AD76851 데이터 시트보기 (PDF) - Analog Devices

부품명

상세내역

제조사

AD76851

18-Bit, 2 MSPS PulSAR 15 mW ADC in LFCSP (QFN)

Analog Devices 

AD7986

CHAIN MODE WITH BUSY INDICATOR

This mode can also be used to daisy-chain multiple AD7986

devices on a 3-wire serial interface while providing a busy

indicator. 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 three AD7986 devices is

shown in Figure 35, and the corresponding timing is given in

Figure 36.

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

high, a rising edge on CNV initiates a conversion, selects the

chain mode, and enables the busy indicator feature. In this

mode, CNV is held high during the conversion phase and the

subsequent data readback. When all ADCs in the chain have

completed their conversions, the SDO pin of the ADC closest to

the digital host (see the AD7986 ADC labeled C in Figure 35) is

driven high. This transition on SDO can be used as a busy indicator

to trigger the data readback controlled by the digital host. The

AD7986 then enters the acquisition phase and powers down.

The data bits stored in the internal shift register are clocked out,

MSB first, 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 18 × N + 1 clocks are required to read back the N ADCs.

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

host using the SCK falling edge allows a faster reading rate and

consequently more AD7986 devices in the chain, provided that

the digital host has an acceptable hold time.

CNV

SDI AD7986 SDO

A

SCK TURBO

CNV

SDI AD7986 SDO

B

SCK TURBO

CNV

SDI AD7986 SDO

C

SCK TURBO

Figure 35. Chain Mode with Busy Indicator Connection Diagram

CONVERT

DIGITAL HOST

DATA IN

IRQ

CLK

TURBO = 0

CNV = SDIA

tCONV

ACQUISITION

CONVERSION

SCK

tHSCKCNV

SDOA = SDIB

tQUIET

tEN

SDOB = SDIC

SDOC

tDSDOSDI

tDSDOSDI

tCYC

tACQ

ACQUISITION

tSCKH

tSCK

1234

17 18 19 20 21

tSSDISCK

tHSDISCK

tSCKL

35 36 37 38 39

DA17 DA16 DA15

tHSDO

tDSDO

DA1 DA0

DB17 DB16 DB15

DB1 DB0 DA17 DA16

DA1 DA0

DC17 DC16 DC15

DC1 DC0 DB17 DB16

DB1 DB0 DA17 DA16

Figure 36. Chain Mode with Busy Indicator Serial Interface Timing

53 54 55

tDSDOSDI

tDSDOSDI

tDSDOSDI

DA1 DA0

Rev. B | Page 24 of 28

Share Link: