[SI-LIST] Re: need of voltage regulator for SPARTAN-III VCCINT supply
- From: steve weir <weirsp@xxxxxxxxxx>
- To: anshul_johari@xxxxxxxxx, si-list@xxxxxxxxxxxxx
- Date: Wed, 15 Oct 2003 13:35:24 -0700
Anshul, a well designed, synchronously rectified switcher may reach about
80% efficiency at those power levels, so input power would be 4.5W. A
linear regulator will only yield an efficiency of Vo/Vin which in your case
means 33%, or an input power of 10.8W, more than twice that of the
switcher. The losses in the LDO at the battery starting voltage will be
7-8X that of the switcher and that heat will have to be dissipated
somewhere. The attractions of linear LDO's are that they are cheaper and
simpler than SMPS regulators. But, they can quickly get bigger than a
switcher when the heat sink area gets to be too much.
For an SMPS approach the size is a tradeoff between allocating real estate
to the energy storage components, or to additional switches and cost for a
poly phase design. You haven't mentioned what your cost sensitivity
is. In your PDS design, you will also need to consider the turn-on current
surge of Xilinx Virtex family FPGAs. I think you need to ask for help
either from apps engineers at Linear Tech, Maxim, NS, TI or whoever's
regulators/controllers you are considering, or find a suitable consultant.
Regards,
Steve.
At 10:56 PM 10/14/2003 -0700, anshul wrote:
>hi all
>yesterday i had put up the question regarding the
>requirment of LDO for 1.2 volt regulator.
>now i m re defining my Question. Actully i have to
>design a prototype board with Spartan-III Fpga and my
>current requirment is 3 A min. Spartan-III FPGA
>requires 1.2 volt power supply . for this requirment i
>require one good regulator with 3.6 volt input and 1.2
>volt output.this prototype board is battery powered.
>please suggess me which type of regulator should i use
>either a LDO or a switching regulator. Board Size is a
>constraint in my design. i will be very greatfull if
>some one please give me the comparison between LDO
>and Switching Regulator for this requirment.
>thanks
>regars
>anshul
>
>
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