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AD7686

Rev. B | Page 17 of 28

CS MODE 3-WIRE, NO BUSY INDICATOR

This mode is most often used when a single AD7686 is

connected to an SPI-compatible digital host. The connection

diagram is shown in Figure 33, and the corresponding timing is

provided in Figure 34.

With SDI tied to VIO, a rising edge on CNV initiates a

conversion, selects the CS mode, and forces SDO to high

impedance. Once a conversion is initiated, it continues to

completion irrespective of the state of CNV. For instance, it

could be useful to bring CNV low to select other SPI devices,

such as analog multiplexers. However, CNV must be returned

high before the minimum conversion time and held high until

the maximum conversion time to avoid generating the busy

signal indicator. When the conversion is complete, the AD7686

enters the acquisition phase and powers down. When CNV

goes low, the MSB is output 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

CNV goes high, whichever occurs first, SDO returns to high

impedance.

CNV

SCK

SDO

SDI

DATA IN

CLK

CONVERT

VIO

DIGITAL HOST

AD7686

Figure 33. CS Mode 3-Wire, No Busy Indicator

Connection Diagram (SDI High)

SDO

D15

D14

D13

tDIS

SCK

tSCK

tSCKL

tSCKH

tHSDO

tDSDO

CNV

CONVERSION

ACQUISITION

tCONV

tCYC

ACQUISITION

SDI = 1

tCNVH

tACQ

tEN

Figure 34. CS Mode 3-Wire, No Busy Indicator Serial Interface Timing (SDI High)

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