AD7923

–13–

REV. 0

two address bits indicating which channel the conversion result

corresponds to, followed by the 12 bits of conversion data. For

applications where power consumption is of concern, the power-

down modes should be used between conversions or bursts of

several conversions to improve power performance. See the

Modes of Operation section.

SERIAL

INTERFACE

AD780

2.5V

AD7923

0.1 F

C/ P

0.1 F

10 F

3V

SUPPLY

5V

SUPPLY

0.1 F

10 F

AGND

•

•

SCLK

DOUT

CS

DIN

NOTE: ALL UNUSED INPUT CHANNELS MUST BE CONNECTED TO AGND

Figure 10. Typical Connection Diagram

Analog Input Selection

Any one of four analog input channels may be selected for con-

version by programming the multiplexer with the address bits

ADD1 and ADD0 in the Control Register. The channel configu-

rations are shown in Table II.

The AD7923 may also be configured to automatically cycle

through a number of channels as selected. The sequencer fea-

ture is accessed via the SEQ1 and SEQ0 bits in the Control

Register. (See Table IV). The AD7923 can be programmed to

continuously convert on a number of consecutive channels in

ascending order from Channel 0 to a selected final channel as

determined by the channel address bits ADD1 and ADD0. This

is possible if the SEQ1 and SEQ0 bits are set to 1,1. The next

serial transfer will then act on the sequence programmed by

executing a conversion on Channel 0. The next serial transfer

will result in a conversion on Channel 1, and so on, until the

channel selected via the address bits ADD1, ADD0 is reached.

It is not necessary to write to the Control Register again once a

sequencer operation has been initiated. The WRITE bit must be

set to zero or the DIN line tied low to ensure that the Control

Register is not accidently overwritten, or the sequence operation

interrupted. If the Control Register is written to at any time

during the sequence, the user must ensure that the SEQ1 and

SEQ0 bits are set to 1,0 to avoid interrupting the automatic

conversion sequence. This pattern will continue until the AD7923

is written to and the SEQ1 and SEQ0 bits are configured with

any bit combination except 1,0 resulting in the termination of

the sequence. If uninterrupted, however (WRITE bit = 0, or

WRITE bit = 1 and SEQ1 and SEQ0 bits are set to 1,0), then

upon completion of the sequence, the AD7923 sequencer will

return to the Channel 0 and commence the sequence again.

Regardless of which channel selection method is used, the 16-bit

word output from the AD7923 during each conversion will

always contain two leading zeros, two channel address bits that

the conversion result corresponds to, followed by the 12-bit

conversion result. (See the Serial Interface section.)

Digital Inputs

The digital inputs applied to the AD7923 are not limited by

the maximum ratings that limit the analog inputs. Instead, the

digital inputs applied can go to 7 V and are not restricted by the

Another advantage of SCLK, DIN, and

CS not being restricted by

issues are avoided. If

CS, DIN, or SCLK is applied before AV

there is no risk of latch-up as there would be on the analog inputs

ADC to easily interface to both 3 V and 5 V processors. For

able to interface to 3 V processors. Care should be taken to

(See the Absolute Maximum Ratings section.)

R3

R2

R4

AD7923

DSP/ P

0.1 F

V

DOUT

TWOS

COMPLEMENT

011…111

000…000

100…000

(= 0V)

(= 2

0V

V

R1

R1

R2

R3

R4

•

•

Figure 9. Handling Bipolar Signals