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Original question:

MSP430FR2355: MSP430FR2355 JTAG CONNECT FAILURE - MSP - FET430UIF POWER OFF ISSUE

MSP430FR2355: MSP430FR2355 Analog SAC Noise Figure Question

Aosker Liu
Prodigy 520 points
Part Number: MSP430FR2355


Hi team 

Good day.

My customer want to know that:

The datasheet for MSP430FR2355TRSMR is very sparse on the details of the SAC analog opamps.

1. The Eni noise spec seems very off. 40uV in the range 0.1 - 10Hz.
However, the noise density spec is 64 and 28nV/sqrt(Hz).

I cannot believe that the device is a few orders of magnitude noisy between 0.1 to 10Hz. Noise density does go up, but is it indeed that high?

2. Is there a graph of the noise density (nV/sqrt(Hz) over frequency that you can provide?

3. What are the values of the feedback and input resistance when I select the internal resistive taps to set the gain of the opamp. The datasheet says I can set gain from 1x to 32x, but without knowing the resistance of the resistors, I have no idea what the NF of the opamp is. Also I cannot compute how much the opamp will load the circuit/sensor which is feeding the opamp.

Best regards
Aosker

  • 0
    TI__Prodigy 520 points

    and another is :

    MSP430FR2355: MSP430FR2355 Smart Analog Combo

    The Family User Guide says the following:
    Table 20-6. SACxOA Register Description
    SACEN SAC enable. This bit enables or disables the SAC.
    OAEN SAC OA enable. This bit enables or disables the SAC.
    0b = SAC OA is disabled, then the SAC OA output high impedance


    1. What I want to do is enable SAC1 with SAC1OA SACEN=enable, and have its opamp output go to eCOMP1 comparator. But at the same time, I want to set SAC1)A OAEN=0, so that the opamp output does not appear on the output pin P1.5/OA1O/A5.

    2. While I am using the opamp SAC1 to drive eCOMP1, can I simultaneously drive pin P1.5/OA1O/A5 with an extrernal analog voltage (because I did not enable the OAEN bit above), and thus be able to send A5 to the ADC?

    The above is my main question.
    Also some additional questions .. but please do answer my above question.

    3. Can I at sometime, disable the ADC and use the same pin P1.5/OA1O/A5 as a digital output pin and drive it as a GOIO?

    4. When I am disabling the ADC, can I first drive the pin as a GPIO low (or high) and then after that disable the ADC. I need to sequence it this was to make sure the pin does not float during the transition. (The external circuit driving the analog pin P1.5/OA1O/A5 has a resistance, so contention is not an issue).

    Thanks

  • 0 in reply to Aosker Liu
    TI__Intellectual 2585 points

    Hi,

    For 1 and 2, 

    Please refer to the SAC connection block

    If you don't want to OA output to IO port, directly change the IO mux as below: It will also disconnect the ADC for OA. 

    Also, You can use the ecomp and OA output and ADC input at the same time. 

    Q3, same as above. 

    Q4, You can direct change the IO mux with setting PxOUT = 0 firstly, then change the PxSEL to GPIO. It will no float situation. 

  • 0
    Prodigy 10 points

    Thanks. I see the page with the IO port pin IOMux.
    That answers my question 1.

    My question #2 -- I guess the answer would be "No?"
    2. While I am using the opamp SAC1 to drive eCOMP1, can I simultaneously drive pin P1.5/OA1O/A5 with an extrernal analog voltage (because I did not enable the OAEN bit above), and thus be able to send A5 to the ADC?

    Because the IOMUX has one setting to enable both the SAC out to the pin and the ADC input, so either I get both SAC out and ADC in on that pin. Or I get neither of them.

    Is that correct?

  • 0 in reply to Shrikumar KA6Q
    TI__Intellectual 2585 points

    The answer is yes. From the block, you can find 2 muxs. after the OA output, it go to IO mux and eComp mux. From IO mux, you can choose to connect to OAO or A5. The OAEN is the OA enable/disable control. You may misunderstand the bit. If you disable, you will disable the OA itself. 

  • 0 in reply to Hawken Li
    TI__Genius 9880 points

    Hi Hawken Li,

    Im replying you on this case in behalf of customer Shrikumar for, he is having a trouble with the TI account. Below is the follow up question.

    "
    I would like to send SAC1 to COMP1. At the same time I want to send pin P1.5 to ADC A5. Different signals and they should not short. What registers settings will do that?

    "

    Regards,

    Maynard

  • 0 in reply to May
    TI__Intellectual 2585 points

    Hi, Maynard, 

    I guess you want to enable the ADC read the OA output and also want to use the eComp to do the real time comparator. It is very easy. Please use the IO MUX set to P1SEL = 0x11, and eCOMP input MUX set to OA. You will get the result. 

  • 0 in reply to Hawken Li
    TI__Mastermind 30510 points

    Hi Hawken,

    For some technical reason our customer can't reply to this thread so I'm posting his response in his behalf. Here are the customer's inquiries.

    What registers do I set to make this possible?
    Is this possible ? Or not possible?

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Intellectual 2585 points

    Hi, Danilo

    It cannot be achieved. The internal connection is fixed. If you want to use OA0 function, the P1.1 cannot be used as external ADC input at the same time. Only solution is to disable OA and read the external ADC and then enable OA. But at the same time the eCOMP should be stopped also. 

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