AM335x X'tal specification

Ichiro Fukui

Hi,

Our customer has a question about x'tal for AM335x series. How can we consider the required specification of crystal?

On AM335x spec, it is clearly mentioned that it must be within +/- 50ppm. Initial accuracy, temperature drift, and aging effects should be combined when evaluating a reference clock for this requirement

The other hand, it seems that the x'tal on our EVM does NOT meet this specification.

- Abracon : ABM3-25.000MHz http://www.mouser.com/ds/2/3/abm3-47699.pdf

- Suntsu : SCC18B-24.000MHz http://www.suntsuinc.com/pdfs/quartz-crystals/suntsu-sccseries.pdf

AM335x SKE:

- Citizen : CS325-24.000MABJ-UT (+/- 30ppm) http://cfm.citizen.co.jp/english/product/pdf/CS325.pdf

beagleboneblack:

- TXC : 7A-24.000MAAJ-T (+/- 30ppm) http://www.txc.com.tw/download/products/xtal/7A_c.pdf http://www.mouser.com/ds/2/96/008-0360-0-11484.pdf

Even +/- 30ppm type of crystal, it can not meet our spec when we consider following parameter, when we add (combine) below.

1. Initial accuracy

2. Temperature drift

3. Aging effects

How do we consider x'tal spec? Do we need add above 3 parameter? Or it is ok if each 3 parameters are within +/-50 ppm?

Regards,
Fukui

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi Fukui-san,

The specification is correct. All three parameters combined should be within or close enough to specified range. Also please note that the EVMs are not an end product, they are provided as a means of device evaluation.

0 Wolfgang Muees1 over 10 years ago

Genius 3685 points

For internal working of the CPU, no special accuracy is needed.

You only need accuracy for I/O: Ethernet, USB, etc.

Look into the specifications for I/O standards and derive your needed accuracy.

0 Ichiro Fukui over 10 years ago in reply to Biser Gatchev-XID

TI__Intellectual 1310 points

Hi Biser-san,

Thank you for your prompt reply.

> All three parameters combined should be within or close enough to specified range.

Let me confirm. To consider the requiremnt of 50 ppm for crystal, which one is correct?
(a) ( initial accracy + Temperature drift + Aging effect ) < 50 ppm
(b) initial accuracy < 50 ppm & Temperature drift < 50 ppm & Aging effect < 50 ppm

I also understand that this requirement is coming from serial interface specification, no impact for processor opperation.

Thanks in advance.

regards,
Fukui

0 Biser Gatchev-XID over 10 years ago in reply to Ichiro Fukui

TI__Guru**** 393215 points

Hi Fukui-san,

(a) is the correct one.

0 Wolfgang Muees1 over 10 years ago in reply to Ichiro Fukui

Genius 3685 points

If your "serial interface" is a V24/RS232, the working range of frequency is about +/- 2%. This will give you 20% bit shift per byte, and this is OK. So don't worry about 50ppm.

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AM335x X'tal specification