If the analog ground (AGND) and power ground (PGND) pins are separated on the board, the power stage and related components should be terminated or bypassed to the power ground. Signal components of TPS40425 device should be terminated or bypassed to the analog ground. Connect the thermal pad of the device to power ground plane through sufficient vias. Connect AGND and PGND pins of the device to the thermal pad directly. The connection between AGND pin and thermal pad serves as the only connection between analog ground and power ground.
If one common ground is used on the board, the TPS40425 device and related components must be placed on a noise quiet area which is isolated from fast switching voltage and current paths.
Maintain placement of signal components and regulator bypass capacitors local to the TPS40425 device. Place them as close as possible to the terminals to which they are connected. These components include the feedback resistors, frequency compensation, the RT resistor, ADDR0 and ADDR1 resistors, as well as bypass capacitors for BP3, BP5, and VDD.
The VSNSx and GSNSx must be routed as a differential pair on noise quiet area.
The CSxP and CSxN must be routed as a differential pair on noise quiet area. Place a capacitor with a value or 0.22-uF or larger between CSxP and CSxN. Placed that capacitor as close to the TPS40425 device and as possible. Place a 0.1-uF capacitor between CSxN and ground, and place it close to the TPS40425 device.
Place the thermal transistor close to the inductor. Place a bypass capacitor with a value of 1 nF or larger close to the transistor. Use a separate ground trace for the transistor. Place another 1-nF bypass capacitor close to TSNSx terminal.