AM3352: Static VTP concerns

Nick, please provide the following:

- DDR type
- Frequency of DDR operation
- temperature range expected of DRAM/AM335x

Regards, Siva

- DDR3L SDRAM

- 400MHz

- generally ambient will be in 25C-35C, but there will be frequent cases that range from -40C to 95C 

thanks!

Is 95C the Junction temperature or case temperature of the processor? Are you adjusting the refresh rate for the DRAM for higher temperatures?

Regards, Siva

95C will be the ambient environment temp in certain use cases. 

We are using the default configuration for SDRAM of the beagle bone black

George

Thanks for providing the details. All the data we have on our DDR3 interface running at the max. frequency of 400MHz clock rate is with VTP enabled for dynamic compensation.

- In you set the filter setting bits 3-1 of the vtp_ctrl register to 111 instead of 011 you might be using currently? Does this setting help with the EMI performance in your system?
- What are the SDRAM drive and termination settings (ODT for SRAM and AM335x) you are using? Do any of the drive/termination settings make a difference in the results?

We have some options to address the situation here, in case the filter options are not helping you to reduce the EMI concerns:

- Use Static VTP (one time compensation for process) and de-rate the frequency so the interface can work robustly across the entire temperature range. Change the frequency to 366MHz instead of 400MHz to give good guard band

- Use SW assisted Dynamic VTP i.e. detect temperature change and enable VTP as you see change in temperature say every 5C. This could be tricky and possibly add complexity to the system

Regards, Siva

George

Another important note: You mentioned the case temperature can go as high as 95C - this will require the SDRAM to double refresh rate. Typically, SDRAM's have standard refresh rate for Tc <85C and require 2x refresh rate for Tc>85C.

Please make sure you adjust your SDRAM timing parameters accordingly

Regards, Siva