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28035 Internal Bandgap and Input Signal Range

andrew barnett66202
Intellectual 270 points

I must be doing something wrong, but maybe someone can explain the following to me.  I'm currently using the external reference in a 28035 circuit, and I'm trying to switch to the internal bandgap reference.  It seems that a 3.3 Volt input with the external reference produces the correct result (somewhere below 4095 due to the conditioning circuitry), but will saturate at 4095 when I use the internal bandgap reference.  Any idea as to what's going on?  What should the control register settings be?

Thanks in advance for any assistance.

  • 0
    TI__Guru 60865 points

    Hi Andrew,

    You shouldn't have to change anything in the register settings other than selecting internal/external reference.

    There will be some error in each reference mode that will make the actual conversions different from the expected.  This may make the conversion results saturate for one reference mode while they don't for the other.  I think it would be good to try 3-4 different voltages spread throughout the input range to determine if the ADC results have some error (at which point you can compare this error to what we specify in the datasheet to see if the device is functioning within specification), or if the ADC is simply not functioning at all in internal reference mode.