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Sensing hardware prototype developed and tested - Version 1
The voltage reference circuit (Figure 1) provides a stable voltage of 12 V, and -12 V using an external buck-boost converter. The current sense amplifier needs these voltages to provide a linear output voltage in the 0 to 3.3 V range. Note that -12 V is not needed, but some negative voltage is needed for the current sense amplifier to operate in a linear area when there is no current through the shunt.
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The shunt value is chosen so that it does not dissipate too much power with a maximum current of 5 A passing through it. Shunt voltage drop must not be too high for the load to work (High side current sense). The selected shunt is presented in Figure 2.
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Differential low pas first order (Figure 3) filter is set to 150 kHz cutoff frequency. This value is chosen according to the specification of the current sense amplifier.
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The high-side current amplifier amplifies voltage drop on the shunt, representing the linear scaling of current passing through the shunt. Gain is set that for current of 5 A through a shunt of 75 mΩ generates 3.3 V on the input pin of ADC.
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The sensing circuit is implemented as Arduino compatible shield as presented in Figure 5
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The complete sensing circuit spice schematic is available on the official GitHub repo.