Analog Devices

Specifications of AD7946

• Resolution (bits): 14bit
• # Chan: 1
• Sample Rate: 500kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p
• Adc Architecture: SAR
• Pkg Type: CSP,SOP

CS MODE 4-WIRE, NO BUSY INDICATOR
This mode is usually used when multiple AD7946s are
connected to an SPI-compatible digital host.
A connection diagram example using two AD7946s is shown in
Figure 37, and the corresponding timing is given in Figure 38.
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 high before the minimum conversion
SDI(CS1)
SDI(CS2)
ACQUISITION
SDO
CNV
SCK
t
SSDICNV
t
HSDICNV
CONVERSION
t
CONV
t
EN
SDI
AD7946
D13
Figure 38. CS Mode 4-Wire, No BUSY Indicator Serial Interface Timing
CNV
SCK
Figure 37. CS Mode 4-Wire, No BUSY Indicator Connection Diagram
1
t
HSDO
D12
SDO
2
D11
3
t
DSDO
t
SCKL
t
SCKH
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12
SDI
t
SCK
AD7946
13
D1
CNV
SCK
t
CYC
time and held high until the maximum conversion time to
avoid the generation of the BUSY signal indicator. When the
conversion is complete, the AD7946 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 subse-
quent 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 14
falling edge, or when SDI goes high, whichever is earlier, SDO
returns to high impedance and another AD7946 can be read.
14
D0
ACQUISITION
SDO
t
ACQ
D13
15
DATA IN
CLK
CS2
CS1
CONVERT
DIGITAL HOST
D12
16
26
27
D1
28
D0
t
DIS
AD7946
th
SCK