Datasheet

V X
OUT
Amplifier
Resistor
String
DAC
Power-Down
Circuitry
Resistor
Network
DAC7568
DAC8168
DAC8568
SBAS430D –JANUARY 2009–REVISED MAY 2012 www.ti.com
POWER-DOWN MODES When both the PD0 and PD1 bits are set to '0', the
device works normally with its typical current
The DAC7568, DAC8168, and DAC8568 have two
consumption of 1.25mA at 5.5V. The reference
separate sets of power-down commands. One set is
current is included with the operation of all eight
for the DAC channels and the other set is for the
DACs. However, for the three power-down modes,
internal reference. For more information on powering
the supply current falls to 0.18μA at 5.5V (0.10μA at
down the reference, see the Enable/Disable Internal
3.6V). Not only does the supply current fall, but the
Reference section.
output stage also switches internally from the output
of the amplifier to a resistor network of known values.
DAC Power-Down Commands
The advantage of this switching is that the output
The DAC7568, DAC8168, and DAC8568 use four
impedance of the device is known while it is in power-
modes of operation. These modes are accessed by
down mode. As described in Table 12, there are
setting control bits C3, C2, C1, and C0, and power-
three different power-down options. V
OUT
can be
down register bits DB8 and DB9. The control bits
connected internally to GND through a 1kΩ resistor, a
must be set to '0100'. Once the control bits are set
100kΩ resistor, or open circuited (High-Z). The output
correctly, the four different power down modes are
stage is shown in Figure 124. In other words, DB27,
software programmable by setting bits DB8 and DB9
DB26, DB25, and DB24 = '0100' and DB9 and DB8 =
in the control register. Table 11 and Table 12 shows
'11' represent a power-down condition with High-Z
how to control the operating mode with data bits PD0
output impedance for a selected channel. DB9 and
(DB8), and PD1 (DB9).
DB8 = '01' represents a power-down condition with
1kΩ output impedance, and '10' represents a power-
Table 12. DAC Operating Modes
down condition with 100kΩ output impedance.
PD1 PD0
(DB9) (DB8) DAC OPERATING MODES
0 0 Power up selected DACs
0 1 Power down selected DACs 1kΩ to GND
1 0 Power down selected DACs 100kΩ to GND
1 1 Power down selected DACs High-Z to GND
The DAC7568, DAC8168, and DAC8568 treat the
power-down condition as data; all the operational
modes are still valid for power-down. It is possible to
broadcast a power-down condition to all the
DAC8568, DAC8168, DAC7568s in a system. It is
also possible to power-down a channel and update
Figure 124. Output Stage During Power-Down
data on other channels. Furthermore, it is possible to
write to the DAC register/buffer of the DAC channel
All analog channel circuits are shut down when the
that is powered down. When the DAC channel is then
power-down mode is exercised. However, the
powered up, it will power up to this new value (see
contents of the DAC register are unaffected when in
the Operating Examples section).
power down. By setting both bits, DB8 and DB9, to
different values, any combination of DAC channels
can be powered down or powered up. If a DAC
channel is being powered up from a previously power
down situation, this DAC channel powers up to the
value in its DAC register. The time required to exit
power-down is typically 2.5μs for AV
DD
= 5V, and 4μs
for AV
DD
= 3V. See the Typical Characteristics for
more information.
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