SI8250 Datasheet, PDF (21/30 Pages) Silicon Laboratories – DIGITAL POWER CONTROLLER

Si8250/1/2
6. Layout Considerations
The mixed-signal nature of the Si8250/1/2 mandates clean bias supplies and ground returns. It is best to provide
separate ground planes for analog, digital and power switch returns. These planes should tie together at only one
point to eliminate the possibility of circulating ground currents.
For best performance, the VDD supply should be decoupled from the main supply. The LQFP-32 package provides
the best noise performance because it has separate analog and digital VDD and ground inputs (AVDD, AGND). As
shown in Figure 9, the AVDD is decoupled by a filter consisting of a 1 Ω resistor in series with a 500 mA, 40 Ω
ferrite bead and a parallel combination of a 10 uF with a 0.1 uF high-frequency bypass capacitor. All connections
should be kept as short as possible. The VDDA and GNDA should be connected into their respective ground
planes. The QFN-28 package shares analog and digital power with ground on the same pins. Power supply
decoupling is shown in Figure 10. Again, all connections should be kept as short as possible.
Ferrite bead
500 mA, 40 Ω
1Ω
2.5 V
10 uF
0.1 uF
Keep trace _AGND
lengths as short
as possible
AVDD
DVDD
Si8250/1/2
AGND
DGND
10 uF
0.1 uF
Figure 9. Power Supply Connections for LQFP-32 Package
10 uF
0.1 uF
Ferrite bead
500 mA, 40 Ω
1Ω
VDD
Si8250/1/2
2.5 V
Keep trace
lengths as short
as possible
GND
Figure 10. Power Supply Connections for QFN-28 Package
Preliminary Rev. 0.8
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