ZHCSHR4F January 2009 – April 2018 DAC7568 , DAC8168 , DAC8568
PRODUCTION DATA.
The DAC7568, DAC8168, and DAC8568 use four modes of operation. These modes are accessed by setting control bits C3, C2, C1, and C0, and power-down register bits DB8 and DB9. The control bits must be set to '0100'. Once the control bits are set correctly, the four different power down modes are software programmable by setting bits DB8 and DB9 in the control register. and Table 4 shows how to control the operating mode with data bits PD0 (DB8), and PD1 (DB9).
PD1
(DB9) |
PD0
(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 data on other channels. Furthermore, it is possible to write to the DAC register/buffer of the DAC channel that is powered down. When the DAC channel is then powered up, it will power up to this new value (see the Operating Examples section).
When both the PD0 and PD1 bits are set to '0', the device works normally with its typical current consumption of 1.25mA at 5.5V. The reference current is included with the operation of all eight DACs. However, for the three power-down modes, the supply current falls to 0.18μA at 5.5V (0.10μA at 3.6V). Not only does the supply current fall, but the output stage also switches internally from the output of the amplifier to a resistor network of known values.
The advantage of this switching is that the output impedance of the device is known while it is in power-down mode. As described in Table 4, there are three different power-down options. VOUT can be connected internally to GND through a 1kΩ resistor, a 100kΩ resistor, or open circuited (High-Z). The output stage is shown in Figure 124. In other words, DB27, DB26, DB25, and DB24 = '0100' and DB9 and DB8 = '11' represent a power-down condition with High-Z output impedance for a selected channel. DB9 and DB8 = '01' represents a power-down condition with 1kΩ output impedance, and '10' represents a power-down condition with 100kΩ output impedance.
All analog channel circuits are shut down when the power-down mode is exercised. However, the contents of the DAC register are unaffected when in 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 AVDD = 5V, and 4μs for AVDD = 3V. See the Typical Characteristics section for more information.