AD7940 datasheet(16/24 Pages) AD

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AD7693

Preliminary Technical Data

Rev. PrB | Page 16 of 24

SUPPLYING THE ADC FROM THE REFERENCE

ADSP-219x. In this mode, the AD7693 can use either a 3-wire

or 4-wire interface. A 3-wire interface using the CNV, SCK, and

SDO signals minimizes wiring connections useful, for instance,

in isolated applications. A 4-wire interface using the SDI, CNV,

SCK, and SDO signals allows CNV, which initiates the

conversions, to be independent of the readback timing (SDI).

This is useful in low jitter sampling or simultaneous sampling

applications.

For simplified applications, the AD7693, with its low operating

current, can be supplied directly using the reference circuit

shown in Figure 32. The reference line can be driven by

•

The system power supply directly.

•

A reference voltage with enough current output capability,

such as the ADR43x.

When in chain mode, the AD7693 provides a daisy-chain

feature using the SDI input for cascading multiple ADCs on a

single data line similar to a shift register.

•

A reference buffer, such as the AD8031, which can also

filter the system power supply, as shown in Figure 32.

AD8031

AD7693

VIO

REF

VDD

10µF

1µF

10k

1µF

1OPTIONAL REFERENCE BUFFER AND FILTER.

The mode in which the part operates depends on the SDI level

when the CNV rising edge occurs. The CS mode is selected if

SDI is high, and the chain mode is selected if SDI is low. The

SDI hold time is such that when SDI and CNV are connected

together, the chain mode is selected.

In either mode, the AD7693 offers the option of forcing a start

bit in front of the data bits. This start bit can be used as a busy

signal indicator to interrupt the digital host and trigger the data

reading. Otherwise, without a busy indicator, the user must

timeout the maximum conversion time prior to readback.

Figure 32. Example of Application Circuit

DIGITAL INTERFACE

The busy indicator feature is enabled

Though the AD7693 has a reduced number of pins, it offers

flexibility in its serial interface modes.

•

In the CS mode if CNV or SDI is low when the ADC

conversion ends (see Figure 36 and Figure 40).

When in

mode, the AD7693 is compatible with SPI, QSPI,

digital hosts, and DSPs, for example, Blackfin® ADSP-BF53x or

•

In the chain mode if SCK is high during the CNV rising

edge (see Figure 44).

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