CC2540: CC2540 32K crystal oscillator frequency test

Hank Zhang

Expert 2040 points

Part Number: CC2540
Other Parts Discussed in Thread: CC2640

Whether the 32K crystal oscillator of CC2540 can be measured through GPIO port, just as CC2640 can output the actual frequency through IO port.

How to optimize the ppm for 32K crystals

over 4 years ago

0 TER over 4 years ago

TI__Guru**** 317180 points

The frequency tolerance is given by the xtal so if you need a smaller ppm number you have to find a xtal with smaller tolerance.

The center frequency will also be dependent on the load caps to the xtal. If the center frequency is off always in one direction it's possible to adjust the load cap slightly to tune the center frequency.

0 Hank Zhang over 4 years ago in reply to TER

Expert 2040 points

“If the center frequency is off always in one direction it's possible to adjust the load cap slightly to tune the center frequency"

How should "the center frequency" be tested

0 TER over 4 years ago in reply to Hank Zhang

TI__Guru**** 317180 points

As you wrote you can get the 32 kHz signal out on a pin. The method will depend a bit with regards to which instrument you have in hand but you have to measure the frequency of this signal and get it to be as close to the wanted frequency as possible.

0 Hank Zhang over 4 years ago in reply to TER

Expert 2040 points

That's the problem, which pin.Can GPIO output this 32K frequency？I have a frequency meter

0 TER over 4 years ago in reply to Hank Zhang

TI__Guru**** 317180 points

See https://e2e.ti.com/support/wireless-connectivity/other-wireless/f/667/t/480157?How-to-output-cc2540-32k-crystal-signal-to-an-pin-for-measurement-

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CC2540: CC2540 32K crystal oscillator frequency test