MSP430FR5969-SP: Clock Source and Compatibility Inquiry

Part Number: MSP430FR5969-SP
Other Parts Discussed in Thread: MSP430FR5959

Tool/software:

Hello,

I wanted to ask about the MSP430FR5969-SP regarding time counting. Would it be better to use the internal clock, or would adding an external radiation-tolerant 32.768 kHz oscillator (Q-Tech QT178L10B-32.768KHz, 100ppm) be a more suitable option?

Could you provide feedback on which approach would be more beneficial in terms of clock deviation?

Additionally, I have another question regarding external oscillator compatibility. If the external oscillator were to be connected to pin 45 (LFXIN), would it be compatible with the Q-Tech oscillator mentioned above? The datasheet states:

PJ.4/LFXIN (Pin 45) – General-purpose digital I/O, Input for low-frequency crystal oscillator LFXT (In RHA and DA packages: MSP430FR594x devices only)


I would greatly appreciate any information you can provide on this matter.

Best regards,

Aitor

  • Without knowing your accuracy requirements, it is hard to give an answer.

  • From your question, I'm not sure I understand the alternative you're proposing. Would your alternative be to connect a crystal to the MSP's internal oscillator? If so, then the accuracy of that alternative would be almost entirely dependent on the crystal that you chose. And depending on the quality of the crystal, that might be a more- or less-expensive alternative than using the packaged external oscillator.

    Also, is radiation hardening an actual concern in your application or is it just a positive attribute of your proposed external oscillator?

    Also, does you design have just one consumer of this 32 kHz source or could that one external oscillator feed multiple microprocessors/FPGAs/etc.? In that case, the single external oscillator might be a good choice (or you could probably condition your MSP430 to deliver ACLK on an output pin and feed that onwards to the additional consumers).

    Finally, some engineers are just more comfortable specifying an external oscillator than specifying a crystal and the necessary loading capacitors.

  • Hello,

    Let me clarify my question.

    I want to connect an external oscillator to the MSP430FR5969-SP to provide an external clock input instead of using the internal one.

    I initially thought that pin 45 (LFXIN) could accept a TTL clock signal and use it internally, rather than using a crystal connected between LFXIN and LFXOUT. However, I need confirmation on whether LFXIN can directly accept a TTL oscillator clock input.

    I understand that an external crystal can be placed between LFXIN and LFXOUT, but in my case, I am only allowed to use an oscillator with a TTL output.

    Could you confirm if this setup is possible? Would the Q-Tech QT178L10B-32.768KHz (100ppm) oscillator be compatible with this configuration?

    I appreciate your help.

    Best regards,

    Aitor

  • I can't speak specifically about the MSP430FR5959 (because I haven't looked at its Data Sheet) but certainly most MSP430 chips have a way to configure each of their internal crystal oscillators to instead accept an external CMOS (~TTL) level input from an external oscillator. In my product, we use our MSP430F5359s in exactly that way, driving two MSPs and one Nordic Radio chip from a single common 32 kHz external crystal oscillator.

    (It would be almost impossible to design an on-chip crystal oscillator in such a way that it COULDN'T be driven by an external clock signal on its input pin.)

    Here's the relevant table from the 5xx/6xx Family User's Guide:

  • Thanks, indead I have finally found in the datasheet that a external square-wave input frequency can be fed to the pin45.

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