topic Re: LPC55xx with external clock in LPC Microcontrollers

LPC55xx with external clock

otsl — Tue, 22 Dec 2020 21:28:28 GMT

The datasheet for the LPC55S6x states that an external clock can be used on the XTAL32M_P pin if the clock is a square wave from 0V to 850mV. Can someone elaborate on this? What is the tolerance of "0" and "850mV"? Is a DC offset acceptable as long as the amplitude is 850mVpp? Is 850mV the absolute maximum for the the pin?

Previous LPC parts allowed an external oscillator to be capacitor divided and driven into the XTALIN pin, but that process will not guarantee a 0-850mV signal from a 3.3V oscillator (there will be some DC offset). Without a little more information (or a recommended circuit) it is near impossible to design a robust system.

Re: LPC55xx with external clock

ZhangJennie — Fri, 25 Dec 2020 01:25:33 GMT

DC offset is not acceptable as long as the amplitude is 850mVpp.
850mV is the absolute maximum for the the pin.
this pin absolute input range is 0-850mV.

Have a nice day

Jun Zhang

Best Regards

Jun Zhang

Re: LPC55xx with external clock

otsl — Wed, 30 Dec 2020 11:57:40 GMT

Thank you Jun. Can you also provide the minimum amplitude that will reliably be detected?

Re: LPC55xx with external clock

ZhangJennie — Sat, 02 Jan 2021 08:21:35 GMT

We don't have this minimum amplitude data.

But based on practice, I suggest you make sure the amplitude over 100mV.

Have a nice day

Jun Zhang