It is very important to establish a clean grounding scheme to ensure best performance of the device. There are three ground pins (AVSS, DVSS, CVSS) for the device’s internal power supplies and one ground reference (REFHM) for the precision reference. There are noisy grounds and quiet grounds that must be separated in the layout initially and re-joined together in a lower PCB layer. The external components (for example, bypass capacitors) must be tied to the proper grounding group if possible to keep the separation of noisy and quiet grounds apart.

• AVSS ground:
  • Bypass capacitor for these pins: VPWR, VS0, AUX0, LDOIN and TSREF
  • Package PowerPAD
• DVSS ground:
  • Bypass capacitor for DVDD
  • GPIO filter capacitor (if used). It can also connect to AVSS ground plane, if needed.
• CVSS ground:
  • Bypass capacitor for CVDD
  • Bypass capacitors for COMHP/N, and COMLP/N
• REFHM ground:
  • Bypass capacitor for REFHP
  • If possible, separate out REFHM from AVSS on the signal connection layer and re-connect REFHM to AVSS ground plane in the lower layer.

Even on a PCB layer that is mainly for signal routing, it is good practice to pour have a small island of ground pour if possible to provide a low-impedance ground, rather than simply a via through the ground trace to an lower ground plane.

Figure 11-1 Grounding Layout Consideration