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LAUNCHXL-F280049C: ADCC readings not correct compared to ADCA

Wallace Tran
Intellectual 1305 points
Part Number: LAUNCHXL-F280049C

I tried adding ADCC support to on the adc_ex2_soc_epwm.c I found in MotorControl SDK. I basically just added ADCC alongside ADCA throughout this example.

 I am using a DC power supply to input 0-3V into the ADC channels and here were the results.

I multiply the result out of the ADC Result Registers by float_t (66.32)/4096 since 66.32 is my application’s full scale voltage.

DC Input Value

ADCA

ADCC

0 V

0

0

1 V

~20

~40

2 V

~40

~60

3 V

~60

~60

In addition, on the 049 LP, I use the VREFHI pin to be my 1.65V. When I plug into my ADCA channel, I get ~2048 which looks fine. When I plug into ADCC channel, I get 4096.

 I did a register by register comparison.

Outside of some minor differences of course like, they are practically identical:

  • INTSEL, since it only triggers off 1 ADC
  • SOCxCTL having different channels
  • ADCOFFTRIM/ADCINLTRIM is slightly different, I think that’s to be expected.

 

I’ve also tried this on 3 049 LaunchPads with the same behavior. Wondering if you’re able to replicate on your side?

  • 0
    TI__Guru 60865 points

    Hi Wallace,

    It looks like the F280049C launchpad uses the 100-Pin QFP package of this device, which has VREFHIB and VREFHIC double bonded onto the same pin.  Because of this, the reference of ADC-B will also have to be powered up to use ADC-C (even if you don't want to use ADC-B).  You can confirm this by looking a the contents of the AnalogSubsysRegs.ANAREFPP register: ANAREFCDIS should be set on this package, indicating that ADC-C internal reference is disabled.  

    In general, it is recommended that you power up and configure all ADCs on the device in the same reference operating mode.