TMS320F280039C: Questions on Zero crossing detection logic in ADC PPB

Hello Johnny,

Johnny Chen said:

(1). They want to confirm the internal architecture of Zero crossing detection logic in ADC PPB. Is it detecting with internal comparator, what's the architecture for the logic ?  

Yes, the comparison and detection logic is internal to the ADC module.

Johnny Chen said:

(2). From the TRM Note, it specifies "The zero-crossing detect circuit considers a result of zero to be positive."  What does that mean ? Then, what is the result of non~zero be ? From the bit SIGN in ADCPPBxRESULT Register, not really know about the detection result corresponding to real analog signal. Would the expert kindly explain on this please ?

(3). Does this submodule really use to detect the AC line crossing at zero crossing ? 

Zero-crossing is intended to work hand-in-hand with the offset reference feature (see the PPB block diagram in the TRM). For example, if your input signal had a range of +/- 20V, you would level shift that to 0-3.3V range for the ADC, and then configure ADCPPBxOFFREF = 2048. Now your ADCPPBxRESULT has a range of -2048 to 2047. The PPB result is what is fed into the comparator, and it generates an event whenever a change in sign is detected, from negative to positive or from positive to negative. This event can be used to generate an interrupt, or fed to the EPWM or crossbar.

This is how the zero-crossing logic can be used to detect AC line zero crossing in hardware.

Best regards,
Ibukun