Datasheet

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OUTPUT VOLTAGE STABILITY
SETTLING TIME AND OUTPUT GLITCH PERFORMANCE
USING REF02 AS A POWER SUPPLY FOR DAC8571
REF02
15 V
5 V
V
DD
, V
ref
A0
SCL
SDA
2-Wire
l
2
C
Interface
V
OUT
= 0 V to 5 V
DAC8571
160 A 
5 V
5 k
 1.16 mA
LAYOUT
DAC8571
SLAS373A – DECEMBER 2002 – REVISED JULY 2003
The DAC8571 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 of each channel 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. Combined with good dc noise
performance and true 16-bit differential linearity, the DAC8571 becomes a perfect choice for closed-loop control
applications.
Settling time to within the 16-bit accurate range of the DAC8571 is achievable within 10 µs for a full-scale code
change at the input. Worst case settling times between consecutive code changes is typically less than 2 µs,
therefore, the update rate is limited by the I
2
C interface for digital input signals changing code-to-code. For
full-scale output swings, the output stage of each DAC8571 channel typically exhibits less than 100-mV
overshoot and undershoot when driving a 200-pF capacitive load. Code-to-code change glitches are extremely
low (~10 µV) given that the code-to-code transition does not cross an Nx4096 code boundary. Due to internal
segmentation of the DAC8571, code-to-code glitches occur at each crossing of an Nx4096 code boundary.
These glitches can approach 100 mVs for N = 15, but settle out within ~2 µs.
Due to the extremely low supply current required by the DAC8571, a possible configuration is to use a REF02
5-V precision voltage reference to supply the required voltage to the DAC8571's supply input as well as the
reference input, as shown in Figure 33 . 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. The REF02 outputs a steady supply voltage for the DAC8571.
If the REF02 is used, the current it needs to supply to the DAC8571 is 160- µA typical and 225- µA max for V
DD
=
5 V. When a DAC output is loaded, the REF02 also needs to supply the current to the load. The total typical
current required (with a 5-k Ω load on a given DAC output) is:
Figure 33. REF02 as a Power Supply
The load regulation of the REF02 is typically 0.005%/mA, which results in an error of 290 µV for a 1.16-mA
current drawn. This corresponds to a 3.82 LSB error for a 0-V to 5-V output range.
A precision analog component requires careful layout, adequate bypassing, and clean, well-regulated power
supplies.
The power applied to V
DD
and V
REF
should be well regulated and low noise. Switching power supplies and dc/dc
converters often has high-frequency glitches or spikes riding on the output voltage. In addition, digital
components can create similar high-frequency spikes as their internal logic switches states. This noise easily
couples into the DAC output voltage through various paths between the power connections and analog output.
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