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In this device, I'm using this 26MHz crystal.

The datasheet only specifies the minimum crystal drive level as 500 μW.

enter image description here

The above shown crystal has a maximum drive level of 300 μW.

  1. I understand that the crystal drive level is the maximum power dissipated in the crystal. So, the datasheet of the USB device should give the maximum value of the crystal drive level, right? Why is only a minimum value given?

  2. I guess that since the drive level of the selected crystal is lower than the USB datasheet, I should not use it. Can someone tell me the reason why it should not be used? For this, I did some reading on the accepted answer to this question. It was not very clear. Can someone clarify in simple terms?

ocrdu
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2 Answers2

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the datasheet of the USB device should give the maximum value of the crystal drive level, right?

It does. The 500μW specification is the minimum requirement on the crystal. After all, the whole table is called Quartz Crystal Specifications. It implies that the USB chip is guaranteed not to drive more than 500μW into the crystal under worst case conditions across temperature and supply voltage.

As long as a crystal can accept drive levels up to 500μW, the USB chip is guaranteed not to overdrive the crystal.

A 300μW maximum drive level crystal doesn't meet the specification, since it needs to at least handle a 500μW drive level per the table you've quoted.

Kuba hasn't forgotten Monica
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The crystal needs to handle being connected to the chip and crystals have a maximum power limit they can handle without damage.

The chip will drive the crystal at some power and requires a crystal that can handle at least the given amount or more.

Crystals may damage if driven with too much power.

Justme
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  • Thank you for your answer. So, I need a crystal with a higher drive level and less ESR than the selected crystal part, right? –  Apr 03 '23 at 05:51
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    Yes. Usually that means a bigger packages since package size determines some of the important crystal parameters. – Turbo J Apr 03 '23 at 07:22