11.1 Layout Guidelines

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

The DAC8x11 offers single-supply operation; it will often be used in close proximity with digital logic, microcontrollers, microprocessors, and digital signal processors. The more digital logic present in the design and the higher the switching speed, the more difficult it will be to achieve good performance from the converter.

Because of the single ground pin of the DAC8x11, all return currents, including digital and analog return currents, must flow through the GND pin. Ideally, GND would be connected directly to an analog ground plane. This plane would be separate from the ground connection for the digital components until they were connected at the power entry point of the system.

The power applied to AV_DD should 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 the internal logic switches state. This noise can easily couple into the DAC output voltage through various paths between the power connections and analog output. This condition is particularly true for the DAC8x11, as the power supply is also the reference voltage for the DAC.

As with the GND connection, AV_DD 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, TI strongly recommends the 1 μF to 1 μF and 0.1 μF bypass capacitors. 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.

11.2 Layout Example

Figure 90. Recommended Layout