Datasheet

AD5624/AD5664
Rev. 0 | Page 17 of 24
SOFTWARE RESET
The AD5624/AD5664 contain a software reset function.
Command 110 is reserved for the software reset function (see
Table 7). The software reset command contains two reset modes
that are software programmable by setting Bit DB0 in the
control register.
Table 9 shows how the state of the bit
corresponds to the software reset modes of operation of the
devices.
Table 9. Software Reset Modes for the AD5624/AD5664
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
POWER-DOWN MODES
The AD5624/AD5664 contain four separate modes of operation.
Command 100 is reserved for the power-down function (see
Table 7). These modes are software programmable by setting two
bits (DB5 and DB4) in the control register.
Table 10 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 is powered up by setting Bit DB5 and
Bit 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 11 for contents of the
input shift register during the power-down/power-up operation.
Table 10. Modes of Operation for the AD5624/AD5664
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 both bits are set to 0, the parts work normally with their
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 or 100 kΩ resistor, or left open-circuited (three-state)
(see
Figure 34).
RESISTOR
NETWORK
V
OUT
RESISTOR
STRING DAC
POWER-DOWN
CIRCUITRY
AMPLIFIER
05943-037
Figure 34. Output Stage During Power-Down
The bias generator, the output amplifier, the resistor string, and
other associated linear circuitry are shut down when power-
down mode is activated. However, the contents of the DAC
register are unaffected when in power-down. The time to exit
power-down is typically 4 µs for V
DD
= 5 V and for V
DD
= 3 V
(see
Figure 21).
Table 11. 24-Bit Input Shift Register Contents of Power-Down/Power-Up Operation
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