Delta Sigma ADC polarity confusion

Question

We have a working circuit that measures motor phase currents and passes it along to an MCU's internal ADC. This is the circuit: Notice that the output will be 'inverted' , so in software we invert it back to get back the correct value.

We want to replace the above circuit with a Sigma-Delta Modulator such as the AMC1303M0510. Reading through the data sheet , they say that if the differential input is 50mv , that would mean a duty cycle pulses of 89.06 %., The MCU's SDFM module reads these pulses and gives out a value based on the resolution set in software.(As shown in the figure above)

• The 'Differential input' here is referred as (AINN - AINP) OR (AINP - AINN)?
• If voltage at AINN > AINP, does this mean the Duty cycle is between (50 to 89.06)

OR

• If voltage at AINP > AINN, does this mean the Duty cycle is between (50 to 89.06)

Please help clear this confusion. Thankyou!

Answer 1

well i also work on a 400V motor driver but I use AMC1300 IC .you want see some details in data sheet .

here the long story short . Vin=Ainp-Ainn

INP=0V (Exactly) OP=will give a pulse of 50% duty cycle respect to your frequency.

INP=+50mv(Full scale) OP=1 pulse with 89.06% duty cycle (MCU read as "1" )

INP=-50mv(Full Scale) OP=1 pulse with 10.94% duty cycle (MCU read as "0" )

Clipping mode :

Only Zeros(pulse width 10.96%) are transmitted if input is ≤ –64 mV.

Only Ones (Pulse width 89.06%)are transmitted if input is ≥ +64 mV.

so the consolidated answer is

consider 0V as a center point

If AINP>AINN: Duty cycle is 50% to 89.06% (positive input).

If AINN>AINP: Duty cycle is 50% to 10.94% (negative input).

your assumption is correct.

This is the simulation I've done: Actually it has to be done more precisely and the ADC output is read in MCU only.