MSP430FR2355: XF1 Crystal requirements

Hi Tashira-san

Q1) HFXT frequency max value is tested using the accurate 24MHz clock source. So, the frequency deviation is not included. but considering the crystal error is inside several hundred PPM on the whole temperature, I think user can use the fundamental crystal based on the enough production test.

Q2) We haven't the test data based on 3rd overtone crystal. I think user can test if it can work by himself.

Thanks!

Hi Xiaodong,

Thanks for your reply and I am sorry for my late reply.
Regarding Q1), do you mean the maximum input requirement is strictly 24MHz?
If so, customers cannot use typ. 24MHz crystals because these crystals have frequency deviation in practice.
(there is no crystal generate exact 24MHz frequency)

Suppose customer wants to use below crystal with typ.24MHz, it is violating MSP430 specification?
https://www.ndk.com/en/products/search/crystal/1188120_1494.html
I am afraid it is not acceptable by customers.

Thanks and regards,
Koichiro Tashiro

Hi Tashira-san,

I understood the customer concern on the 24MHz crystal.

I think customer can consider using 8MHz crystal and FLL lock to achieve the 24MHz machine clock. Could you please help to check with customer if this solution can work?

Thanks!

Hi Xiaodong,

Could you clarify a bit more about the below usage?

Xiaodong LI said:

using 8MHz crystal and FLL lock to achieve the 24MHz machine clock.

According to User's guide Figure 3-1, I thought XT1 clock can be used as FLL reference clock.
In this case, DCO is used as clock source as described in Data sheet Table 5-5 and XT1 only supports 32kHz in this scenario.

Thanks and regards,
Koichiro Tashiro

Hi Tashira-san,

Thanks for your feedback! Sorry to my typo. yes, the solution is "the external 32768-Hz crystal can be used as the FLL reference" according to slau445i (FR2xx/4xx UG).

Thanks again!

Hi Tashira-san

besides “the external 32768-Hz crystal +FLL" solution,

I have checked with our system and design team, the crystal with typ.24MHz https://www.ndk.com/en/products/search/crystal/1188120_1494.html can be used on FR2355 XT1 input w/o violating.

It will take a while to determine for us to update the datasheet and get it published. So, updated DS will be later.

Thanks!

Hi Xiaodong,

Thanks for your reply and taking actions!
Now I understood that specific crystal is OK.

Xiaodong LI said:

It will take a while to determine for us to update the datasheet and get it published. So, updated DS will be later.

Do you mean you will update DS and add specific frequency tolerance range?
Just in case, suppose above crystal is EOL or hard to buy, can customer select other crystals with the same range of frequency tolerance?

Thanks and regards,
Koichiro Tashiro