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I have a very small question to ask. Is it ok if a high side current sensor such as the MAX9929 be used as a low-side current sensor as well? Or should I look for some parameter in the datasheet. The reason why I ask this is because this MAX9929 is bi-directional, therefore current can pass in both directions, so that is not an issue. What I am finding confusing is if it is ok to use it as a low side sensor, since how will the IC know if one of its input is pulled to ground ? Won't it only note the voltage across the sense resistor.

(I ask this question since in my circuit, there is some switching which will make the current sensor go from the high side to low side, also I have tested the IC with one of the input pulled to ground, and it worked, but I want to know if it is the right thing to do from a theoretical perspective)

Thanks for the help

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  • \$\begingroup\$ Even though it appears that it will work, I notice that one or two of the performance parameters listed in the datasheet are worse when RS+ is low or below zero. See the common-mode rejection ratio (CMRR) for example. Is there any reason why you wouldn't just choose a part that specifically says it can be used on the low-side? \$\endgroup\$
    – user57037
    Commented Dec 21, 2020 at 10:58
  • \$\begingroup\$ @mkeith , I need the current sensor to be a high side and low side current sensor all in one basically, since my switching circuit will manipulate the position of the current sensor. \$\endgroup\$ Commented Dec 21, 2020 at 11:01
  • \$\begingroup\$ They have those too. Recently I was looking at current sense amplifiers on the TI website. They have some that can be used high-side or low-side. I am not trying to steer you to TI. Maxim probably has them also. \$\endgroup\$
    – user57037
    Commented Dec 21, 2020 at 11:03
  • \$\begingroup\$ @mkeith , thanks for the tip, did not know they existed tbh. I will make some more research and add my findings at the end of the question. Thanks \$\endgroup\$ Commented Dec 21, 2020 at 11:05

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Look at this image on page 9 of the data sheet: -

enter image description here

The sensing resistor can be attached on a rail that does not go below -0.1 volts relative to circuit ground so, if the lowest voltage is chosen to be 0 volts, then that would appear to meet your requirements.

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  • \$\begingroup\$ Ok, I think I agree. since Vin would be 0V and the Load/Charger will be (lets say) 4V, hence it would not that a current in the opposing direction is coming, due to the the potential at each pin right ? \$\endgroup\$ Commented Dec 21, 2020 at 10:59
  • \$\begingroup\$ I come to the same conclusion. However, I do notice that one or two parameters (CMRR and VOS) appear to have poorer specifications at low common mode voltages. \$\endgroup\$
    – user57037
    Commented Dec 21, 2020 at 11:00
  • \$\begingroup\$ @mkeith , yes I agree with your findingd \$\endgroup\$ Commented Dec 21, 2020 at 11:03

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