AD4000 datasheet(32/36 Pages) AD

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AD4000/AD4004/AD4008

Data Sheet

Rev. C | Page 32 of 36

CS MODE, 4-WIRE WITHOUT BUSY INDICATOR

This mode is typically used when multiple AD4000/AD4004/

AD4008 devices are connected to an SPI-compatible digital host.

A connection diagram example using two AD4000/AD4004/

AD4008 devices is shown in Figure 58, and the corresponding

timing diagram is shown in Figure 59.

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

select other SPI devices, such as analog multiplexers; however,

SDI 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. 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 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 SDI goes high (whichever occurs

first), SDO returns to high impedance and another AD4000/

AD4004/AD4008 can be read.

AD4000/

AD4004/

AD4008

SDI

SDO

CNV

SCK

DEVICE A

CONVERT

DATA IN

CLK

DIGITAL HOST

AD4000/

AD4004/

AD4008

SDI

SDO

CNV

SCK

DEVICE B

CS1

CS2

Figure 58. CS Mode, 4-Wire Without Busy Indicator Connection Diagram

SDO

D15

D14

D13

tDIS

SCK

tHSDO

tDSDO

tEN

CONVERSION

ACQUISITION

tCONV

tCYC

tACQ

ACQUISITION

SDI(CS1)

CNV

tSSDICNV

tHSDICNV

tSCK

tSCKL

tSCKH

D15

D14

SDI(CS2)

tQUIET2

Figure 59. CS Mode, 4-Wire Without Busy Indicator Serial Interface Timing Diagram

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