Datasheet

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Resistor
String DAC
Powerdown
Circuitry
V
OUT
Amplifier
Resistor
Network
CURRENT CONSUMPTION
DRIVING RESISTIVE AND CAPACITIVE LOADS
OUTPUT VOLTAGE STABILITY
DAC7571
SLAS374C – FEBRUARY 2003 – REVISED MAY 2006
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
register are unaffected when in power-down. The time required to exit power down is typically 2.5 µs for AV
DD
=
5 V and 5 µs for AV
DD
= 3 V. See the Typical Characteristics for more information.
The DAC7571 typically consumes 150 µA at V
DD
= 5 V and 120 µA at V
DD
= 3 V. Additional current consumption
can occur due to the digital inputs if V
IH
<< V
DD
. 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. 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
present on V
DD
from appearing at the outputs to well below 10 µV-s. Combined with good dc noise performance
and true 12-bit differential linearity, the DAC7571 becomes a perfect choice for closed-loop control applications.
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