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LMP8603: Bidirectional Current Sensing using Offset

Part Number: LMP8603
Other Parts Discussed in Thread: TINA-TI


We have designed in the LMP8603 and are currently in developmental test of engineering model units of our PCBs. The LMP8603 circuitry does not seem to be working according to the spec. Below is the photo of how we are using it, which appears to be according to the datasheet. However, current is only being sensed unidirectional. 

I expect that when no current is applied, the output should read ~2.5V due to the offset. 

Here is what is actually happening. A1/A2 is reading roughly 2.25V, and the output is reading 0.2V when no current is present. 

  • Hello Elizabeth,

    I believe the problem lies with your input circuit, as the connections to all the other pins of LMP8603 look fine. 

    On your input network as drawn, it doesn't look like there's any place for current to flow other than into the pins of the LMP8603. Is this how your PCB is wired? There should be a path to GND or some other return current node rather than wiring back around to the -12V bus voltage. I suggest probing the voltage at the input pins of the LMP8603 to see what is actually being applied to the device, both common-mode and differentially.

    Please below for a typical example and a TINA-TI circuit you can use for debug.

    0172.LMP8603 Test Circuit.TSC

    Best regards,

    Ian Williams
    Applications Manager
    Current Sensing

  • Hi, 

    The circuit i have works, but only for unidirectional current sensing.

    When no current is applied and IN- is floating, A1/A2 is reading roughly 2.25V, but the output is reading 0.2V. I expect that when no current is applied, the output should read ~2.5V due to the offset being tied to 5V VCC

  • Hi Elizabeth,

    Can you please provide a complete schematic of the LMP8603 circuit for me to analyze? I need to see what is going on at the input.

    Best regards,

    Ian Williams