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MSP430F5438A - Running ADC at 1.8V?

Jonathan Tate
Intellectual 1745 points
Other Parts Discussed in Thread: MSP430F5438A

MSP430F5438A.  

My customer has a few peripherals that have to run at 1.8V.

 

Page 39 of the MSP430’s datasheet calls out an operating range of 1.8V-3.6V and that the analog supply input has to be within 0.3V volts of that. However, page 62 of that datasheet states that for ‘full performance,’ the ADC needs to be run from 2.2-3.6V.

 

It would be very convenient if they could run everything at 1.8V.

 

Do you know what problems they might run into if they run the entire MSP430, including the analog supply and ADCs, at 1.8V?

Thanks

  • 0
    Expert 2080 points

    The internal reference is running in "reduced performance" with 1,8V supply too, which means reduced accuracy, perhaps longer turn-on time. I believe that the problem with the ADC in "not full performance" are the error parameters, running ADC at low power supply will not satisfy the parameters in the datasheet, ie lower frequency, lower accuracy, longer sampling time, etc...

    Perhaps the internal ADC12OSC will simply not run (try setting the DCO to 25Mhz with 1,8V).

    But I have no idea how big will the difference be.

  • 0
    Expert 1790 points

    Hi Jonathan,

    I've asked the question a TI application engineer on an exhibition. He said:

    "1. There is no official answer for using an ADC below 2.2V.

    2. There is a high likelyhood that is works but the results are outside of specified tollerance."

    I recommend to use a small DC/DC converter and get the voltage up to 3.3V. You will save a lot of hasle. TI offers DC/DC converter applications where you can switch on the converter by the MCU, when needed.

    Regards

    Guenther

  • 0
    Guru 227245 points

    Jonathan Tate said:
    Do you know what problems they might run into if they run the entire MSP430, including the analog supply and ADCs, at 1.8V

    The internal reference won't work. It requires AVcc to be at least 2.2V for the internal 1.5V reference and 2.8V for the 2.5V reference. Below 2.2V, the reference is unstable and won't be able to drive the rewuired current for the conversions.
    It should be possible to run the ADC with an external 1.4V reference, the there is a margin of 0.4V between reference and ADC12 logic, which sould be good enough to let it work properly (remember, only 2.8V are necessary for the 2.5V reference).
    Chances are, that the given toleracnes cannot be met if the ADC12 is run at such a low voltage.

    Alternatively, a simple and cheap charge pump will double the 1.8V to 3.6V and allow full performance, including analog sampling of values up to the 1.8V (actually up to 2.5V) which wouldn't be possible with a 1.5V reference.

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