AD5322ARMZ datasheet(16/24 Pages) AD

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AD5302/AD5312/AD5322

Rev. D | Page 16 of 24

POWER-DOWN MODES

The AD5302/AD5312/AD5322 have very low power consump-

tion, dissipating only 0.7 mW with a 3 V supply and 1.5 mW

with a 5 V supply. Power consumption can be further reduced

when the DACs are not in use by putting them into one of three

power-down modes, which are selected by Bit 13 and Bit 12

(PD1 and PD0) of the control word. Table 7 shows how the

state of the bits corresponds to the mode of operation of that

particular DAC.

Table 7. PD1/PD0 Operating Modes

PD1

PDO

Operating Mode

Normal Operation

Power-Down (1 kΩ Load to GND)

Power-Down (100 kΩ Load to GND)

Power-Down (High Impedance Output)

When both bits are set to 0, the DACs work normally with

their normal power consumption of 300 μA at 5 V. 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

drop, but 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 part is

known while the part is in power-down mode and provides a

defined input condition for whatever is connected to the output

of the DAC amplifier. There are three different options.

•

The output is connected internally to GND through a

1 kΩ resistor,

•

The output is connected internally to GND through a

100 kΩ resistor, or

•

The output is left open-circuited (three-state).

The output stage is illustrated in Figure 33.

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

and all other associated linear circuitry are shut down when

the power-down mode is activated. However, the contents of

the registers are unaffected when in power-down. The time to

exit power-down is typically 2.5 μs for VDD = 5 V and 5 μs when

VDD = 3 V. See Figure 23 for a plot.

RESISTOR-

STRING DAC

AMPLIFIER

VOUT

POWER-DOWN

CIRCUITRY

RESISTOR

NETWORK

Figure 33. Output Stage During Power-Down

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