[SI-LIST] Re: Output Capacitor of a switching Regulato
- From: ANAND KURIAKOSE <Anand.Kuriakose@xxxxxxxxxx>
- To: vel_ss@xxxxxxxxx
- Date: Thu, 1 Aug 2002 21:01:23 -0700
Hi Senthil,
Basically what i am doing is substituting VL/Lo in place of di/dt in
the equation, where VL is the smallest of the voltages across the output
inductor and Lo is the output inductor value. And this is what the
switching regulator's datahseet also says and this puts us in a safe Cmin.
The design is for the chipset and the chipset manufacturer hasnt specified
the di/dt specification.
Regards,
Anand.
From: Senthil S Velmurugan <vel_ss@xxxxxxxxx> on 08/02/2002 01:00
AM
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Subject: [SI-LIST] Re: Output Capacitor of a switching
Regulato
Hi Anand,
Can you let me know how you have arrived at di/dt
value for the equation ?
I see, say, some CPU's requirement for X-Amp/uS
How much you want to have VRM or switcher bulk cap to
supply those X-Amp/uS ?.
I think the X-Amps is supplied by a combination of
package, plane and decoupling caps and
bulk cap follows to fill those, At what rate is my
question in other way.
Hi Larry,
I think this need to be clarified to calculate Cmin,
but I do not see any info on this subject other than
using a tool(ex,. Ansoft)to model the complete
switcher
with package parasitic of CPU which you may not know
unless you use TDR to extract those parameters,
these models are not given out by any CPU vendor.
Tools to reduce plane impedance are being used to
reduce the plane impedance below Z target by choosing
an huge array of caps. Caveat being, What is the roll
up of impedance curve at what frequency depends on the
processor's working pattern and freq'y, this pattern
needs to be known to reduce the amount of caps
suggested by the tool.
Can you through some more light on this and a suggest
an optimum way to ensure right Bulk cap for a on board
regulator in the first time without doing any
simulation or without building the board and measure
it approach.
VRM modules have the luxury of holding 10 caps on a
vertical board but not on a small form factor embedded
mother boards is another challenge and no room to have
liberal approach.
Thanks
Senthil
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