C6678 Unused DDR3 Configuration

Bill Bard

As mentioned in another post, we are not using the DDR3 portion of the C6678. It was stated that the DVDD15 power input pins can be left floating.

We have found out that for internal clocking needs of the C6678, the DDRCLK input to the DSP must be active.

Does the AVDDA2 power input provide all the necessary power required for the DDR3 internal clocking needs?

Is the DVDD15 only used for I/O buffers but not the internal clocking and that is why those pins can be left floating?

Do these floating DVDD15 pins require any bypass capacitors?

One final question, should the PTV15 pin, normally a 45.3 ohm resistor to VSS, still be connected? If so, what is the approximate current through the resistor?

Thanks!

Bill

over 9 years ago

0 Bill Taboada over 9 years ago

TI__Mastermind 42545 points

Hi Bill,

The AVDDA2 power input provides the power to the DDR PLL. The DDR PLL must be powered to provide a clock to the DDR subsection which is needed to properly reset the DDR subsection. The DVDD15 voltage is only used for the DDR3 IOs. If DVDD15 is left floating, no bypass capacitors are needed.

I will check on the PTV resistor.

Regards,

Bill

0 Bill Bard over 9 years ago in reply to Bill Taboada

Prodigy 60 points

Hi Bill,

Senthil replied to an earlier question at

https://e2e.ti.com/support/dsp/c6000_multi-core_dsps/f/639/p/470373/1717327#1717327

that the DVDD15 voltage is required. It appears that perhaps older versions allowed the interfaces to be powered down but now that's not the case?

Could you verify this?

Thanks!

Bill

0 Bill Taboada over 9 years ago in reply to Bill Bard

TI__Mastermind 42545 points

Hi Bill,

That is correct. After checking with the design team and discussing the issue with Senthil we have confirmed that KeyStone parts do require the DVDD15 voltage even if the DDR3 interface is not used. The DDRCLK reference clock is also required to allow the DDR3 subsystem to initialize correctly after reset. If the DDRCLK is not present in the design, the DDR3 subsystem will be left in an unknown state which can cause increased power consumption.

Regards,

Bill

0 Bill Bard over 9 years ago in reply to Bill Taboada

Prodigy 60 points

Bill,

Thanks!

Regarding the PTV15 resistor, I will assume that the 45.3 ohm resistor is required with approx 0.03W or lower power rating. Let me know if you agree or know otherwise.

Bill

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C6678 Unused DDR3 Configuration