Wio E5 LSE Drive Strength

Products & Technology LoRa
#1

From looking at the BOM for the E5 module, many alternate crystals are listed. One of these, Epson FC-135-32.768k-12.5 is listed. This particular oscillator is called out in Table 7 of ST app note AN2867 (Oscillator design guide for …).

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Specifically, the gmcrit for this crystal is 2.1312 uA/V. In table 5 of AN2867, the gm of the oscillator and the associated gmcrit is listed in the table. For this crystal, it seems that high drive is required to get the gm_crit_max to be over the gmcrit of the crystal.

The problem is that the sample code uses low drive. This makes the gain margin less than 1 when the app note wants the gain margin > 5.

Is this correct, or am I missing something?

#2

Does anyone from Seeed even read this forum? Getting the drive strength for the LSE is critical in using the device properly. Obviously, in the factory-shipped AT command code, the LSE is set up in some way. I would just like to know what it is.

#3

Please note that for oscillator starting, gm must satisfy gm>gmcrit.

#4

Can you confirm the gmcrit of the 32 kHz oscillator used in the Wio-E5 module? Is it 2.1312 uA/V or was a different oscillator selected?

Thanks