Preliminary Technical Data

AD7693

Rev. PrB | Page 21 of 24

CHAIN MODE, NO BUSY INDICATOR

This mode can be used to daisy-chain multiple AD7693s on

a 3-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 AD7693s is shown in

Figure 41, and the corresponding timing is given in Figure 42.

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

a rising edge on CNV initiates a conversion, selects the 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 AD7693 enters the acquisition phase and

powers down. The remaining data bits stored in the internal

shift register are clocked by subsequent SCK falling edges. For

each ADC, SDI feeds the input of the internal shift register and

is clocked by the SCK falling edge. Each ADC in the 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.

Although the rising edge can be used to capture the data, a

digital host using the SCK falling edge will allow a faster

reading rate and consequently more AD7693s in the chain,

provided the digital host has an acceptable hold time. The

maximum conversion rate can be reduced due to the total

readback time.

CLK

CONVERT

DATA IN

DIGITAL HOST

CNV

SCK

SDO

SDI

CNV

SCK

SDO

SDI

AD7693

B

AD7693

A

Figure 41. Chain Mode Without Busy Indicator Connection Diagram

SCK

1

2

3

30

31

32

CONVERSION

ACQUISITION

ACQUISITION

CNV

14

15

17

18

16

Figure 42. Chain Mode Without Busy Indicator Serial Interface Timing