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AD7690

Data Sheet

Rev. C | Page 18 of 24

CS MODE, 3-WIRE WITH BUSY INDICATOR

This mode is usually used when a single AD7690 is connected

to an SPI-compatible digital host having an interrupt input.

The connection diagram is shown in Figure 36, and the

corresponding timing is given in Figure 37.

With SDI tied to VIO, a rising edge on CNV initiates a

conversion, selects the CS mode, and forces SDO to high

impedance. SDO is maintained in high impedance until the

completion of the conversion irrespective of the state of CNV.

Prior to the minimum conversion time, CNV can be used to

select other SPI devices, such as analog multiplexers, but CNV

must be returned low before the minimum conversion time

elapses and then held low for the maximum possible conversion

time to guarantee the generation of the busy signal indicator.

When the conversion is complete, SDO goes from high

impedance to low impedance. With a pull-up on the SDO line,

this transition can be used as an interrupt signal to initiate the

data reading controlled by the digital host. The AD7690 then

enters the acquisition phase and powers down. The data bits are

clocked out, MSB first, by subsequent SCK falling edges. 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 allows a faster reading rate, provided it has an acceptable

hold time. After the optional 19th SCK falling edge or when

CNV goes high (whichever occurs first), SDO returns to high

impedance.

If multiple AD7690s are selected at the same time, the SDO

output pin handles this contention without damage or induced

latch-up. Meanwhile, it is recommended to keep this contention

as short as possible to limit extra power dissipation.

Figure 36. 3-Wire CS Mode with Busy Indicator

Connection Diagram (SDI High)

Figure 37. 3-Wire CS Mode with Busy Indicator Serial Interface Timing (SDI High)

DATA IN

IRQ

CLK

CONVERT

VIO

DIGITAL HOST

47kΩ

CNV

SCK

SDO

SDI

VIO

AD7690

SDO

D17

D16

tDIS

SCK

tSCK

tSCKL

tSCKH

tHSDO

tDSDO

CNV

CONVERSION

ACQUISITION

tCONV

tCYC

ACQUISITION

SDI = 1

tCNVH

tACQ

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