How to use the EMC_FBCK pin

[MarcoAEE]

Hello everybody,
I'm designing a new board based on LPC54618FBD208 with 2 SDRAM modules (16bit + 16bit data bus) and 1 parallel NOR Flash module (16bit data bus) managed by the EMC functional block of the MCU.
For the SDRAM I will use the Y-topology to have a 32bit data bus configuration but I don't quite understand how to use the EMC_FBCK pin.

Options:
1 - I have to connect it to the farthest point of the EMC_CLK0 signal (i.e. to the pin of one of the two SDRAMs, obviously the distance is the same for both since the distances must match)
2 - I have to connect it to the EMC_CLK0 pin with a track of length equal to the length of the signal of EMC_CLK0 between MCU and one of the two SDRAMs
3 - I have to connect it directly to the EMC_CLK0 pin regardless of its length

Thank you
Marco

[xiangjun_rong]

Hi,

I suggest you download the an12026.pdf, which focuses on the SDRAM hardware connection and layout.

https://www.nxp.com.cn/docs/en/nxp/application-notes/AN12026.pdf

The EMC_FBCK is  the Feedback clock to sample SDRAM data, it has two sources, one is internal connection to EMC_CLKOUT0 via a delay logic by gates, another is connected to EMC_FBCLK pad. Pls rtefer to section 2.2 EMC pins in an12026.pdf.

Hope it can help you

BR

XiangJun Rong

[MarcoAEE]

Hi,

thanks, I had already viewed the application note, I saw the following note in section 2.2:

EMC can use either EMC_FBCLK pin or EMC_CLK0 loopback signal as its feedback input;
for EMC_CLK0 loopback signal, programmable delays can be added to clock feedback path, to compensate signal flight time.

I don't understand at what point I have to acquire the EMC_CLK signal with EMC_FBCLK pin (i.e. at what point I have to join the two tracks)

Thank you

Marco

[xiangjun_rong · Accepted solution]

Hi,

I suggest you read the section 2.5.2 Function of EMC_CLKIN pin for an10935.pdf, which can be downloaded from the link:

https://www.nxp.com.cn/docs/en/application-note/AN10935.pdf

BR

XiangJun Rong

[MarcoAEE]

Hi,
thanks, it is all clear! Bearing in mind that with LPC54618 the EMC frequency will be 90Mhz and that my layout is very compact, I can connect EMC_FBCLK directly to the EMC_CLK pin.
Thank you
Best regards
Marco