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C5505A ADC questions: offset and GAIN0 divider accuracy

Neil Shrowder
Prodigy 10 points

I have three questions regarding the ADC in the TMS320C5505A. I have read the relevant parts of SPRS660F (Sept 2013) and SPRUFP1C (Jan 2012).

My application:  measuring external battery voltage using channel 1, and other internal signals using channels 3,4 and 5.

Question 1: Regarding the offset on each ADC channel:

The data sheet specifies a maximum offset of 2 LSB for the ADC.

Is the offset the same on all channels ?

In other words, when we measure the offset using channel 0 (according to the procedure in section 2.4 of SPRUFP1C), can we subtract this offset from all the ADC channels, to improve their accuracy ?

Question 2: referring to figure 2 in SPRUFP1C : what is the tolerance of the division ratio of the channel 1 voltage divider (nominally 1/8) ? (I cannot find this in the data sheet.)

Question 3: referring to figure 2 in SPRUFP1C : what is the tolerance of the impedance to ground at GPAIN0 when GNDON is on (nominally 280k + 40k)? (I cannot find this in the data sheet.)


Thanks,

Neil.

  • 0
    TI__Genius 12575 points

    Hi,

    With respect to your application - measuring external battery voltage using channel 1, and other internal signals using channels 3,4 and 5. - This Looks ok.

    Also, below are the my replies for your Qs.

    A1. Yes when you caliberate and there exists an offset then this needs to be applied (difference) to the battery reading, that can be obtained by switching to channel 1 and sampling the battery voltage through the voltage divider.

    A2. Yes, The voltage divider divides the value from channel 1 by a factor of 8. With respect to the limits mentioned in datasheet - I need to further check.

    A3. Again I might need to further check (beyond datasheet) and will get back .

    Regards

     Vasanth