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DAC7742 Datasheet(PDF) 16 Page - Texas Instruments |
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DAC7742 Datasheet(HTML) 16 Page - Texas Instruments |
16 / 22 page DAC7742 16 SBAS256A www.ti.com LAYOUT A precision analog component requires careful layout, adequate bypassing, and clean, well-regulated power supplies. The DAC7742 offers separate digital and analog supplies, as 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 important it will become to separate the analog and digital ground and supply planes at the device. Since the DAC7742 has both analog and digital ground pins, return currents can be better controlled and have less effect on the DAC output error. Ideally, AGND would be connected directly to an analog ground plane and DGND to the digital ground plane. The analog ground 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 voltages applied to VCC and VSS should be well regulated and low noise. Switching power supplies and DC/DC con- verters 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. In addition, a 1 µF to 10µF bypass capacitor in parallel with a 0.1 µF bypass capacitor is strongly recommended for each supply input. 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 analog supplies, removing any high frequency noise components. NOISE PERFORMANCE Increased noise performance of the DAC output can be achieved by filtering the voltage reference input to the DAC7742. Figure 10 shows a typical internal reference filter schematic. A low-pass filter applied between the REFOUT and REFIN pins can increase noise immunity at the DAC and output amplifier. The REFOUT pin can source a maximum of 50 µA so care should be taken in order to avoid overloading the internal reference output . 43 44 45 46 47 48 (Other Connections Omitted for Clarity) RSTSEL REFEN REF OUT REFADJ REF IN NC 100k Ω 1 µF FIGURE 10. Internal Reference Filter. |
Similar Part No. - DAC7742_15 |
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Similar Description - DAC7742_15 |
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