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Since the loads are parallel, they should operate at the same voltage. The PWR board only needs to measure the output voltage of the supplemental battery and the DC-DC converters
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Current Sensing
Accuracy
The main benefit purpose of high-side current sensing is the ability to detect a short circuit in the load or the harness. There are few solutions to current sensing:
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the current sensing is understanding how much power is being used by each system while the car is driving/racing. The data will be used to identify systems with high power usage for future optimization. It is more meaningful to track the power consumption of each system relative to the total power rather than the absolute value.
The target power consumption of MSXIV's LV system is 20 W. A reasonable accuracy will be the +/- 0.1% of the total power. Given the supply voltage will be 12-13.5 V, the current sensing circuit should be more accurate than +/- 1.5 mA.
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Locations
Given the HSD will be responsible for disconnecting the load when it is shorted to ground, there is no safety advantage for high side current sensing. There are three locations for the current sense resistor:
- Low-Side
- Easier to implement
- Requires a 100 mOhms current sense resistor which consumes some power
- High-Side
- High immunity to ground disturbance
- The common-mode voltage tolerance of the differential op-amp must be greater than 12V
- HSD Current Mirror
- A HSD built-in current mirror with high gain plus a current sense resistor should use less power than the low-side sensing (needs proof)
- The accuracy is around +/- 30% for low current (< 100 mA)