AD5624R/AD5644R/AD5664R

Rev. A | Page 22 of 28

POWER-ON RESET

The AD5624R/AD5644R/AD5664R family contains a power-on

reset circuit that controls the output voltage during power-up.

The AD5624R/AD5644R/AD5664R DACs output power up to

0 V and the output remains there until a valid write sequence is

made to the DACs. This is useful in applications where it is

important to know the state of the output of the DACs while

they are in the process of powering up.

SOFTWARE RESET

The AD5624R/AD5644R/AD5664R contain a software reset

function. Command 101 is reserved for the software reset

function (see Table 8). The software reset command contains

two reset modes that are software programmable by setting bit

DB0 in the control register.

Table 10 shows how the state of the bit corresponds to the

software reset modes of operation of the devices. Table 12 shows

the contents of the input shift register during the software reset

mode of operation.

Table 10. Software Reset Modes for the

AD5624R/AD5644R/AD5664R

DB0

Registers Reset to Zero

0

DAC register

Input shift register

1 (Power-On Reset)

DAC register

Input shift register

LDAC register

Power-down register

Internal reference setup register

POWER-DOWN MODES

The AD5624R/AD5644R/AD5664R contain four separate modes

of operation. Command 100 is reserved for the power-down

function (see Table 8). These modes are software programmable

by setting two bits (DB5 and DB4) in the control register. Table

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

operation of the device. All DACs, (DAC D to DAC A) can be

powered down to the selected mode by setting the corresponding

four bits (DB3, DB2, DB1, and DB0) to 1.

By executing the same Command 100, any combination of DACs

can be powered up by setting the bits (DB5 and DB4) to normal

operation mode. To select which combination of DAC channels

to power-up, set the corresponding four bits (DB3, DB2, DB1,

and DB0) to 1. See Table 13 for contents of the input shift register

during power-down/power-up operation.

Table 11. Modes of Operation for the AD5624R/AD5644R/

AD5664R

DB5

DB4

Operating Mode

0

0

Normal operation

Power-down modes

0

1

1 kΩ to GND

1

0

100 kΩ to GND

1

1

Three-state

When Bit DB5 and Bit DB4 are set to 0, the part works normally

with its normal power consumption of 450 μA at 5 V. However,

for the three power-down modes, the supply current falls to

480 nA at 5 V (200 nA at 3 V). Not only does the supply current

fall, but the output stage is also internally switched from the

output of the amplifier to a resistor network of known values.

This allows the output impedance of the part to be known while

the part is in power-down mode. The outputs can either be

connected internally to GND through a 1 kΩ resistor, or left

open-circuited (three-state) as shown in Figure 54.

RESISTOR

NETWORK

RESISTOR

STRING DAC

POWER-DOWN

CIRCUITRY

AMPLIFIER

Figure 56. Output Stage During Power-Down

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

other associated linear circuitry are shutdown when power-

down mode is activated. However, the contents of the DAC

register are unaffected when in power-down. The time to exit

(see Figure 39).

Table 12. 24-Bit Input Shift Register Contents for Software Reset Command

DB23 to DB22 (MSB)

DB21

DB20

DB19

DB18

DB17

DB16

DB15 to DB1

DB0 (LSB)

x

1

0

1

x

x

x

x

1/0

Don’t care

Command bits (C2 to C0)

Address bits (A2 to A0)

Don’t care

Determines software

reset mode

Table 13. 24-Bit Input Shift Register Contents of Power-Down/Power-Up Operation for the AD5624R/AD5644R/AD5664R

DB23 to

DB22

(MSB)

DB21

DB20

DB19

DB18

DB17

DB16

DB15

to DB6

DB5

DB4

DB3

DB2

DB1

DB0

(LSB)

x

1

0

0

x

x

x

x

PD1

PD0

DAC D

DAC C

DAC B

DAC A

Don’t

care

Command bits (C2 to C0)

Address bits (A2 to A0)

Don’t care

Don’t

care

Power-down

mode

Power-down/power-up channel

selection, set bit to 1 to select channel