i.mX1060 24MHz Crystal Requirements

[Gharb0129]

Hello,

We are using the i.MX1060 and had a few questions regarding the 24MHz crystal.

1. The data sheet specifies the maximum drive level at a typical ESR. The hardware design reference sheet lists two examples:

   • 250uW (max) @ 80ESR (typ)

   • 200uW (max) @ 50ESR (typ)

   • To avoid overdriving the crystal, can a lower drive level crystal (rated for say 100uW) be used natively with the IMX processor? Is the drive voltage fixed?

   • What is the maximum ESR that is acceptable? Crystal datasheets don't usually show the typical ESR. It's usually specified as "MAX".
2. What is the PPM requirement for this crystal? Is 30ppm acceptable? We are not using the USB interface but are using the Ethernet (RMII).

Thanks!

-Greg

[kerryzhou]

Hi @Gharb0129 

  Sorry for my later reply.

 Please check the following information:

>>1.customer need to use use low driver level crystal 100uW, to avoid overdriving the crystal, whether that be OK?  

As you mentioned, we've listed some typical crystal for customer reference.

About 100uW crystal,  customer need to calculate the DL to make sure it doesn't exceed DL limitation.

>>2. Is the drive voltage fixed? What is the maximum ESR that is acceptable? 

For the drive voltage, the MAX reference voltage is NVCC_PLL  in RT1060.

RT10**: ESR<80, CL<12pF (notice: gm is just simulation results)

>>So, could you please recommend another crystal? customer needs to use 30ppm.

partnumber:  XRCGB24M000F2P91R0 FYI.

Wish it helps you!

Best Regards,

Kerry

[Gharb0129]

Hi Kerry,

Thank you for the responses. Two more questions that will help us with our verification:

1. What is the pin capacitance of XTALI and XTALO for the i.MX processor? This is usually in the datasheet of the processor and is used to calculate the load capacitors of the 24MHz crystal.
2. What is the oscillator transconductance? 

Regards,

-Greg

[kerryzhou]

Hi @Gharb0129 

1. What is the pin capacitance of XTALI and XTALO for the i.MX processor? This is usually in the datasheet of the processor and is used to calculate the load capacitors of the 24MHz crystal.

Answer: you can consider it as Co= 2pf.

2 What is the oscillator transconductance? 

Answer: Gm_min of internal OSC circuit (A/V) is 7.6E-04.

Wish it helps you!

Kerry

[kerryzhou]

Hi @Gharb0129 ,

   Thanks for your interest in the NXP MIMXRT product, I would like to provide service for you.

Answer your questions:

We are using the i.MX1060 and had a few questions regarding the 24MHz crystal.

1. The data sheet specifies the maximum drive level at a typical ESR. The hardware design reference sheet lists two examples:

   • 250uW (max) @ 80ESR (typ)

   • 200uW (max) @ 50ESR (typ)

   • To avoid overdriving the crystal, can a lower drive level crystal (rated for say 100uW) be used natively with the IMX processor? Is the drive voltage fixed?

   • What is the maximum ESR that is acceptable? Crystal datasheets don't usually show the typical ESR. It's usually specified as "MAX".

Answer: To get better performance, it's better to refer to the hardware guide, select 250uW,80ESR. 200uW, 50ESR. About the 100uW, if you have hardware, you can replace it to check, wehther the crystal can be oscillating or not. The driver voltage is not  fixed, if it can oscillating, I think it is OK to work. About the ESR maximum, it is not determined, we suggest you choose the hardware guide recommend value, as that is tested and works OK.

2 What is the PPM requirement for this crystal? Is 30ppm acceptable? We are not using the USB interface but are using the Ethernet (RMII).

Answer" You can choose 30ppm, it's OK.

Best Regards,

Kerry

[Gharb0129]

Hi Kerry,

Thank you for the response.

The drive level still concerns me. We want to use a crystal with a drivel level of a 100uW and testing it will not prove whether it works or not. Exceeding the drive level of a crystal will not cause an immediate failure but will cause it to fail long term. Below is a snippet from a white paper which explains what happens when you exceed the drive level. We could put a resistor in series with our crystal to lower the voltage across it. Lowering the voltage across the crystal will prevent us from exceeding the drive level.

Are you certain that the drive voltage is not fixed? If we know the drive voltage then we can determine how large of a resistor we need to put in series with our crystal. We measured the voltage across the crystal with an o-scope on the i.MX eval board and found it to be about 600mV.

Also, could you share the part number of the 24MHz oscillator (Y1) that was used on the eval board (

MIMXRT1060-EVK)?  The part # is not on the BOM in the eval board documentation.

-Greg

[kerryzhou]

Hi @Gharb0129 ,

   Please keep patient, I will help you to check with our internal hardware expert, then will give you a reply!

   Any updated information will let you know.

Best Regards,

Kerry