INA194 – 80V Current Sensor

INA210 that I used earlier is only rated for 26V, and it is a 6-pin extremely small package that was a Challenge to get soldered. I have 9 more chips to destroy before I let INA210 rest, but I will not continue with this for 3 reasons (1) size of a 6 pin package and marking made it difficult, (2) 26V is to limit and (3) I finally discovered INA193 to 198 that is SOT-23 based (larger) and support 80V.

Texas Instruments have a large range of current sensors and the series 193 to 198 is sensors With fixed gain of 20, 50 and 100. The difference between packages are pin layout, but they are all SO-23/5. This is small, but my main struggle With INA210 was to identify pin 1. SO-23 is a little larger and that makes a difference.

Input Voltage on these are 2.7V to 18V, but sensor input support -16 to 80V. No external Components are required, but some fltering is recommended. Prices are in the region of 1.7.- USD for samples – 0.8 USD for 500 volumes. So what gain do I want?

50A * 0.001R = 0,05V and I need a 3Vich so gain 60 – or 50 which is INA194 should be workable. Using a 12 bit ADC over 3V I get a sensitivity of 3/4096, meaning the value 1 represent 0.0007V. Using a 0.001R shunt that is 0.7A direct sensitivity – amplified with 50X we should have 0,014mA sensitivity giving a range 14mA to 50A – in theory.

The alternative is that I double the Shunt and use 20X gain – that will give a 17mA sensitivity, but should be more reliable as we get a better signal/noise situation. The challenge is the effect over the shunt. 50A is 2.5W on a 0.001R and 5W on a 0.002R. I hope to get away with 2.5W since it should be divided by 3, but I need bigger shunts for 5W. This is however a workable improvement for a 15A design where 15A should be 0,45W over a 0,002Ohm.

This is the 3rd reason I want the 3rd sensor on the 50A design – to be able to test current sensors and what I can achieve. Using 50A I need to worry about effect usage, using <50mA I need to worry about signal/noise – so whatever I will be a trade-off. DRV8303 help in the sense that it has a PGA (Programmable Gain Amplifier). You can also get stand-alone versions for that, but they require I2C or SPI. And adding more Gain will not improve Signal/Noise factor or change the size of the shunt.

INA193-195 are a bit expensive, but they are worth it if they do the job. I ordered 10x from Arrow for 18.- USD – they will be here in ca 5 days.

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