AD5644R datasheet(21/28 Pages) AD

21 / 28 page

AD5624R/AD5644R/AD5664R

Rev. A | Page 21 of 28

At this stage, the SYNC line can be kept low or be brought high. In

either case, it must be brought high for a minimum of 15 ns before

the next write sequence so that a falling edge of SYNC can initiate

the next write sequence.

Since the SYNC buffer draws more current when VIN = 2 V than

it does when VIN = 0.8 V, SYNC should be idled low between

write sequences for even lower power operation. As mentioned

previously, it must, however, be brought high again just before

the next write sequence.

INPUT SHIFT REGISTER

The input shift register is 24 bits wide (see Figure 52). The first

two bits are don’t care bits. The next three are the command

bits, C2 to C0 (see Table 8), followed by the 3-bit DAC address,

A2 to A0 (see Table 9), and then the 16-, 14-, 12-bit data-word.

The data-word comprises the 16-, 14-, 12-bit input code

followed by 0, 2, or 4 don’t care bits, for the AD5664R,

AD5644R, and AD5624R, respectively (see Figure 52, Figure 53,

and Figure 54). These data bits are transferred to the DAC

Table 8. Command Definition

Command

Write to input register n

Update DAC register n

Write to input register n, update all

(software LDAC)

Write to and update DAC channel n

Power down DAC (power-up)

Reset

LDAC register setup

Internal reference setup (on/off )

Table 9. Address Command

Address (n)

DAC A

DAC B

DAC C

DAC D

All DACs

SYNC INTERRUPT

In a normal write sequence, the SYNC line is kept low for at least

24 falling edges of SCLK, and the DAC is updated on the 24th

falling edge. However, if SYNC is brought high before the 24th

falling edge, then this acts as an interrupt to the write sequence.

The input shift register is reset and the write sequence is seen as

invalid. Neither an update of the DAC register contents nor a

change in the operating mode occurs (see Figure 55).

D15 D14 D13 D12 D11 D10

DB23 (MSB)

DB0 (LSB)

COMMAND BITS

ADDRESS BITS

DATA BITS

Figure 52. AD5664R Input Shift Register Contents

D11 D10

D13 D12

DB23 (MSB)

DB0 (LSB)

COMMAND BITS

ADDRESS BITS

DATA BITS

Figure 53. AD5644R Input Shift Register Contents

XXX

D11 D10

DB23 (MSB)

DB0 (LSB)

COMMAND BITS

ADDRESS BITS

DATA BITS

Figure 54. AD5624R Input Shift Register Contents

DIN

DB23

DB0

VALID WRITE SEQUENCE, OUTPUT UPDATES

ON THE 24TH FALLING EDGE

SYNC

SCLK

INVALID WRITE SEQUENCE:

SYNC HIGH BEFORE 24TH FALLING EDGE

Figure 55. SYNC Interrupt Facility

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