Datasheet

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Resistor

String DAC

Powerdown

Circuitry

OUT

Amplifier

Resistor

Network

CURRENT CONSUMPTION

DAC7573

SLAS398 – SEPTEMBER 2003

Table 8. Power-Down Modes of Operation for the DAC7573

CTRL[0] MSB[7] MSB[6] OPERATING MODE

1 0 0 High Impedance Output

1 0 1 1 k Ω to GND

1 1 0 100 k Ω to GND

1 1 1 High Impedance

When (CTRL[0] = PD0 = 0), the device works normally with its normal power consumption of 150 µA at 5 V per

channel. However, for the three power-down modes, the supply current falls to 200 nA at 5 V (50 nA at 3 V). Not

only does the supply current fall but also the output stage is also internally switched from the output of the

amplifier to a resistor network of known values. This has the advantage that the output impedance of the device

is known while in power-down mode. There are three different options: The output is connected internally to GND

through a 1 k Ω resistor, a 100 k Ω resistor or left open-circuit (high impedance). The output stage is illustrated in

Figure 39 .

Figure 39. Output Stage During Power Down

All linear circuitry is shut down when the power-down mode is activated. However, the contents of the DAC

= 5 V and 5

µs for V

= 3 V. (See the Typical Curves section for additional information.)

The DAC7573 offers a flexible power-down interface based on channel register operation. A channel consists of

a single 12 bit DAC with power-down circuitry, a temporary storage register (TR) and a DAC register (DR). TR

and DR are both 14 bits wide. Two MSBs represent the power-down condition and the 12 LSBs represent data

for TR and DR. By using bits 13 and 14 of TR and DR, a power-down condition can be temporarily stored and

used just like data. Internal circuits ensure that MSB[7] and MSB[6] get transferred to TR[13] and TR[12] (DR[13]

and DR[12]) when the power-down flag (CTRL[0] = PD0) is set. Therefore, DAC7573 treats power-down

conditions like data and all the operational modes are still valid for power down. It is possible to broadcast a

power-down condition to all the DAC7573s in the system, or it is possible to simultaneously power down a

channel while updating data on other channels.

The DAC7573 typically consumes 150 µA at V

= 5 V and 125 µA at V

= 3 V for each active channel,

including reference current consumption. Additional current consumption can occur at the digital inputs if V

. For most efficient power operation, CMOS logic levels are recommended at the digital inputs to the DAC. In

power-down mode, typical current consumption is 200 nA. A delay time of 10 to 20 ms after a power-down

command is issued to the DAC is typically sufficient for the power-down current to drop below 10 µA.