AD5674/AD5674R/AD5679/AD5679R

Data Sheet

Rev. B | Page 26 of 32

enabled for the duration of the read operation, after which the

SDO output is disabled again. Command 1001 is reserved for the

readback function. This command, in association with the

address bits (A3 to A0), selects the DAC input register to read

(see Table 10 and Table 11). During readback, only one input

register can be selected. The remaining data bits in the write

sequence are don’t care bits. During the next SPI write, the data

appearing on the SDO output contains the data from the

previously addressed register.

For example, to read back the DAC register for Channel 0,

implement the following sequence:

1. Write 0x900000 to the AD5674/AD5674R/AD5679/

AD5679R input register. This configures the device for

read mode with the DAC register of Channel 0 selected.

Note that all data bits, DB15 to DB0, are don’t care bits.

2. Follow Step 1 with a second write, a no operation (NOP)

condition, 0x000000 or 0xF00000 when in daisy-chain

mode. During this write, the data from the register is

clocked out on the SDO line. DB23 to DB20 contain

undefined data, and the last 20 bits contain the DB19 to

DB0 DAC register contents.

When SYNC is high, the SDO pin is driven by a weak latch that

holds the last data bit. The SDO pin can be overdriven by the

SDO pin of another device. Multiple devices can be read using

the same SPI interface.

POWER-DOWN OPERATION

Command 0100 is designated for the power-down function (see

Table 10). These power-down modes are software programmable

by setting 16 bits, Bit DB15 to Bit DB0, in the input shift register.

There are two bits associated with each DAC channel. Table 13

shows how the state of the two bits corresponds to the mode of

operation of the device.

Any or all DACs (DAC 0 to DAC 15) power down to the

selected mode by setting the corresponding bits. See Table 14

and Table 15 for the contents of the input shift register during

the power-down/power-up operation.

Table 13. Modes of Operation

Operating Mode

PD1

PD0

Normal Operation

0

0

Power-Down Modes

1 kΩ to GND

0

1

When both Bit PD1 and Bit PD0 in the input shift register are set

to 0, the device works normally with a typical power consumption

of 2.3 mA at 5 V. However, for the 1 kΩ power-down mode, the

supply current typically falls to 2 µA. In addition to this fall, the

output stage switches internally from the amplifier output to a

resistor network of a known value. Therefore, the DAC channel

output impedance is defined when the channel is powered down

by internally connecting the output to GND through a 1 kΩ

resistor. Figure 62 shows the output stage.

Figure 62. Output Stage During Power-Down

The bias generator, output amplifier, resistor string, and other

associated linear circuitry shut down when power-down mode is

activated. However, the contents of the DAC register are unaffected

when in power-down. The DAC register updates while the device

is in power-down mode. The time required to exit power-down is

typically 3 µs for VDD = 5 V.

To reduce the current consumption further, power off the on-chip

reference. See the Internal Reference Setup section.

Table 14. 24-Bit Input Shift Register Contents of Power-Down/Power-Up Operation for Output Channels DAC 7 to DAC 0

[DB23:DB20]

DB19

[DB18:DB16]

DAC 7

DAC 6

DAC 5

DAC 4

DAC 3

DAC 2

DAC 1

DAC 0

[DB15:DB14]

[DB13:DB12]

[DB11:DB10]

[DB9:DB8]

[DB7:DB6]

[DB5:DB4]

[DB3:DB2]

[DB1:DB0]

0100

0

XXX1

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

Table 15. 24-Bit Input Shift Register Contents of Power-Down/Power-Up Operation for Output Channels DAC 15 to DAC 8

[DB23:DB20]

DB19

[DB18:DB16]

DAC 15

DAC 14

DAC 13

DAC 12

DAC 11

DAC 10

DAC 9

DAC 8

[DB15:DB14]

[DB13:DB12]

[DB11:DB10]

[DB9:DB8]

[DB7:DB6]

[DB5:DB4]

[DB3:DB2]

[DB1:DB0]

0100

1

XXX1

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

[PD1:PD0]

1

X means don’t care.

RESISTOR

NETWORK

VOUT

DAC

POWER-DOWN

CIRCUITRY

AMPLIFIER

1

X means don’t care.