RT1062DVL6 Rev A vs B silicon for the crystal oscillator

[pschreiber]

I have a customer with an issue of the 24MHz crystal not starting up on their board, moving from Rev A silicon (works) to Rev B (dead).

The board uses a standard 18pf CL but has 4.7pf loading caps. These are nowhere close to being correct (27pf - 30pf is proper) but after a quick check of NXP's own reference board IMXRT1050-EVKB shows the same: 18pf CL crystal using 2x 4.7pf loading caps (C39 and C40). Customer obviously copied the EVKB.

I tried the following on the Rev B silicon board (I do not have access to the customer's Rev A board at this time). The 2M2 bias resistor is installed on the customer's board.

Try #1 - crystal with CL of 10pf, using 2x 18pf loading caps
Try #2 - crystal with CL of 6pf, using 2x 10pf loading caps

Neither would oscillate. There was no errata I could find about what changed from Rev A to Rev B regarding this issue. 

In BOTH NXP's own board, and the Rev A customer's board, this 24MHz crystal is working on pure luck (ie power supply noise probably). Well, the luck has run out.

[pschreiber]

I will check the power-up sequence timing/levels.

Can you say why NXP's own reference design does not have the proper crystal/loading caps?

[Omar_Anguiano]

The EVKs can be used as reference when building your design. When using a crystal it is important to check that it complies with the specification of the HDG; the load capacitance values need to be chosen according to the crystal manufacturer´s specification.

The HDG suggestions assure that the device will comply with ratings specified in the documents, besides if your environment is noisy it is suggested to follow the HDG.
This application note will help you improve EMC in i.MXRT series: https://www.nxp.com/docs/en/application-note/AN13202.pdf

If you have more questions do not hesitate to ask me.
Best regards,
Omar

[Omar_Anguiano]

Hello
Hope you are well.

It is important to check that customer followed the suggestions from the Hardware Development Guide.
Connect a fundamental-mode crystal between XTALI and XTALO. An typical 80 ESR crystal rated for a maximum drive level of 250 μW is acceptable. Alternately, a typical 50 ESR crystal rated for a maximum drive level of 200 μW may be used. Bias XTALI with a 2.2-M resistor to GND. Mount the resistor close to the XTALI ball.

Also please check that the power-up sequence is correct based on the HDG.

If you have more questions do not hesitate to ask me.
Best regards,
Omar