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C5500 SAR Converter (NoHV=1)

Stan Sidorov
Expert 1985 points

Hi there,

c5535, 

I need to get channel 2 worked as ch4-ch5 in ADC. I am not interested in battery measurement. So how can I set NoHV in 1 to measure ch2? I found previous post    saying that NoHV is an undocumented test feature to disable the high voltage protection circuit for the channels. Is the any chance to have an access to NoHV?

Cheers

  • 0
    TI__Genius 12575 points

    Hi,

    Yes, as mentioned in the other forum post (http://e2e.ti.com/support/dsp/c5000/f/109/t/1886700) The protection circuit is enabled by default for normal operation and there is no access mechanism to NoHV through any configuration etc..

    Hope this clarifies.

    Regards

     Vasanth

  • 0 in reply to Vasantha K
    Intellectual 510 points
    I think that NoHV corresponds to bit 2 on SARPINCTRL register.
    Setting it to 1, I was able to read a voltage on GPAIN0 on channel 2.
    Voltage on GPAIN0 must NOT exceed VDD_ANA (1.3V)
    Powering both ends of a potentiometer to GND and VDD_ANA respectively and connecting middle point wiper to GPAINx pins I was able to read values between 6 to 1004 for GPAIN1-3 (channels 3 to 5) but only from 6 to 724 on GPAIN0 (channel 2)
    Documentation says that "NMOS pass gates won’t pass signals with voltage greater than VDD_ANA – Vt"
    so that means that Vt = 0.36V = 1.3*(1004-724)/1004
  • 0 in reply to Diego de la Cruz
    TI__Genius 12575 points

    Hi,

    As mentioned in this forum the protection circuit is enabled by default for normal operation and that's the reason there is no access mechanism provided to NoHV (through any configuration). I do not think you need to configure bit 2 in SARPINCTRL register. What was your reading with out setting bit 2 in SARPINCTRL register ?

    Regards

     Vasanth

  • 0 in reply to Vasantha K
    Intellectual 510 points

    Channel 2 didn't work, I think I got zero data values, I will check again later.

    Datasheets says:
    "Either NoHV or GndSwOn must be 1 to measure channels 0 or 1.
    NoHV must be 1 to measure ch2.
    If these conditions are not met then the ADC will measure GND."

    Not sure if normal operation means battery voltage measurement, the goal here is to be able to measure a voltage on GPAIN0 between 0 and VDD_ANA using channel 2. If GNDON is set to 1, Channels 0 and 1 can be used for battery voltage measurement, GNDON is documented (SARPINCTRL bit 1) but NOHV is not. If NOHV is set by default to 0, which I think is the case , according to the datasheet, there is no way Channel 2 can be used and there is no way to use channels 0 and 1, unless GNDON is set to 1.

    And by the way, I think that the polarity of NoHV bit is opposite to the polarity of the NoHV signal connected to the AND gate input as shown in SAR converter users guide SPRUFP1C Figure 1 (functional diagram). I think that in this figure, voltage protection happens when NoHV AND gate input is set to 1, and setting it to 0 allows to use channel 2.

  • 0 in reply to Diego de la Cruz
    TI__Genius 12575 points

    Hi,

    Is there any reason why you haven't used other channels, using other GPAIN1-3 pins for VDD_ANA measurement ?

    Regards

     Vasanth

  • 0 in reply to Vasantha K
    Intellectual 510 points

    Yes, I am using the four GPAIN0-3 pins to read the output voltage of 4 potentiometers.
    I confirm that without setting bit 2 (NoHV) in SARPINCTRL register, when GPAIN0 is any voltage between 0 and VDD_ANA the value read on Channels 0-2 is a constant low value of 9.