AD5378ABC datasheet(23/28 Pages) AD

23 / 28 page

Preliminary Technical Data

AD5378

Rev. PrA | Page 23 of 28

Daisy-Chain Mode

For systems that contain several DACs, the SDO pin can be

used to daisy-chain several devices together. This daisy-chain

mode can be useful in system diagnostics and in reducing the

number of serial interface lines.

Connecting the DCEN (daisy-chain enable) pin high enables

daisy-chain mode. The first falling edge of SYNC starts the

write cycle. The SCLK is continuously applied to the input shift

applied, the data ripples out of the shift register and appears on

the SDO line. This data is clocked out on the rising edge of

SCLK and is valid on the falling edge. By connecting this line to

the DIN input on the next device in the chain, a multidevice

interface is constructed. For each AD5378 in the system,

24 clock pulses are required. Therefore, the total number of

clock cycles must equal 24N, where N is the total number of

AD5378 devices in the chain. If fewer than 24 clocks are

applied, the write sequence is ignored.

When the serial transfer to all devices is complete, SYNC

should be taken high. This latches the input data in each device

in the daisy chain and prevents any additional data from being

clocked into the input shift register.

A continuous SCLK source can be used if SYNC is held low for

the correct number of clock cycles. Alternatively, a burst clock

containing the exact number of clock cycles can be used and

SYNC taken high after the final clock to latch the data.

When the transfer to all input registers is complete, a common

LDAC signal updates all DAC registers, and all analog outputs

are updated simultaneously.

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