Datasheet

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APPLICATIONS

USING REF02 AS A POWER SUPPLY FOR THE DAC7571

REF02

15 V

5 V

1.14 mA

SCL

SDA

Interface

OUT

= 0 V to 5 V

DAC7571

LAYOUT

DAC7571

SLAS374C – FEBRUARY 2003 – REVISED MAY 2006

Due to the extremely low supply current required by the DAC7571, a possible configuration is to use a REF02

+5V precision voltage reference to supply the required voltage to the DAC7571's supply input as well as the

reference input, as shown in Figure 47 . 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 will output a steady supply voltage for the

DAC7571. If the REF02 is used, the current it needs to supply to the DAC7571 is 150 µA typical and 200 µA

max for V

= 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 mW load on a given DAC output) is: 135 µA + (5 mW/5 V) = 1.14 mA.

The load regulation of the REF02 is typically (0.005% ×V

)/mA, which results in an error of 285 mV for the 1.14

mA current drawn from it. This corresponds to a 0.2 LSB error for a 0 V to 5 V output range.

Figure 47. REF02 as Power Supply to DAC7571

A precision analog component requires careful layout, adequate bypassing, and clean, well-regulated power

supplies.

The power applied to V

should be well regulated and low noise. Switching power supplies and DC/DC

converters will often have 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 can

easily couple into the DAC output voltage through various paths between the power connections and analog

output.

As with the GND connection, V

should be connected to a +5 V power supply plane or trace that is separate

from the connection for digital logic until they are connected at the power entry point. In addition, the 1 µF to 10

µF and 0.1 µF bypass capacitors are strongly recommended. In some situations, additional bypassing may be

required, such as a 100 µF electrolytic capacitor or even a Pi filter made up of inductors and capacitors—all

designed to essentially low-pass filter the +5 V supply, removing the high-frequency noise.

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