AM571x GPMC max. load capacitance

Srinivas Jagarapu

Other Parts Discussed in Thread: AM5728, AM5716

Hello,

AM57xx datasheet GPMC section says "Total GPMC load on any signal at 3.3V must not exceed 10pF".

I think this max load capacitance cutoff is less? Is it the I/Os drive strength restricting this?

In our design one NAND Falsh and two FPGAs are on GPMC. Flash has max 10pF and each FPGA has 7pF , so total max 24pF load.

Is the GPMC works at any lower frequency on 3.3V?

Moving to 1.8V GPMC is difficult in our application.

Please provide a working solution for GPMC 3.3V.

Regards,

Srinivas J

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Hi,

Can you post which document you refer to, and where in the document is this statement found?

0 Srinivas Jagarapu over 9 years ago in reply to Biser Gatchev-XID

Intellectual 510 points

Hi Biser,

Here it is..page no 227, note 1.
www.ti.com/.../am5716.pdf

Regards,
Srinivas J

0 Srinivas Jagarapu over 9 years ago in reply to Srinivas Jagarapu

Intellectual 510 points

Here is little more information..
I couldn't able to find the same in AM572x datasheet.
Currently we are going with AM5728, but at production we will move to AM5716.

Regards,
Srinivas J

0 Biser Gatchev-XID over 9 years ago in reply to Srinivas Jagarapu

TI__Guru**** 393215 points

Is your device AM571x or AM572x?

0 Srinivas Jagarapu over 9 years ago in reply to Biser Gatchev-XID

Intellectual 510 points

Currently we are going with AM5728, but at production we will move to AM5716.

Regards,
Srinivas J

0 Biser Gatchev-XID over 9 years ago in reply to Srinivas Jagarapu

TI__Guru**** 393215 points

I'm asking, because I can see no such restriction in the current AM572x Datasheet. I will check what is the status for AM571x and come back here.

0 Srinivas Jagarapu over 9 years ago in reply to Biser Gatchev-XID

Intellectual 510 points

Thank you.

Regards,
Srinivas J

0 Rogerio Almeida over 9 years ago in reply to Srinivas Jagarapu

TI__Mastermind 26205 points

We are sampling now AM571x and production will be available by 4Q16

0 peaves over 9 years ago in reply to Rogerio Almeida

TI__Guru 62855 points

The 10pF load limitation for GPMC only applies to AM571x devices. This limitation does not apply to AM572x devices.

You have three choices, continue to use AM572x devices, reduce the IO supply voltage for GPMC to 1.8 volts, or reduce the load to less than 10pf.

Regards,
Paul

0 Srinivas Jagarapu over 9 years ago in reply to peaves

Intellectual 510 points

Hi All,

Thanks for the replies.

Why is the 10pF limitation only for AM571x devices? will it get fixed later in any revision of the chip?

For the prototyping we are going with AM5728, as AM5716 industrial grade is not available at the moment? AM572x is overkill for our application.

Regards,

Srinivas J

0 peaves over 9 years ago in reply to Srinivas Jagarapu

TI__Guru 62855 points

This limitation is related to a physical design difference that was not discovered until it was too late to change. Currently, there are no plans to fix this limitation.

Regards,
Paul

0 Srinivas Jagarapu over 9 years ago in reply to peaves

Intellectual 510 points

Hi Paul,

After a quick study on our design, it looks like moving GPMC to 1.8V is a better solution for us.
I am assuming there won't be any issues for GPMC (1.8V) to drive a load of 24pF (NAND Flash+ 2 FPGAs) for frequencies up-to 66 MHz.Please confirm the same.

Regards,
Srinivas J

0 Srinivas Jagarapu over 9 years ago in reply to Srinivas Jagarapu

Intellectual 510 points

Hi,

After reading the AM5716 datasheet again, I can see the 10pF limitation only under synchronous mode of operation. Does it mean there won't be any issues with asynchronous mode of operation?

Regards,
Srinivas J

0 peaves over 9 years ago in reply to Srinivas Jagarapu

TI__Guru 62855 points

24pf load operating at 1.8 volts will not be a problem.

Regards,
Paul

0 peaves over 9 years ago in reply to peaves

TI__Guru 62855 points

There appears to be a mistake in the data sheet where the limitation is only shown on Synchronous mode. I think this limitation applies to all modes of operation. I have reached out to the design team to get more information on the limitation and it may take a few days to get a better answer. For now, assume this limitation applies to all modes of operation.

Regards,
Paul

0 peaves over 9 years ago in reply to peaves

TI__Guru 62855 points

I confirmed the limitation applies to all modes of operation. Advisory i921 in the AM571x Silicon Errata addresses this limitation. Please read Advisory i921 for a complete description of the limitation.

Regards,
Paul

0 Srinivas Jagarapu over 9 years ago in reply to peaves

Intellectual 510 points

Thank you.

Regards,

Srinivas J

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AM571x GPMC max. load capacitance