REV. 0

AD5301/AD5311/AD5321

–13–

POWER-DOWN MODES

The AD5301/AD5311/AD5321 have very low power consump-

tion, dissipating typically 0.36 mW with a 3 V supply and

0.75 mW with a 5 V supply. Power consumption can be further

reduced when the DAC is not in use by putting it into one of

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

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

of the bits corresponds to the mode of operation of the DAC.

Table I. PD1/PD0 Operating Modes

PD1

PD0

Operating Mode

0

0

Normal Operation

0

1

Power-Down (1 k

Ω Load to GND)

1

0

Power-Down (100 k

Ω Load to GND)

1

1

Power-Down (Three-State Output)

The software power-down modes programmed by PD0 and

PD1 may be overridden by the

PD pin on the 8-pin version.

Taking this pin low puts the DAC into three-state power-down

mode. If

PD is not used it should be tied high.

When both bits are set to 0, the DAC works normally with its

normal power consumption of 150

µA at 5 V, while 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 con-

nected internally to GND through a 1 k

Ω resistor, a 100 kΩ

resistor or it is left open-circuited (Three-State). Resistor toler-

ance =

±20%. The output stage is illustrated in Figure 30.

AMPLIFIER

POWER-DOWN

CIRCUITRY

RESISTOR

NETWORK

RESISTOR-

STRING DAC

Figure 30. Output Stage During Power-Down

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

all other associated linear circuitry are all shut down when the

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

DAC register are unchanged when in power-Down. The time to

exit power-down is typically 2.5

µs for V

µs when

APPLICATIONS

USING REF19x AS A POWER SUPPLY

Because the supply current required by the AD5301/AD5311/

AD5321 is extremely low, the user has an alternative option

to use a REF19x voltage reference (REF195 for +5 V or REF193

for +3 V) to supply the required voltage to the part, see Fig-

ure 31.

AD5301/

AD5311/

AD5321

2-WIRE

SERIAL

INTERFACE

SDA

SCL

+15V

+5V

150 A TYP

REF195

Figure 31. REF195 as Power Supply to AD5301/AD5311/

AD5321

This is especially useful if the power supply is quite noisy or if

the system supply voltages are at some value other than +5 V or

+3 V (e.g., +15 V). The REF19x will output a steady supply

voltage for the AD5301/AD5311/AD5321. If the low dropout

REF195 is used, the current it needs to supply to the AD5301/

AD5311/AD5321 is 150

µA. This is with no load on the output

of the DAC. When the DAC output is loaded, the REF195 also

needs to supply the current to the load.

The total current required (with a 2 k

Ω load on the DAC

output and full scale loaded to the DAC) is:

150

µA + (5 V/2 kΩ) = 2.65 mA

The load regulation of the REF195 is typically 2 ppm/mA which

results in an error of 5.3 ppm (26.5

µV) for the 2.65 mA current

drawn from it. This corresponds to a 0.00136 LSB error.

BIPOLAR OPERATION USING THE AD5301/AD5311/

AD5321

The AD5301/AD5311/AD5321 has been designed for single-

supply operation but a bipolar output range is also possible

using the circuit in Figure 32. The circuit below will give an

output voltage range of

±5 V. Rail-to-rail operation at the am-

plifier output is achievable using an AD820 or an OP295 as the

output amplifier.

+5V

–5V

AD820/

OP295

2-WIRE

SERIAL

INTERFACE

+5V

AD5301/

AD5311/

AD5321

10 F

0.1 F

R1 = 10k

5V

R2 = 10k

Figure 32. Bipolar Operation with the AD5301/AD5311/

AD5321