Datasheet

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USING REF02 AS A POWER SUPPLY FOR DAC6574

REF02

15 V

5 V

1.6 mA

SCL

SDA

Interface

OUT

= 0 V to 5 V

DAC6574

LAYOUT

DAC6574

SLAS408 – DECEMBER 2003

APPLICATION INFORMATION (continued)

external reference to the device. Due to low power consumption of DAC6574, load regulation errors are

negligible. In order to avoid excess power consumption at the Schmitt-triggered inputs of DAC6574, the precision

reference voltage should be close to the I

C bus pullup voltage. For 3-V, 3.3-V and 5-V I

C bus pullup voltages,

REF2930, REF2933 and REF02 precision voltage references are recommended respectively. These precision

voltage references can be used to supply power for multiple devices on a system.

Due to the extremely low supply current required by the DAC6574, a possible configuration is to use a REF02

+5 V precision voltage reference to supply the required voltage to the DAC6574 supply input as well as the

reference input, as shown in Figure 40 . 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 DAC6574.

If the REF02 is used, the current it needs to supply to the DAC6574 is 600 µA typical and 900 µA max for

= 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 single DAC output) is:

600 µA + (5 V / 5 k Ω) = 1.6 mA

The load regulation of the REF02 is typically 0.005%/mA, which results in an error of 400 µV for 1.6 mA of

current drawn from it. This corresponds to a 0.08 LSB error for a 0-V to 5-V output range.

Figure 40. REF02 Power Supply

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

supplies.

For best performance, the power applied to V

must be well-regulated and low noise. Switching power supplies

and dc/dc converters 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

must be connected to a positive 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, a 1- µF to 10- µF

capacitor in parallel with a 0.1- µF bypass capacitor is 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.