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Resistor

String DAC

Powerdown

Circuitry

Amplifier

Resistor

Network

CURRENT CONSUMPTION

DRIVING RESISTIVE AND CAPACITIVE LOADS

OUTPUT VOLTAGE STABILITY

DAC7571

SLAS374A – FEBRUARY 2003 – REVISED JANUARY 2004

Table 2. Modes of Operation for the DAC7571

PD1

PD0

OPERATING MODE

0

0

Normal Operation

0

1

1k

Ω to AGND, PWD

1

0

100k

Ω to AGND, PWD

1

1

High Impedance, PWD

When both bits are set to 0, the device works normally with normal power consumption of 150 µA at 5V.

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

the supply current fall 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 device is known while in

power-down mode. There are three different options: The output is connected internally to AGND through a 1 k

Ω

resistor, a 100 k

Ω resistor, or it is left open-circuited (high impedance). The output stage is illustrated in

Figure 46.

Figure 46. Output Stage During Power-Down

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

recommended at the digital inputs to the DAC. In power-down mode, typical current consumption is 200 nA. Ten

to 20 ms after a power-down command is issued, the power-down current typically drops below 10 mA.

The DAC7571 output stage is capable of driving loads of up to 1000 pF while remaining stable. Within the offset

and gain error margins, the DAC7571 can operate rail-to-rail when driving a capacitive load. Resistive loads of 2

k

Ω can be driven by the DAC7571 while achieving a typical load regulation of 1%. As the load resistance drops

below 2 k

Ω, the load regulation error increases. When the outputs of the DAC are driven to the positive rail under

resistive loading, the PMOS transistor of each Class-AB output stage can enter into the linear region. When this

occurs, the added IR voltage drop deteriorates the linearity performance of the DAC. This may occur within

approximately the top 20 mV of the DAC's digital input-to-voltage output transfer characteristic.

The DAC7571 exhibits excellent temperature stability of 5 ppm/

°C typical output voltage drift over the specified

temperature range of the device. This enables the output voltage to stay within a

±25 µV window for a ±1°C

ambient temperature change. Good power-supply rejection ratio (PSRR) performance reduces supply noise

and true 12-bit differential linearity, the DAC7571 becomes a perfect choice for closed-loop control applications.

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