DM9161B
Layout Guide
Version: DM9161B-LG-V10
5
August 9, 2007
2. Power Supply Decoupling Capacitors
•
Place all the decoupling capacitors for all power supply pins as close as possible to the power pads of the
DM9161B (no more than 2.5mm from the above mentioned pins). The recommended decoupling capacitor
is 0.1µF or 0.01µF.
•
The PCB layout and power supply decoupling should provide sufficient decoupling to achieve the following
when measured at the device:
(1) All DVDDs and AVDDs should be within 50m Vpp of each other,
(2) All DGNDs and AGNDs should be within 50m Vpp of each other.
(3) The resultant AC noise voltage measured across each DVDD/DGND set and AVDD/AGND set should be
less than 100m Vpp.
•
The 0.1-0.01µF decoupling capacitor should be connected between each DVDD/DGND set and
AVDD/AGND set and be placed as close as possible to the pins of DM9161B. The conservative approach is
to use two decoupling capacitors on each DVDD/DGND set and AVDD/AGND set. One 0.1µF is for low
frequency noise, and the other 0.01µF is for high frequency noise on the power supply.
•
The AVDD connection to the transmit center tap of the magnetic has to be well decoupled to minimize
common mode noise injection from the power supply into the twisted pair cable. It is recommended that a
0.01µF decoupling capacitor should be placed between the center tap AVDD to AGND ground plane. This
decoupling capacitor should be placed as close as possible to the center tap of the magnetic.10 uF or 47 uF
Capacitor should be connected between each AVDD and AGND.
Figure 2
