I am trying to sense current at high side through a load using MAX4172 IC. I have set Rsense and Rout in such a manner to get 1 uA -> 0.1 V. I am also controlling transistor (common emitter config) to indicate 0 V and 2.5 V under certain current values. Under no load condition i am getting getting 0.4 V which increases slowly and reaches upto 0.7 V then fluctuates.

What could be the possible reasons for voltage fluctuations? Thanks

  • 5
    \$\begingroup\$ Please post a schematic, and a picture of these voltage 'fluctuations'. We can't debug your problem without all relevant information. \$\endgroup\$ – Voltage Spike Jan 25 '18 at 20:04

Just read the data sheet and note the following: -

enter image description here

The input bias currents are anything up 50 times higher than what you are trying to resolve and that's just typical values.

This chip will not do what you want by any stretch of the imagination.

If you look at table 1 in the data sheet they recommend that the lowest FSD is 100 mA - you are expecting to resolve 1 uA - that's not going to happen.

  • \$\begingroup\$ same thing is happening to me if i tend to draw current in mAmps. \$\endgroup\$ – Z. Miller Jan 26 '18 at 13:13
  • \$\begingroup\$ @Z.Miller numbers are important here. Please state numbers i.e. expected versus actual. \$\endgroup\$ – Andy aka Jan 26 '18 at 13:21

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