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MSP430G2755: Voltage Supply Ripple Tolerance

Part Number: MSP430G2755

Hi,

I have a voltage regulator that will likely have a few 100mV of voltage ripple that will be feeding the MSP430G2755.  Is there any concern on normally operation of the MSP430 with this much ripple?

Regards,

Jake

  • Hi Jake,

    This should be fine but what is the VCC level and can this ripple occur during ramp-up? Pages 25/26 of the User's Guide (POR and BOR specifications) cover everything you need to know about this topic.

    Regards,
    Ryan
  • It is normal practice to eliminate such ripple with LC, RC filter or using LDO or/and adding additional capacity decoupling buffer. What can affect with this ripple? Probably any analog functionality including ADC, DAC, Capacitive Sensing, buttons/switchers debouncing filters, comparators and so on...

    Regards,

    Alexey

  • PS: And of course, gate logic switching time lag. So, if voltage ripple is 1-4 MHz - this is one case, if voltage ripple 50-200kHz - the other.
  • Thanks Alexey and Ryan,

    The ripple should be relatively slow ~120Hz. Ripple should be between 2.2V and 3V.

    I was not aware of the time lag in the switching logic. Can you expand on this?

    Regards,
    Jake
  • Jacob,

    Every MSP430 MCU has internal LDO for Core logic (usually it is an internal 1.2V low-side bus) . So, CPU, memory and so on is protected from such ripple by default. But high-side bus peripherals are not. The latest generation of MSP devices like FR59XX has quite fast peripheral gate logic time lag for semiconductor elements, but for older models like FR69XX or even FR41XX it has 4 times longer switching time. In such transitions the ripple can 'hit' many times gate threshold voltage or can significantly decrease noise immunity for external digital communications. That is, every 'digital' signal differs from pure sine-wave only by spectrum, the first one has fundamental sine wave frequency and its infinite (in theory, practically limited by inductance, resistance and capacitance of trace paths) number of sine-wave harmonics, but in the second one has only one sine wave, theoretically goes in spectrum to only fundamental frequency.

    Regards,
    Alexey

  • PS: but since the MSP430 is actually low power device, it is easy to filter 120Hz ripple with RC low-pass filter with 50 Ohm resistor with 100 uF low-voltage capacitor. Current flow will be limited in MCU to 20mA, but this is also a good practice to protect MCU from malfunction in such cases as reverse polarity.

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