The AGND pin is the bias-power and signal-ground connection for the controller. The effectiveness of the filter capacitors on the signal pins depends upon the integrity of this ground return.
- Place the decoupling capacitors for VDD, REF, CS, BUR, and P13 pins as close as possible to the device pins and AGND pin with short traces.
- The device ground and power ground should meet at the return of the current-sense resistor (RCS). Try to ensure that high frequency/high current from the power stage does not go through the signal ground.
- The thermal pad of the QFN package should be tied to the AGND pin with a short trace, and be connected to the signal ground plane with multiple vias which becomes a low-impedance ground return of external components to the AGND pin.