Current Sensor Design

currentsensorschematics

This is my current sensor. INA210 comes with a fixed gain of 200. Other variants have different gain. I like this concept because it saves me passive components and space on a critical area + the resistors on the chip have better accuracy. R16 and C5 is the low pass filter. INA210 is bi-directional and high side. The Circuit above is low side design since I Mount IN- to ground.

currensensor

This is the PCB snip. R1 (cyan) is the current shunt. The two place via connectors are the IN+ and IN- measuring the current. I am real happy with this layout because the sensor leads are so short that it will minimize noise introduction. Notice that I am deliberatly placing the place-via on the solder pads on the shunt With virtually no distance to the INA210. The low pass filter is added closer to the MCU/Connector. The layout of this worked out even┬ánicer than I┬áhoped, so I will be curious to test this one to see what I get out on noise vs. signal. I am actually amazed as to how much I get out of a two layer PCB – assuming this Works as expected.

I decided to add 4 current sensors and BEMF sensors because the current sensors will be heated as well and if they fail or give errors (drift) while heated they might cause a more serious error. I basically need to test them as I burn the circuit + it’s cool to have them mounted.

The values I plan is 0.001Ohm shunt and INA210 that gives 200x gain. This giver 0,015V at 15A and 3V out to the ADC while the shunt use 0,225W. I am a bit concerned that the shunt is to small, so might need to increase the shunt and reduce gain to get a better signal – we will see. The drawback of increasing the shunt is that a shunt with 0,002 Ohm uses 0,45W, a shunt with 0,005Ohm 1,1W etc. The effect usage on the shunt need to be keept as low as possible.

sc70

I have only been using SMD components for ca 1 year. I started with 1206, continued with 0806 and now I only use 0603. INA210 is SC70-6 body (X4 above) – the two resistors R2 and R3 are 0603 size to give an impression of how small this actually is. I am however not even worried about these anymore – a bit of training and patience does that to you.

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