Supply for RVDD (Internal RAM Supply)

Hi Chandra Shekhar

If you are planning to run the device at 375 MHz, and you have devices that can run at 456 MHz/375 MHz (suffix 4/3 ) you can keep the RVDD at 1.2V. Please keep in mind that if you plan to use voltage scaling (say run the device at 1.1 or 1.0 V then please make sure RVDD is tied with the other static supplies etc, as mentioned in the datasheet)

chandrashekhar mishra said:

Does RVDD depend on version or frequency of operation ?

Overall it depends on the frequency of operations ( please look at the Recommended Operating Conditions , Section 5.2 , last rows in the datasheet) , but you also need to make sure you have the revision of the device that allows you to run it at speeds greater then 300 MHz.

Let us know if you have more questions.

Regards

Mukul

Hi Mukul Bhatnagar,

I just noticed this thread, so I wouldn't start a new one. I am now designing a board with the C6746, and I'm also confused a bit with the RVDD voltage. We design with the 456 MHz version, but we want to keep the option of either using it at 375 MHz (or even slower), or actually populate a 375 MHz version. We will also use voltage scaling to keep the power consumption minimal, because we are running on a battery. The DSP needs to run only intermittently at full speed and even then only for a short time. Our main concern is the consumption in the idle periods. I can't decide now how the RAM voltage needs to be scaled.

1. RVDD is at least 1.2V, while the processor runs at or slower than 375 MHz (regardless if it's a 456 MHz version or not). When the processor is running at higher than 375 MHz, RVDD must be boosted to 1.3V, while keeping the rest of the static voltages at 1.2V

2. RVDD can always run at 1.3V, if the 456 MHz version is soldered on the board, regardless of the actual speed. In this case however, I don't know how much the current consumption is increased when the processor runs at low frequencies. I.e. how much more does the RAM consume at 1.3V compared to if we decreased its voltage (when possible) back to 1.2V?

My question is: is option 1 possible? Do we gain power with option 1 (i.e. by lowering not only the CVDD to 1.0V, but the RVDD to 1.2, as well.)?

Thank you very much in advance!

Best regards,

Paul

Hi Paul

Please see if the following post and response from Clay Turner helps clarifies the legal combinations on CVDD vs RVDD

http://e2e.ti.com/support/dsp/omap_applications_processors/f/42/p/92507/324832.aspx#324832

Regarding your question on power consumption, you should be able to get the power consumption for RVDD from the power estimation spreadsheet for OMAPL138

You can download it from the following wiki link

http://processors.wiki.ti.com/index.php/OMAP-L138_Power_Consumption_Summary

Column Z provides the RVDD current consumption and you can see the changes in consumption for 1.3V vs 1.2V RVDD

Hope this helps.

Let us know if you have additional questions.

Regards

Mukul

Please note that even though the forum post I cross linked is for OMAPL138, this applies to c6748/46 too as they are DSP only parts from the same design family.

Regards

Mukul