[SI-LIST] Re: Decoupling capacitors selection
- From: "Lakshmi Narayanan Sowrirajan, ERS-HCLTech" <lakshminarayanans@xxxxxx>
- To: chundi srikanth <chundis@xxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 1 Feb 2010 14:54:37 +0530
In case of selection of decap for an application it is very difficult to
suggest one based on previous experience without knowing the exact application.
The general understanding is to get a good clean signal and timing issue free
board (EMI/EMC tooo)it is sufficient to maintain the impedance of the plane to
a maximum of 100MHz to 200MHz under the required level (Ripple voltage
accepted/change in current dynamic in nature) above which the package and Die
capacitors needs to take care of maintaining the power plane impedance. See to
your processor data sheet for any specific recommendation on the Decap or
contact the technical support as decap selection is purely based on the Die
current profile for each operation which is not easy to be assumed. The normal
thumb rule is I dynamic = Iload/2.
Cadence or Hyperlynx PI tool might help you to a great extend in selecting
value and number of capacitors.
Thanks & Regards
Lakshminarayanan.S
9840250902
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of chundi srikanth
Sent: Monday, February 01, 2010 2:21 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Decoupling capacitors selection
Hi Friends,
Iam little bit confused in the selection of right decoupling capacitor for
my application. Iam using Freescale Coldfire MCF5208 processor. The
processors core is running at 166.66MHz and its Memory bus is operating at
83.33MHz. In my board i have a Virtex-5 FPGA for CPRI protocol and
interfaces to high-speed DAC, ADC. And i have a RF circuitry also. So my
question is Whats the main criteria for selecting decoupling capacitors for
this processor?Is there any formula to calculate the capacitance for this.
Please give me your suggestion on this. And shall i keep a capacitor per pin
or otherway?
And i have seen the MCF5208 processor evaluation board which theye are using
in Zigbee environment but they have placed very few caps of 0.1uF. Nothing
else. Can i follow the same?
Thanks & Regards
Sree
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