AD7687BCPZ-R2 datasheet(24/27 Pages) AD

24 / 27 page

Data Sheet

AD7687

Rev. E | Page 23 of 26

CHAIN MODE WITHOUT BUSY INDICATOR

Use this mode to daisy-chain multiple AD7687 devices on a

3-wire serial interface. This feature is useful for reducing

component count and wiring connections, for isolated

multiconverter applications, or for systems with a limited

interfacing capacity (for example). Data readback is analogous

to clocking a shift register.

Figure 42 shows a connection diagram example using two

AD7687 devices and Figure 43 gives the corresponding timing.

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

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 AD7687 enters the acquisition phase

and powers down. The remaining data bits stored in the

internal shift register are then shifted out by subsequent SCK

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

shift register; these data bits are also shifted in by the SCK

falling edge. Each of the N ADCs in the chain outputs its data

MSB first. 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 and, consequently, more

AD7687 devices in the chain (provided the digital host has an

acceptable hold time). After the 16 × Nth SCK falling edge or

CNV rising edge, whichever is earlier, SDO is driven low again.

The maximum conversion rate can be reduced due to the total

readback time. For example, using a digital host with a 3 ns set-

up time and 3 V interface, up to eight AD7687 devices daisy-

chained on a 3-wire port can be run at a maximum effective

conversion rate of 220 kSPS.

CLK

CONVERT

DATA IN

DIGITAL HOST

CNV

SCK

SDO

SDI

AD7687

CNV

SCK

SDO

SDI

AD7687

Figure 42. Chain Mode Without BUSY Indicator Connection Diagram

SDOA = SDIB

DA15

DA14

DA13

SCK

tSSDISCK

tHSDISC

tEN

CONVERSION

ACQUISITION

tCONV

tCYC

tACQ

ACQUISITION

CNV

DA1

tSCK

tSCKL

tSCKH

DA0

SDIA = 0

SDOB

DB15

DB14

DB13

DA1

DB1

DB0

DA15

DA14

tHSDO

tDSDO

tSSCKCNV

tHSCKCNV

DA0

Figure 43. Chain Mode Without BUSY Indicator Serial Interface Timing

AD7687BCPZ-R2 数据表(PDF) 24 Page - Analog Devices

AD7687BCPZ-R2 数据表(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

数据表下载

链接网址

AD7687BCPZ-R2 数据表(PDF) 24 Page - Analog Devices

AD7687BCPZ-R2 数据表(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

数据表 下载

链接网址

数据表下载