MSP430AFE253: MSP430AFE253 32KHz crystal source

Dario Rastelli

Prodigy 30 points

Part Number: MSP430AFE253
Other Parts Discussed in Thread: MSP430F6733

Hello!

Looking at the MSP430AFE253 datasheet it seems that there is no possible to use the LFXT1 source with 32KHz Crystal.

Is is true?

Which is the more power saving way to have a 1 sec timing to get data from the SD24?

I tried the VLO, but it is very unstable: far away from a good time clock.

Could you please suggest me something?

Thanks in advance

Dario Rastelli

over 8 years ago

0 Clemens Ladisch over 8 years ago

Guru 318760 points

The AFE253 indeed does not have an LFXT1.

To get precise timing, use a crystal with at least 400 kHz (for XT2), or use an external timer chip, or replace the AFE253 with some other model.

Is it really necessary to have accurate sample timing? How much accuracy is needed?

0 Dario Rastelli over 8 years ago in reply to Clemens Ladisch

Prodigy 30 points

Thanks for the reply.

I need to save samples at a certain time, according to a specific period in seconds (it has to be done for long time, so it has to be accurate to avoid drift...)

Using XT2 of 400kHz could be an option, but increasing power consumption.

I am also evaluating other options (with at least 3 SigmaDelta ADC), as MSP430F6733: I saw that this supports the 32KHz crystal with an internal RTC.

Could you give me a feedback on this possible choice? Any better alternative?

Thanks in advance

0 Clemens Ladisch over 8 years ago in reply to Dario Rastelli

Guru 318760 points

How much accruracy is needed?

0 Dario Rastelli over 8 years ago in reply to Clemens Ladisch

Prodigy 30 points

Consider that I want to keep aligned a date for at least 1 year wit a possible tolerance of 30 mins.

So 1 year = 12*30*24*3600 = 31.1Msec

accuracy could be < 1800/31M = about 50ppm

is it correct?

I didn't find the accuracy of RTC with a rapid check on the datasheet.

0 Clemens Ladisch over 8 years ago in reply to Dario Rastelli

Guru 318760 points

The RTC counts up whenever it gets a clock cycle from the crystal.

Crystals typically are 50 ppm or better.

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MSP430AFE253: MSP430AFE253 32KHz crystal source