Why DM8168 can't run in DDRIII ar 1600MHZ?

SuitJune Young

Genius 3985 points

I designed a custom board using X8168 rev B,DDRIII using Hynix chips 1600M max.

Dm8168 can run in DDRIII at 1333MHz,but can't run in DDRIII at 1600MHz.

What's the possible causes?

First,PCB layout.

Second,I uses 51R+-5% resistor connected to 8168's VTP[x]_VTP pins.Could this be the cause?

And other causes?

Thank you in advance.

0 Biser Gatchev-XID over 12 years ago

There are limitations on the EMIF inside the DM816X. Maximum possible frequency is 796MHz or 1592M transactions per second.

For the resistor connected to the VTP pins 49.9Ohm 1% should be used, because this is the reference against which all DDR impedances are measured.

For board design see DM816X Datasheet, Section 8.3.2.

0 SuitJune Young over 12 years ago in reply to Biser Gatchev-XID

Genius 3985 points

Thank you~XID~

Still a quesion.If after 8168 resets,the avs core voltage is 0.89V,could this "low" volatege causes DM8168 CAN'T run in DDRIII at 1333MHz?

In other words,If I want to run in DDRIII at 1333MHz,the avs voltage HAVE TO be 1.0V?

0 Biser Gatchev-XID over 12 years ago in reply to SuitJune Young

0 SuitJune Young over 12 years ago in reply to Biser Gatchev-XID

Genius 3985 points

yes,we followed that tutorial,but the problem doesn't disappear.

Right Now,I have another question:When DM8168 after resets,the Core AVS volatege have to be 1.0V?Can the CVDD core AVS voltage be 0.9V after Reset?

Our test shows that when DM8168 is powered 0.9V after resets,the DDRIII can't run.

And when DM8618 is powered at 1.0V,the DDRIII can run at 1333MHz.

0 Biser Gatchev-XID over 12 years ago in reply to SuitJune Young

On the EVM the Core AVS voltage is set to be 1.0V at start-up time, before processor assumes control.

0 SuitJune Young over 12 years ago in reply to Biser Gatchev-XID

Genius 3985 points

..........................you don't answer my questions yet.

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