MSP430FW427: the external LF crystal drive capability

Yue TANG

Part Number: MSP430FW427

Hi,

Customer checked with me the external LF crystal drive capability of MSP430FW427. so far, their LF crystal need 0.5uW drive level. do we have this data?

over 6 years ago

0 Ryan Brown1 over 6 years ago

TI__Guru**** 205697 points

Hi Yue,

The MSP430 has the ability to drive this LFXT but it may not be the most dependable solution available. More important factors are the crystal's ESR and tolerance, can you customer share more information about the exact crystal they intend to use? Please review the following for recommendations, considerations, and test procedures:

www.ti.com/.../slaa322d.pdf
www.ti.com/.../slaa367.pdf

Regards,
Ryan

0 Yue TANG over 6 years ago in reply to Ryan Brown1

TI__Expert 8525 points

attached is the crystal datasheet. the Cl is 9pf, but they choosed 10pf load capacitors. so far, the problem is that some of their products can't start up , need a tweezers to short the crystal pin to make it work. please kindly share your experience on this case. thanks.

Q13FC1350000300_FC-135 32.768KHz 9.0 +20.0-20.0.pdf

0 Ryan Brown1 over 6 years ago in reply to Yue TANG

TI__Guru**** 205697 points

As shown in Table 3 of SLAA322, an ESR of 70 kOhm and tolerance of 20 ppm has a generally lower Safety Factor of crystals evaluated. The load capacitance values are acceptable (C1, C2 = 2*CL – 2*Cstray, where Cstray is from 2 to 4 pF) but the LFXT should be as close to the MCU as possible, with the load capacitors on the other side. This suggestion is covered in Section 3 of SLAA322, the document also mentions in Section 5.4 that the MSP430FW427 device has a weaker drive capability which can lead to very long start-up times. XTS toggling is recommended to alleviate the issue and an example is provided in Figure 10.

Regards,
Ryan

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MSP430FW427: the external LF crystal drive capability