AD4004 datasheet(29/36 Pages) AD

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Data Sheet

AD4000/AD4004/AD4008

Rev. C | Page 29 of 36

CS MODE, 3-WIRE WITHOUT BUSY INDICATOR

This mode is typically used when a single AD4000/AD4004/

AD4008 device is connected to an SPI-compatible digital host.

The connection diagram is shown in Figure 52, and the

corresponding timing diagram is shown in Figure 53.

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

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

impedance. After a conversion is initiated, it continues until

completion irrespective of the state of CNV. This feature can be

useful, for instance, to bring CNV low to select other SPI

devices, such as analog multiplexers; however, CNV must be

returned high before the minimum conversion 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 AD4000/AD4004/AD4008

enter the acquisition phase and power down. When CNV goes

low, the MSB is output 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 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.

There must not be any digital activity on SCK during the

conversion.

AD4000/

AD4004/

AD4008

SDI

SDO

CNV

SCK

CONVERT

DATA IN

CLK

DIGITAL HOST

VIO

Figure 52. CS Mode, 3-Wire Without Busy Indicator Connection Diagram (SDI High)

SDO

D15

D14

D13

tDIS

SCK

tSCK

tSCKL

tSCKH

tHSDO

tDSDO

CNV

CONVERSION

ACQUISITION

tCYC

ACQUISITION

SDI = 1

tCNVH

tACQ

tEN

tQUIET2

tCONV

Figure 53. CS Mode, 3-Wire Without Busy Indicator Serial Interface Timing Diagram (SDI High)

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