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Explorer
Explorer
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Registered: ‎07-10-2013

V7 XPE BRAM Power

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I'm running the XPE speadsheet (v 2014.1) for an XC7VX330T and looking at a theoretical BRAM situation of: 350 RAMB36SDP, 50% toggle rate; Port A clocked at 200MHz, 100% enable rate, 72 bits wide, write-first mode; Port B clocked at 200MHz, 100% enable rate, 72 bits wide, read-first mode.

 

The power cited for Vccbram is 0.166W, while the power cited for Vccint is 4.277W.

 

It was my understanding that Vccbram "supplied the power for the BRAMs", i.e., rather than Vccint!?!

 

XC7VX330T
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Explorer
Explorer
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Registered: ‎07-10-2013

Anirudh,

 

Thanks for the link, etc.

 

My point, I suppose, is that if the vast majority of power for the BRAMs is not coming from Vccbram, then it might be better referrred to as Vccbram_aux, or something similar.  And the documentation (such as UG473) would do well to point out that only a small portion of the current/power needed for the BRAMs is actually provided by Vccbram, with most provided by Vccint.  Statements (p.9) such as "The new external power supply VCCBRAM is used to power the block RAM memory

cells" give a completely misleading impression of the actual situation.

 

Thanks again :)

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Xilinx Employee
Xilinx Employee
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Registered: ‎07-31-2012

Hi,

 

VCCINT and VCCBRAM both should be needed for powering the BRAM's. Check pg 47 of this link - http://www.xilinx.com/support/documentation/sw_manuals/xilinx14_7/ug440-xilinx-power-estimator.pdf for more information on VCCINT and VCCBRAM.

 

Check Pg 68 for BRAM power estimates in terms of VCCINT and VCCBRAM.

Thanks,
Anirudh

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Explorer
Explorer
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Registered: ‎07-10-2013

Anirudh,

 

Thanks for the link, etc.

 

My point, I suppose, is that if the vast majority of power for the BRAMs is not coming from Vccbram, then it might be better referrred to as Vccbram_aux, or something similar.  And the documentation (such as UG473) would do well to point out that only a small portion of the current/power needed for the BRAMs is actually provided by Vccbram, with most provided by Vccint.  Statements (p.9) such as "The new external power supply VCCBRAM is used to power the block RAM memory

cells" give a completely misleading impression of the actual situation.

 

Thanks again :)

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Xilinx Employee
Xilinx Employee
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Registered: ‎10-11-2007

Vccbram power the memory cells in the BRAM only. The BRAM logic is powered by Vccint.  But at the end of the day you probably want to connect Vccbram to Vccint anyway. Also, you have to consider standby current on Vccint and any other logic you have running on Vccint. So it's not all Vccint current consumed by the BRAM.

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