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AD4000/AD4004/AD4008

Data Sheet

Rev. C | Page 34 of 36

DAISY-CHAIN MODE

Use this mode to daisy-chain multiple AD4000/AD4004/AD4008

devices on a 3-wire or 4-wire serial interface. This feature is

useful for reducing component count and wiring connections,

for example, in isolated multiconverter applications or for

systems with a limited interfacing capacity. Data readback is

analogous to clocking a shift register.

A connection diagram example using two AD4000/AD4004/

AD4008 devices is shown in Figure 62, and the corresponding

timing diagram is shown in Figure 63.

When SDI and CNV are low, SDO is driven low. With SCK low,

a rising edge on CNV initiates a conversion, selects daisy-chain

mode, and disables the busy indicator. In this mode, CNV is

held high during the conversion phase and the subsequent data

readback.

When the conversion is complete, the MSB is output onto SDO,

and the AD4000/AD4004/AD4008 enter the acquisition phase

and power down. The remaining data bits stored in the internal

shift register are clocked out of SDO by subsequent SCK falling

edges. For each ADC, SDI feeds the input of the internal shift

the daisy-chain outputs its data MSB first, and 16 × N clocks are

required to read back the N ADCs. The data is valid on both

SCK edges. The maximum conversion rate is reduced because of

the total readback time.

It is possible to write to each ADC register in daisy-chain mode.

The timing diagram is shown in Figure 48. This mode requires

4-wire operation because data is clocked in on the SDI line with

CNV held low. The same command byte and register data can

be shifted through the entire chain to program all ADCs in the

chain with the same register contents, which requires 8 × (N + 1)

clocks for N ADCs. It is possible to write different register contents

to each ADC in the chain by writing to the furthest ADC in the

chain first, using 8 × (N + 1) clocks, and then the second furthest

ADC with 8 × N clocks, and so forth until reaching the nearest

ADC in the chain, which requires 16 clocks for the command

and register data. It is not possible to read register contents in

daisy-chain mode; however, the six status bits can be enabled if

the user wants to determine the ADC configuration. Note that

enabling the status bits requires six extra clocks to clock out the

ADC result and the status bits per ADC in the chain. Turbo

mode cannot be used in daisy-chain mode.

CONVERT

DATA IN

CLK

DIGITAL HOST

DEVICE B

DEVICE A

AD4000/

AD4004/

AD4008

SDI

SDO

CNV

SCK

AD4000/

AD4004/

AD4008

SDI

SDO

CNV

SCK

Figure 62. Daisy-Chain Mode, Connection Diagram

SDOA = SDIB

DA15

DB15

DB14

DB13

DA14

DA13

DA1

DA0

DA1

DA0

DB1

DB0

SCK

tSSDISCK

tHSDISCK

CONVERSION

ACQUISITION

tCONV

tCYC

tACQ

ACQUISITION

CNV

tSCK

tSCKL

tSCKH

SDIA = 0

SDOB

DA15

DA14

tHSDO

tDSDO

tQUIET2

tHSCKCNV

tDIS

tQUIET2

tEN

Figure 63. Daisy-Chain Mode, Serial Interface Timing Diagram

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