LP-EM-CC2340R5: CC2340R5 32.768 Khz crystal PPM?

Markel Robregado

Part Number: LP-EM-CC2340R5
Other Parts Discussed in Thread: CC2340R5, CC2640R2F

Tool/software:

Hi,

The 32.768Khz crystal used at the CC2340R5 Launchpad is "CRYSTAL, RESONATOR, 32.768KHz, -380PPM/+380PPM, -40DEGC/+125DEGC, SMD - TAI-SAW". PPM is how much the crystal frequency deviates from original value. Is this -380 PPM/+380 PPM required for CC2340R5? Can we choose a 32.768 KHz crystal with lower PPM?

-kel

1 month ago

+1 Jake Pulliam 1 month ago

TI__Expert 6520 points

Hi Kel,

Yes it's no problem to use a crystal with a lower PPM (higher accuracy).

-Jake

0 Markel Robregado 1 month ago in reply to Jake Pulliam

Guru 86235 points

Hi,

Your design files BOM regarding the 32.768 Khz crystal maybe not correct. I browsed the Tai-Saw website there is no 32.768 Khz crystal with -380 PPM/380 PPM.

I assume the 32.768 Khz crystal required for CC2340R5 needs 3.3V input?

-kel

0 Markel Robregado 1 month ago in reply to Markel Robregado

Guru 86235 points

When I worked with CC2640R2F custom board before we choose the same crystal as the launchpad. My concern with CC2340R5 is that if we choose an alternate manufacturer crystal that it might have problems. There has been issues of crystal not starting.

-kel

0 Markel Robregado 1 month ago in reply to Markel Robregado

Guru 86235 points

Hi,

The load capacitors at 32.768 Khz are different 12pF and 15pF. Is that correct? Should it be the same value?

-kel

+1 Jake Pulliam 1 month ago in reply to Markel Robregado

TI__Expert 6520 points

Hi Kel,

To address your questions in order:

1) The crystal part number is correct, if you have questions regarding procuring the device please reach out to Tai-Saw directly

2) The 32kHz crystal oscillator is functional across the supported operating condition of the CC2340

3) We have an application note that describes a number of alternate parts that have been tested by TI or the crystal manufacturers. See https://www.ti.com/lit/an/swra495k/swra495k.pdf

4) Yes the design is correct with the different components. If you choose a crystal with a different load capacitance then you would need to adjust this to match the target load capacitance.

BR,

Jake

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LP-EM-CC2340R5: CC2340R5 32.768 Khz crystal PPM?